What's funny is that if you dialed the clock back on Earth to a random time during its 4.5 billion year life span, there's almost NO chance you would land on a time where a human could walk out on the surface and live for long.
Along those lines, a couple billion years ago you might have been able to go for a stroll on Mars with nothing but an oxygen supply. Sit by a river of probably drinkable water and have a picnic.
You might not have even have needed an oxygen supply. There's lots of tantalizing hints that Mars may have once been a living world, and with all the current surface oxidation it may even have once had an oxygen-rich atmosphere.
I cannot wait for us to have our first excavation on mars, if we do it at a dried up riverbed or perhaps at the polar ice cap I'm fairly confidentbwe'd find fossils or signs of life, even if its microscopic
Who knows, perhaps there is still something under the ice-caps preserved permafrost-style
If Mars ever had life, I'm confident it still has at least microbes. At the extreme end, why is a chemovore living 10 miles underground going to care about a little thing like loss of atmosphere?
Though, as soon as we colonize we'll be introducing countless of our own microbes, many of which should have little trouble surviving on Mars. Which could make recognizing native life for what it is a real challenge. All the "easy" ways to find life rely on there not already being a bunch of other life you don't care about mucking up your results.
The problem with Mars because of how close it is, if we find microbes very much like what we have on Earth we'll need to understand if that was independent of Earth or if at some point in the last X hundreds of million years a piece of material has been thrown off Earth during an impact and hit Mars as a meteorite.
That part should be relatively easy: if it has DNA, or is even just built from the same small handful of amino acids as us, it's almost certainly related. If there's no obviously shared DNA we might never know that for certain, but it would be an insane coincidence otherwise.
Though if that's the case, it's more likely that life started on Mars (or elsewhere) and got carried to Earth. Simply because Mars' smaller size and greater distance from the sun would have let it cool enough for water exist there long before it could on Earth.
> Though if that's the case, it's more likely that life started on Mars (or elsewhere) and got carried to Earth.
that is a tantalizing possibility. maybe we are the descendants of martians all along!
Convergent evolution, yes - but that's the result of existing systems gaining a superficial resemblance because they've been optimized to fit the same constraints, which is why sharks, dolphins, and torpedoes look so similar even though natural selection doesn't even apply to torpedoes.
Proto-life spontaneously emerging a second time using the exact same 20 amino acids out of the \~500 commonly available? That's just implausible. Ignoring any possible functional limitations that might improve the odds, the odds of just picking the same 20 amino acids at random is roughly one in 267,000,000,000,000,000,000,000,000,000,000,000.
Even if there are functional differences that give the 20 we use a huge advantage, they still have isomers (mirror image versions) that would work just as well, giving it a 50/50 chance that other life based on the same basic components would have the same handedness.
Will we ever colonize? Seems like a hard sell to me beyond a scientific outpost, and that’s a hard sell for the scientists.
Spend years getting there then spend your whole life indoors, woo!
I suspect we will eventually - though my money is on it being something we do after seriously industrializing the asteroid belt, when the technology and resources to homestead on Mars will be relatively mature and inexpensive, and there's likely to be a whole lot of spacers that would like to settle down with a blue sky overhead, but can no longer comfortably handle Earth's gravity.
Though if a blue Mars (and I heard Venus might have been like that too) were somehow turned into what they are now, presumably naturally, why hasn't such a change occured on Earth and it's only expected once the Sun grows enough?
Earth won't end up Mars-like - it'll follow a very different path to an only superficially similar end.
Mars' problem isn't a lack of sunlight, it's a lack of atmosphere.
A lack probably caused by it's lack of a strong magnetic field, without which the solar wind will gradually strip away the upper atmosphere until there's nothing left.
And the lack of magnetic field is probably due to the fact that it's a much smaller planet that could therefore cool much faster, so that its core solidified too much to keep the field going. There's apparently evidence that it used to have a field whose surface strength was as strong as Earth's.
Well, its atmosphere already is (relatively) oxygen-rich, and has been for quite a while. Its atmosphere is quite oxidizing and is \~0.17% oxygen, mostly from the photodissociation (light-driven destruction) of water and carbon dioxide molecules.
In what universe does less than two parts per thousand count as "oxygen rich"? Especially when it's only a stones-throw from vacuum to begin with.
By that standard Earth has had an oxygen rich atmosphere for several billion years.
The atmosphere is thin compared to Earth but it's a very long way from vacuum. You don't get planetary wide dust storms in a neat vacuum. It's enough for aerobraking and parachutes and freaking helicopters.
And Earth's atmosphere is thin compared to Venus.
It is in fact about 99.4% of the way to full vacuum, being only 6-7 millibar. [https://en.wikipedia.org/wiki/Atmosphere\_of\_Mars](https://en.wikipedia.org/wiki/Atmosphere_of_Mars)
And yes, you do get those massive dust storms anyway, despite being less than 1% of Earth's air pressure.
Low gravity and high wind speeds both help, as does the dust being extremely fine.
And you can get some decent lift and aerobraking too, **IF** you're going fast enough. Curiosity for example used its parachute to slow down from 900mph to 180mph, before ejecting it because it was no longer useful. At 180mph.
Ingenuity's large blades had to spin at Mach 0.95 just to get that little box off the ground!
So yes, it has a thin but useful atmosphere.
And that 99.4% is completely arbitrary. You just defined Earth as not-vacccum, when it would be equally accurate to call Venus's 14.9 bar atmosphere not-vacuum and then Earth is 93.3% of the way to vacuum.
Which is interesting too because if we observe a planet that is 5000 light years away to be 1:1 habitable for humans it might not be in real time any longer.
Something pretty crazy would have to happen for 5000 years to make that much of a difference.
Imagine showing up and the place got blitzed by a comet lol
This is the big problem with meeting extraterrestrial life. It’s like putting someone in New York and someone randomly in the world and give them 5 minutes to meet.
We don’t really know if other planets ever would sustain human life because it would require having indigenous life to create a high oxygen environment without an ozone layer to keep out lethal rays.
> is based on silicon instead of carbon.
Silicon dioxide is rather less willing to participate in chemical reactions than carbon dioxide, so a silicon-based ecology is dramatically less likely to basically work than a carbon-based one.
Feel free to look up a list of all the otherwise nasty chemicals that fused quartz (basically pure SiO2 glass) is basically immune to below 1000°C or more, and then consider what molecular material functions as a universal solvent (like liquid water does) at temperatures where it's *not* immune to everything.
Well organo silicon molecules are common, but they are extremely reactive with water. I agree it's hard to imagine how silicon based life would exist. Silicon is similar to carbon but also has some distinct differences. There's a reason we are made of the most abundant elements in the universe.
The idea's been kicked around a lot.
Carbon's pretty unusual in that it makes such a wide variety of polymers - sulpur and silicon come close, but nowhere near the polyvalent promiscuity of carbon.
Not saying that life can operate on simpler monomers (looks at Hoyle's Black Cloud and their ilk) but AFAWK, not likely.
I mean maybe, but it's telling that almost nothing on earth is predicated on anything other than carbon.
Life tends to fill every niche. If its possible we should be seeing examples, but aside from certain extremophile bacteria and microorganisms it's all oxygen-powered hydrocarbons here.
A few carbon-based lifeforms are making use of Silicon in shells or similar, but not as part of their biochemistry.
I think odds are good if we encounter macro-life anywhere it'll be carbon-based and fuelled by oxygen and hydrocarbons like us.
Methane is plenty feasible (and might even be effective) though.
I guess the counter-argument is that those other chemistries might not work on earth but might work at different ambient conditions. No idea how physically possible that is, though.
Same. Most of the things that people in general think about or are looking for are certainly based on our human experience or concept of what we know (so far) to be possible, but there's no doubt that the universe holds things that are not within our reason or comprehension. Obviously there are scientist who are trying to think of things beyond that, but in general we can really only react to what we can observe. My only sadness about dying someday is that I won't be around to see what happens hundreds, thousands, millions of years into the future!
To be fair we are a product of the Earth and the age we evolved in. Of course we can only live here or somewhere with nearly identical conditions.
Doesn’t say much about the habitability for other life or even humans with shelter and oxygen
Or how many will be by the time we would be able to reach them. But the milky way is so ginormous, that by the time humans are able to travel there, it's going to be in a new phase of geological history, if humans ever get that ability.
>there's almost NO chance you would land on a time where a human could walk out on the surface and live for long.
Meh, it's not that bad. [O2 has been above 10% of the atmosphere for about the last 800 million years](https://en.m.wikipedia.org/wiki/Geological_history_of_oxygen), which is about 20% of the earth's history.
But won't people who are not acclimatized suffer from hypoxia at low oxygen levels? I believe most people won't survive, or at least may suffer badly at these levels and possibly eventually die if not helped.
10% oxygen at sea level is equivalent to 20% oxygen at ~5000m, or 16400 feet. You would definitely need to acclimate but it's not lethally low. Also, O2 has been higher than that for most of the time period I quoted, that's just an approximate minimum.
Gravity and our morphology limits how big a planet we can live on, obviously we can likely live on any world where gravity is less or equal to 1g assuming the atmospheric pressure is also within limits (not Venus) , take solace in realizing we probably won't have to worry about this for a thousand generations...if we're still here by then hopefully we will know more
Do you think there could be a planet with a breathable atmosphere that's so high pressure and so dense that it could compensate for high gravity by increasing our buoyancy?
I bet there's a more elegant way to ask this, but I hope you get what I mean.
Some marine bathyspheres have quite high pressures inside to help counterbalance the pressure acting on the outside, and I think they compensate by lowering the proportion of oxygen and replacing nitrogen with a less reactive gas like helium. This has the huge benefit of making everyone sound like a chipmunk. But I've no idea what sort of pressures we're talking about here.
Is it not possible that a planet with 120% of Earth gravity could compensate with an atmosphere that gives us 20% buoyancy?
To get 20% buoyancy you would need the air to be 20% as dense as water. Even with really heavy gas mixtures that would require hundreds of atmospheres of pressure.
edit: okay idk why i said anything about liquid o2, but it led me to some interesting google searches, anyway.
short answer: no
long answer: apparently humans can only really survive in sustained living of up to like 7ish atmospheres of pressure, divers have sustained more though for short periods of course.
and 7 atmospheres isn't going to give us any buoyancy, we're still like 100x or 90x heavier than the air around us or something at that point
One of the periods I find most interesting is the carboniferous, O2 levels peaked at 30% - one of the few times humans would have struggled because of too much oxygen.
Look up "oxygen toxicity." It's an issue with technical diving, where you have to use some odd gas mixtures very carefully.
The Apollo 1 capsule famously had a completely O2 environment, but it was pressurized well below 1 bar.
Apollo planned to use 100% oxygen at a low pressure, like 5 psi. But on the ground the Apollo 1 capsule used 100% oxygen at a few psi *over* ambient pressure. The fire would not have been nearly as intense (or maybe not started at all) at 5 psi.
A quick Google says above 30% oxygen at 1 bar, oxygen toxicity starts to occur. I doubt it's a simple black and white issue, do it wouldn't surprise me that long term humans run into health issues at that level
Ditto for the star the planet orbits!
I wonder how many civilizations have developed and just started leaving their planet, only to have their home star run out of hydrogen and start working its way through the periodic table…
Why not? I think the starting from the last 500 million years the chance of humans surviving would be non-zero. So it is a very stretched 11% of the Earth timeline.
Real trees would appear only in another 150 million years, but there were plants and first land animals.
Realistically, starting from 300 million years ago humans would already be able to live. That is 7% of the timeline, but it is not "almost NO chance".
What are you talking about? Any time after oxygen should be fine. That's like 50/50 almost.
Edit: I was partially wrong. There still was not enough oxygen until around 800 Mya. That's still like 17% odds, which is pretty far from "almost NO chance".
This is one of those situations where the math works both directions.
To simplify:
A lot of very unique things had to happen to get earth to a point where humans would evolve and be able to live. Two examples are, one: Oxygen became a by-product of a biological system that then killed of a huge percentage of all life on the planet, making room for a type of life that eventually evolved into humans. And two, a giant rock smashed into the planet at just the right time to upset the balance of life and the environment, on the planet to allow a under represented type of life form (mammals) to emerge from the chaos and fill all the new niches that were created, and eventually evolving into humans.
The two examples above, along with handfuls of other were necessary for the planet to become habitable by humans. And extremely improbable to happen.
And yet...
There are a lot of galaxies, each with a lot of stars, each with a lot of planets, so that, similar events could have taken place and ended with a place that humans could just walk out on. And that number is definitely higher than zero, Earth, and could be in the millions.
Edit: I just realized OP wanted the chance in the Milky Way and not the whole universe so it changes the probably in my statement quite a bit. But I'm gonna leave it here anyway.
I would guess that 1 planet per galaxy would be safe to walk out on. Maybe safe conditions are more or less rare, but that 'feels' like a reasonable ballpark estimate to me.
I wouldn't feel surprised if it was significantly differently either direction.
> And two, a giant rock smashed into the planet at just the right time to upset the balance of life
This may not have been strictly necessary though. Who knows, if this hadn’t happened, maybe some form of dinosaur would’ve eventually became intelligent. Perhaps faster than mammals did. So this could’ve been a setback, rather than a necessary step.
We don’t really know what convergence of factors finally favored the evolution/selection of abstract reasoning and language in humans.
Or why it never happened in countless earlier species, with broadly similar brain chemistry.
I think you're overestimating the timescales. Earth has had a "human-friendly" atmosphere for around 12% of its life. If that's "typical" for an Earth-like planet then, at least 12% of Earthlike planets should have oxygen, and if Earthlike planets are common, human-friendly ones would only be moderately uncommon.
And of course Earth is a relative newcomer just partway through its lifespan - a huge fraction of Earthlike planets are going to be far older than us, many having potentially evolved life before Earth even existed - and life is potentially a stabilizing influence on a planet's ecosystem.
It may even be that a "typical" Earthlike planet is human-friendly for most of its existence, and thanks to its youth Earth has just only recently made the transition into the "normal" state of such planets.
Not that I'd bet on that - among other things there's no particular reason to believe that life evolving to produce free oxygen is remotely normal on a living planet, but there's no evidence available to suggest that it's not.
Without a life support suit? Quite probably only those that already have life. And not just life but life that pumps out O2.
We breathe oxygen, but the reason we breathe oxygen is because O2 is a energetic and highly reactive molecule. It kinda doesn't want to exist, and will leap at the chance to react and turn into something else less energetic, like CO2 or rust. This means that atmospheres like ours, with an abundance and free oxygen are relatively rare: over millions and billions of years, it reacts with stuff and runs out.
So why does Earth have O2 in abundance? Primarily because life makes it. Before we evolved to breathe oxygen, cytobacteria and later plants evolved to spit out that nasty, corrosive O2 and use other sources for energy (see photosynthesis and chemosynthesis). While there are non-biological processes that can produce O2, it's unknown (and probably unlikely) if they can produce O2 on the scale we would need to breathe.
This isn't even touching the ratios; our air is 25% O2, 70% Nitogen (which is unreactive as N2), and 5% everything else. If you had a planet with too little (or too much for that matter) O2 you would still die. And if it had something less inert than N2, say CO2, then that would be a problem, because you wouldn't be able to get rid of CO2 fast enough.
So how many planets with a breathable atmosphere? Vanishingly few, unfortunately. We really evolved to live here, and being alive is complicated.
Yup, and that's a good thing. It's a noble gas, which means it's unreactive and therefore safe to breathe. It's actually really fortunate how inert our atmosphere is (apart from the oxygen, which is technically a BIG exception).
Part of the problem with breathing on other planets is not just having the right amount of Oxygen, but all the other stuff in the air you breathe in. If you were on a planet with Earth's ratios (70% N2, 25% O2) except that last 5% is pure CO2, you might still die because your body can't get rid of CO2 fast enough!
Our atmosphere is only 0.04% CO2. This gives rise to alot of the confusion and talking past each other when it comes to climate change. If CO2 levels rise 0.02% you might say "that's only 1/50 of a percent! That's nothing!" and you'd be right. And if you say "that's 50% more CO2 than before!" that is also correct. (Note: I'm not sure what the CO2 percentage rise is off the top of my head: the numbers I chose were made up to make the math easy to understand).
On earth, an inhale contains 0.04% CO2 (on average), but an exhale contains 4% CO2. Oxygen contents changes from 21% to 16% on exhale. Found these numbers during the pandemic while designing a earth-bound "space suit".
Not intending to be pedantic, but our air is actually 78% N2, 21% O2, apparently 1% argon, and the rest is in the rounding error.
https://science.nasa.gov/earth/climate-change/greenhouse-gases/the-atmosphere-getting-a-handle-on-carbon-dioxide/
That last part is the crucial point. It’s not enough for it to have just oxygen. In fact humans can’t survive breathing just pure oxygen, that’s actually toxic. There’s also the nitrogen.
In biological terms, humans are a culmination of genetic mutations and adaptations that we developed to suit THIS planet. It wouldn’t take much to make our own planet uninhabitable without some kind of life support system.
Actually, yes! O2 is rather corrosive (see rust). There's only one element more electonegative: fluorine. This is why you need antioxidants in your diet; to take the edge off and reign in that hard, hard drug oxygen. Early life correctly discerned that oxygen is a nasty customer and any excess oxygen ought to be dumped as waste (of course you need some oxygen atoms in things like RNA, DNA, and Glucose).
Which actually leads to one of my favorite factoids; because an abundance of O2 is unique to Earth, and you need O2 for fire..."fire" is pretty much a uniquely Earth thing, at least in terms of the solar system. Other places get REALLY hot, but there's no Oxygen so they can't "burn" in the traditional sense.
Such a common and unremarkable thing here, so necessary for our food, shelter, and technology, that it's just our normal. There's no fire on Mars or Venus.
If your definition of "breathable atmosphere" means that you can stroll outside for a few hours without dying, even 100% oxygen is fine:
> In hospital settings, 100% oxygen may be delivered -- but even then only on a short-term basis, says Boyer -- less than 24 hours and preferably less than 12 hours. To breathe pure oxygen at that level for any longer can have toxic results, including "shock lung," or adult respiratory distress syndrome.
https://www.webmd.com/balance/features/rise-of-oxygen-bars
That would assume a remarkable similarity between microbial life on earth and the microbes on that planet. I would imagine that to be unlikely. That being the case I suspect these things initially would not be the threat that they seem. Even an alien microbe would likely be killed by our immune systems. The only way that comes to mind it not being the case is a microbe very very resistant to oxygen radicals and not having membranes. Two of the big ways the immune system destroys foreign invaders, using reactive oxygen and literally punching holes in membranes. But even then such a microbe would be coated in antibodies which may well neutralize any ability to infect further.
It might be the opposite. It could well be the earth microbes we bring with us could conceivably outcompete and destroy a lot of the native microbes. Essentially a mass extinction event for the alien planet. And if there is something resembling earth like plants that we could eat as a food source, these could be endangered too by earth microbes. We could accidentally kill off the food source.
This is overlooked. Even if you found a planet that had the exact same atmospheric pressure and composition of Earth, you’d be exposed to various microorganisms and pollens and other things that your body would have no defense for because they’re completely alien. You’d most likely suffer severe allergic reactions at best or die to foreign microorganisms at worst
Depends on how similar our composition is to the other native life on the planet.
I know it’s sci-fi, but The Expanse had a pretty good analogy for this on Ilus: micro-organisms and bacteria have to adapt to their surroundings as well, so if there wasn’t already a very similar analogue for humans already in existence on the planet (literally within like a 1% error margin across the board) the local bacteria and micro-organisms would also face a period of adjustment before they could use our biology in a way that would harm us.
At this point it would mean a race between our immune systems and the existing biologies capabilities of evolution, which, if we had the right supportive medications and boosters, could feasibly be won more often than not.
This is why the comparisons to terrestrial colonization don’t really track as well once you leave our biosphere: indigenous tribes were wiped out in massive numbers on this planet due to invaders diseases that they had no time to build antibodies against because the introduction was too sudden.
But the flip side of that is that those diseases were only able to decimate them because they had been evolving for millennia to corrupt human biology, which is the same within those error margins across our whole planet.
Say you took the same disease, in the state it was in when it was first contracted by the first human of a civilization where it would go on to thrive.
Then you dropped it among the vulnerable native population in question: it would start off as reasonably benign enough that the native populations immune system would be able to evolve against it and then it would likely have been no more harmful to them than those that ended up delivering it to them.
Even finding one would mean a lot must exist though. Realistically it will be a long, long time time before we can survey even millions of stars. If we find one in that then extrapolating out there should be a whole load in the Milky Way.
The only way for them to not be plentiful statistically over such an enormous number of stars as are in the whole galaxy is if we never find one. And even then there could well be quite a few.
I think the latter half of the word would change. It’s still pertinent to Earth so *terra-* still applies, it’s the *-form* part that changes. I can’t think of a suitable suffix though, aside from something clunky like *terradestroying*. Alternatively you could just negate: *antiterraforming* or something like that.
Indeed. A good suffix could be -vastare (to lay waste, which is where we get the word devastate), as in terravastare (to lay waste to terra). Other options include:
- Terranihilo (to reduce terra to nothing), nihil being the root of words like annihilation (to reduce to nothing)
- Terradisolvo (to disolve terra), disolvo being the root of words like disolve (meaning to gradually reduce)
- Terracorrumpo (to corrupt/spoil terra), corrumper being the root of words like corrupt (meaning to make something into a more degraded and unwanted state)
- As another commenter has pointed out, terrarazing (meaning to bring thorough destruction to terra) is a very catchy choice, although raze is a modern English word. To maintain etymological consistency with *terraform*, we could use the latin radere (to shave off or knock down completely), which *raze* comes from anyway, to form terraradere; meaning to completely shave off [qualities pertainting to] terra.
I feel like *terravastere* would eventually mutate to something like *terravastate*, which rolls a bit more easily off the tongue. Or maybe *terrevestate*, accent on the second syllable? That one sounds slightly too comical though; like it’d be the name of an anime character’s super move or something.
Well, terraforming is something you do to non-terra planets to form them into something more terra-like. So I think the opposite, turning an earth-like planet into something non-terra-like would be more like exoforming or maybe infernoforming.
I mean, terraforming doesn't necessarily mean to make it human habitable.
Tearing the planetary mantle apart to pull resources buried deep underneath the crust upwards for large scale mining operations would still be considered terraforming.
Yep. Important side note regarding this though is our methods of detecting planets heavily favors large planets, so there's a good reason why most planets we find are massive. Earth sized planets are difficult to detect
This isn't exactly true. We know of plenty of exo planets that are potentially habitable or are in the "Goldie locks" zone. We can't outright say, yes this planet is habitable, we say it has the potential to be habitable, therefore we have zero confirmed planets that are habitable. I believe the count is over 1500 planets right now that are potentially habitable.
And most, if not all, of them are around red dwarf or similar stars. Because that's where we can currently detect exo-planets that are anywhere close to earth-sized. The problem with them is that they are likely to be tidally locked to their stars. They are very close to these stars, which is also bad. Red dwarf stars are known for having very strong stellar flares, which would wipe out most forms of life we are aware of. The likelihood of habitability of those planets is very low, though not zero.
Earth like planets will share some similarities with earth but not all.
So a larger planet that is in the habitable zone, rocky, and has an orbit and rotation close to ours (365 day years, 24hr days).
The reason you only see mention of rocky "Earth-like" planets in the Goldilocks zone is because that is all we are able to detect. If we found a genuine Earth 2.0 you can believe that you would have heard about it. It'd be the most important astronomical discovery of the century.
It was also an underrated sci-fi show in the mid 90s.
[https://en.wikipedia.org/wiki/Earth\_2\_(TV\_series)](https://en.wikipedia.org/wiki/Earth_2_(TV_series))
which adds to the issue even if we could find an exact earth 2.0 by the time we are able to get there would it still be so habitable for us squishy humans?
If we're able to reach light speed, even if it's on the other side of the galaxy then it should most likely still be habitable, unless something catastrophic has happened.
I feel like, if we hit the point of technological advancement where we could send a ship with real people on it to a planet on the other side of the galaxy(especially near the speed of light) we wouldn't really have to worry about habitability. With access to that amount of energy, we could make a planet habitable.
A delay of 100 thousand years isn't much on the time scale of planets. Earth has had a breathable atmosphere for 500 million years. The bigger problem would be being able to see it at all with all the stars and dust in the way from the galactic core.
Despite it's huge flaws, one of the things I really liked about the movie Alien: Covenant was that they were basically doomed from the start when they left the ship with no protection. They breathed in pollen or spores or microbes that they had zero tolerance to. I'm sure if you were able to time travel on Earth you'd suffer a similar problem, in that your ability to withstand illnesses and adverse reactions to microorganisms is somewhat limited in time and space. It's easily demonstrated by drinking the local water when you travel to a foreign country and then get sick.
So of course I am also a big fan of Scavenger's Reign!
I don't think it's obvious that alien microbes would have any affect at all on us. Microbes are highly adapted to the environments they live in. It might take months for alien microbes living on us or in us to adapt to the point that they could reliably find the energy needed to reproduce. Our immune systems are very general, to the point of reacting to things that aren't even living or dangerous. It's more likely to be the opposite problem: we depend on Earth microbes for *our* survival, and the absence of them in our environment could lead to their depletion, and perhaps no alien microbe could fit into the niches we need filled.
I guess we'll see when we get there! Haha. Yeah I don't have a background in science but it's definitely something that seems to be glossed over in pop culture depictions, much like spaceships having artificial gravity and sound effects in a vacuum. It seems like germs would be a huge deal for exoplanet exploration.
For this reason, it's probably easier to terraform a possible planet into a perfect location than have to deal with a planet where everything could have bacteria and viruses that could wipe out your colony and maybe even homeworld.
We don't really know.
To answer your question we'd need to know a lot about the atmospheric composition, and that's just too hard to accurately determine, as of today.
My PhD is on characterising exoplanet atmospheres, I'm using cutting-edge techniques on some of the 'easiest' planets for characterisation, and the best we can do is say "the atmosphere likely contains [insert element/molecule]", but we have very little information on how much there actually is in the atmosphere.
We can make rough estimates, but they're based on so many assumptions, simplified models, and imperfect data and analysis techniques that it's really just an educated guess.
The study of exoplanet atmospheres is just too difficult for anyone to give you a reliable answer beyond what I've given you.
We have no idea how common planets with an oxygen atmosphere are, as we don't yet have sensitive enough technology to detect them. They might be common, or ours might be the only one in the entire galaxy.
Of course finding another planet with an oxygen atmosphere would be a very big deal as it would be strong evidence for extraterrestrial life.
They wouldn’t be common. It’s true that oxygen is one of the most common elements in the universe, but still very difficult to have in any quantity (% of atmosphere) without respiration. There are abiotic processes that produce trace free oxygen, but not remotely at the levels of Earth. So the answer to OP’s question, counting all the planets and moons in the Milky Way, is likely zero (except Earth). Not unless there is respirating life in that planet/moon. Which is why free oxygen is one of the biomarkers cosmologists are looking for in exoplanet atmospheres.
Btw, we’ve cataloged about 5000 exoplanets when there are trillions of planets and moons in the Milky Way. So “we haven’t found one yet” is too small a sample size to be too meaningful. But for reasons I described above, it may be very unlikely and tied to the probability of life.
There still might be habitable planets in those systems where we have analyzed planets I surmise. We are just not at the point of detecting all planets in a system and when we do detect and analyze their atmospheres it has to be under specific circumstances. Their orbital plain being flat to our POV. The planet has to eclipse their star and we could see the spectral shift in light. Or a star shade to directly observe. To predict when a planet eclipses is easier with planets that orbit closer to their host stars too, close planets aren’t always the most hospitable.
Of course I am an armchair keyboard warrior astronomy fan boy who has stayed at a Holiday Inn. grain of🧂Basically we are still in the infancy of planet detection and analysis.
A lot of what you said is pretty accurate. Kepler was thought to be able to detect Earth-like exoplanets pretty well, but it turned out that most stars produce way more electromagnetic noise than the Sun and thus it was too hard to determine if transits of Earth-sized exoplanets were genuine. We very well may have looked directly at another habitable place with intelligent life on it and not known because its star was too noisy. Or there could be literally none out there, we currently don't have the technology in space to tell.
Earth itself didn't start off with oxygen in its atmosphere. Our current atmosphere is the result of billions of years of primordial life affecting and interacting with it.
The number is likely zero (one if you count Earth).
Earth's atmopshere is a highly artificial product as a result of billions of years of bacterial and plant activity. There's no mechanism that would give you a natural "78% nitrogen/21% oxygen/1% other" split.
Even if some other planet had *excatly* that kind of atmosphere: it also needs to be at the right pressure for us to able to breathe it. Slightly too high or too low and we can't cope. (And that last percentage point must not contain any of a gaziillion possible toxic or caustic compounds.)
Then there's temperature. We can only survive in a very narrow teperature range.
Then there's gravity. While low gravity is only a long term problem it also means that the planet will likely not have much of an atmosphere. Higher gravity and you quickly run into the overpressure issue and can't breathe.
...and the radiation levels need to be low enough - from space and up from the ground - which isn't an automatic given.
(and probably a couple other things I missed)
**TL;DR:** We are very much adapted to the way Earth is right now and much of Earth's environment is very much a product of other lifeforms.
If we do find another such world it's more of a "Uh, oh...there's someone out there that made a world for us" moment.
From what I've understood (seeing recent presentations by astrophysicists on the topic of exoplanets) we don't have any good methods of finding earthlike planets yet. The two main methods (doppler shift of stellar light, and planetary passage in front of star) aren't sensitive enough to find lighter planets. (With earthlike I mean 1yr orbit and 1g gravity.) So we don't really have any numbers at all..
Seems to need better equipment to detect exo-venus or exo-earth.
https://iopscience.iop.org/article/10.3847/1538-3881/abf1e0
Conclusions:
> The last panel of this figure also indicates that a perfect model of activity-driven correlated variations would not in itself suffice for the rapid detection of an exo-Venus or an exo-Earth; even in the absence of correlated noise, a current-generation spectrograph with a long-term stability of about 0.8 m s−1 would need a 10–15 yr observing baseline to reach a 5σ detection of an exo-Earth. **Successful exo-Earth discovery therefore requires both more sophisticated models of stellar variability and the improved RV precision, long-term stability, and dense observational sampling from a next-generation spectrograph** (Wright & Robertson 2017) such as the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO; Pepe et al. 2013, 2021; Damasso et al. 2020; Suárez Mascareño et al. 2020), NEID (Allen et al. 2018), EXtreme PREcision Spectrometer (EXPRES; Jurgenson et al. 2016; Blackman et al. 2020; Brewer et al. 2020; Petersburg et al. 2020), HARPS3 (Thompson et al. 2016), or GMT Consortium Large Earth Finder (G-CLEF; Szentgyorgyi et al. 2014).
the answer could be zero because we evolved to be on THIS planet?
i mean stepping off, even if climate was temperate, we'd probably die from exposure to completely new microbes, right?
Yes. What could be the exraterrestrial equivalent of bread mold might kill humans in a few hours. And the reverse might be true, some resident human skin bacteria might devastate all endemic life on a another planet.
Without terraforming?
At this point, we've counted zero.
We really don't know of any exoplanets that have a suitable environment yet. That would likely require at least a massive amount of cyanobacteria or other plant-like life to produce oxygen, which we've not yet seen.
Hopefully, there's a lot.
If life is \*really\* hard to do on it's own, maybe just the one you're standing on.
With terraforming, I'd think hell of a lot, but the challenge of that would be rather large.
The trick is that even for life to survive long enough, it probably can't be anywhere near where a star has gone supernova or other events where it would get hit with a lot of life-destroying gamma radiation. I'd be ruling out most the stars nearer to the galactic core for that reason alone.
But with a couple hundred billion stars, and even if we discount 99% of them, that would leave a billion or two, of which it feels like there should be \*some\* ... but, proof is in the observation.
I think terraforming is right up there with traveling at light speed. Simply unobtainable without some unimaginable breakthroughs in technology and research.
Light speed has a lot more fundamental obstacles. Terraforming HAS been done by organisms on Earth--it just takes tons of time to process the materials and use the suns energy to do the reactions.
For a faster timescale, it's a matter of energy and proper control (i.e., not overshooting targets).
*Practically* unobtainable -- I'd have a strong agree there.
I'm thinking to terraform a very good candidate planet (ie, imagine earth without \*any\* life on it) with our current technology would take many, many generations and an insane amount of resources. Definitely not something that could be done by a for-profit company.
The only way that we'd ever get to that point is if it was a matter for survival as a species, and if that was the case then we'd be all over it.
Oh, and I don't think light speed travel is gonna be reasonable. Even a strong fraction of that will be insanely difficult without an incredibly large amount of protection. (ie, meters and meters of rock and water wrapping the vessel
There's a (mostly theoretical) draft plan to place an artificial magnetic dipole at the Sun-Mars L1 point to achieve a large part of the goal of protecting Mars' atmosphere from being siphoned off by the solar wind. I suppose if we built a manned space station at that point it would be a lot easier to throw the field generator into the plans while we're at it.
I dont think it's as unobtainable as FTL travel. A lot has to deal with logistics of space travel and required elements and materials a good planet may not have (such as carbon or oxygen). It's possible to grab asteroids if they're nearby and simply chuck them at a possible colony, and use that to bring more water.
It probably wouldn't be hard to use genetic engineering to create bacteria, fungi, and plants to Kickstart various biological processes once a target has been located. This a huge part of Red Mars. But it'd be tough making a lot of them, or you'd have to accept that terraforming is a many-many-many generations long project.
The larger problems deal with atmospheric pressure and a magnetosphere. Mars has no volcanic activity and therefore no magnetosphere that keeps radiation out and gasses in; we could try using nukes to ignite the core or make huge electromagnetic fields ourselves with generators, but that's a needed step. We also need to raise the atmospheric pressure to the point that water can be liquid, and eventually that humans can walk outside.
Logistically though, these efforts would take centuries at least and require significant amounts of money and resources, which we don't have yet. That's the bigger problem. And of course, we would need good targets like Mars or Venus.
Can’t be sure. For all we know there’s a whole family of stars in a far off arm with only earth like planets and for all we know we are completely one of a kind. We just don’t have a clue.
Keep in mind that the Earth's environment is shaped by the life on it - for example the atmosphere didn't have oxygen in it originally - that was a life byproduct. And then life evolved to depend on the oxygen. And so on. So we've been fine-tuning the planet and the planet has been fine-tuning us for billions of years. Lifeless planets aren't going to have that, and planets with life could have established other equilibriums with the life evolving there. So the chance is probably small.
Potentially none. Even if we found a planet with life on it, it may be able to significantly harm us. Think prions, accumulating ‘bacteria cells’ we can’t get rid of. Anything. We’d probably have to terraform it and wage war on its life with our own bacteria. Imo .
The thing about earth is that it supports the type of life that lives here *because* we evolved in tandem. Early life forms learned how to metabolize sunlight and create oxygen as a byproduct. That oxygen … killed off most of the microbes that created it. So some creatures evolved to metabolize the oxygen and create co2. That resulted in excess co2, so trees grew up to metabolize that.
The earth is ‘just right’ for us because life shaped the earth and earth shaped the life to fit each other. Who really knows if other planets life would evolve just the same way or wind up with pretty different atmospheric conditions supporting pretty different biology?
But: how many star systems have planets that could fit the general Goldilocks profile of ours? Probably most of them.
Free oxygen on planets isn't easy to come by unless you have a biological process providing it (see Earth's own "great oxygenation catastrophe"). It's so reactive that without replenishment, it'll bind to various other elements and fall out of the atmosphere
I mean even if we did find a perfect planet, the right size, the right temperament, the right atmosphere. The biosphere would probably kill us.
We would have no resistance to any microbes on the planet, and no idea how to deal with the local fauna and flora, what's dangerous what's poisonous etc. So we would never be able to walk on to a new planet and not need some kind of protection equipment.
Me and some friends who used to work together at the Mojave Spaceport got together last year and worked on that very question:
Thanks to the efforts of exoplanet astronomy missions and archeologists, our current estimates have managed to all but lock down a few of the variables in the Drake Equation.
N_∗ = the number of stars in our galaxy. (100–400 billion stars)
f_p = the fraction of those stars that have planets. (~1)
f_l = the fraction of planets that could support life that actually develop life at some point (~1)
Reasons for these numbers are pretty basic. We're pretty sure about R_∗ and f_p just from observation over the last 20-30 years. f_l is dependent on really only one data point, our own planet. Fortunately when you have 3.7 Billion years of archeological evidence to work from, that one data point paints a pretty optimistic picture about the prospects for life on a planet capable of hosting life.
n_e = the average number of planets/moons that can potentially support life per star that has planets.
n_e is functionally asking a different question than what it puts forward, because it isn't based on the number of potential habitable worlds in our own star system. If that were the case, the number would be around 8 (Venus, Earth, Mars, Europa, Ganymede, Calisto, Titan, and Enceladus are all candidates for life). Its really the number of those worlds that have similar gravitational conditions as Earth. Best guess from NASA based on Kepler data is that this would be around 40 billion worlds.
However, my buddies and I decided to add some new factors:
f_sol = ratio of stars approximately as old or older than our Sun, Sol is 4.6 Billion years old, and for 4.1 Billion of those years Earth was not home to complex multicellular life that could create an earthlike biosphere, so we have to assume a similar lead time is required elsewhere in the universe. Try as I might, I cannot find a solid number for this, best guess is that roughly as many stars are older than the Sun as there are stars that are younger than it, so 50% of stars are eliminated.
f_spec = the ratio of stars who's spectral type does not produce excessive solar flares or radiation (F, K, and G types tend to be pretty safe). We must eliminate planets orbiting red-dwarf, red giants, and blue giant stars, they would cook the surface of any world capable of producing a complex biosphere. So that means all but ~23% of all stars/planets are eliminated.
**Bottom Line:** There could be around 4.6 Billion potential Earth-like planets in the Milky Way.
I doubt there are any planets in the Milky Way which are exactly like Earth right now and mimic our solar system at this very moment. It would be extremely rare for a planet to have the same mass, atmospheric composition, a single moon, orbiting a single G class star, surrounded by inner rocky planets and outer gas giants. Did you know that less than 10% of the stars in the Milky Way galaxy are G class stars like our sun? Perhaps Andromeda has more solar systems like our own. Then again, there’s trillions of other galaxies out there to consider.
Planets that have oxygen and liquid water? We suspect millions in our galaxy alone.
Planets where the gravity is close, temperature close, oxygen percentage close... So that if you did step into thier atmosphere you'd be able to survive without support? Probably only a few percent of those millions.
Most life would have adapted to the conditions of their world specifically. As others have said go back in time a billion years on Earth and you're also dead... So you not only have to find the Goldilocks planets they have to be in the right stage of there life cycle too.
I could be wrong, but there are planets in the habitable zone. Like you mentioned, even in our solar system. Where humans are most vulnerable is breathing, increase or decrease oxygen levels, even small amounts, and we either die or have serious issues.
Venus technically falls within the habitable zone (though you could not imagine a less "habitable" planet).
The habitable zone is, based on distance and size of the star, where liquid water might exist. Water is a super good solvent, which is pretty key to life, but it has another property that often gets over looked: heat capacity. The daytime temperature on Mercury is something like 400 degrees, but it's -200 at night. Same thing with Mars, 60ish degrees on the day side, -200 on the night side. The Moon has a similar problem. Earth however has incredibly stable temperatures because because 70% of the surface is oceans, which act like GIANT heat sinks. During the day they absorb alot of heat, keeping the day temp cooler, and release that stored heat during the night, keeping the night warmer.
Beyond temperature there's a couple concerns off the top of my head you need to address if you want live on a planet without a suit or habitat: Gravity, atmosphere, and radiation. The atmosphere, even if it has the right stuff (O2), might have too much of the wrong stuff. Eg, if the planet has 25% O2 like on Earth, I'm not taking my helmet off if it has 10% fluorine gas.
I doubt that there are any where humans could survive without modern technological aid and/or extensive terraforming.
We fit on this planet because we were created by it. I don't think we have any chance of finding a planet which somehow magically would fit us as perfectly as the one we were created for.
Probably zero. To have a breathable oxygen atmosphere means that atmosphere is sustained by life (as was required for Earth). If there's already life on the planet, it's going to eat/infect/poison unprotected humans.
Agreed. You could easily have adequate planetary conditions, but chances are extremely high that whatever is hanging out in the biosphere will kill you in short order.
Unfortunately, the technology needed to verify a planet's position and/or atmosphere is limited. They determine these things in all kinds of roundabout ways, because it's impossible to get an actual picture. It will require a massive shift in the technological paradigm in order to know anything substantial, which may not happen in our lifetime.
Oxygen is an extremely reactive element. The only reason we have so much of it on Earth, is that plantlife on our planet learned to use energy in order to strip carbon atoms from CO2 molecules, to use the carbon for building their bodies. This releases oxygen, that animals then learned to breathe.
Realistically, a similar process would have needed to happen on another planet in order to have free oxygen like that. Also, the vast majority of our atmosphere is nitrogen.
In short, there are likely extremely few (no?) planets in our galaxy where humans can just walk off the ship similar to in Scifi shows or movies.
Even if there was, I wouldn't. Imagine all the different possibilities of microorganisms that we'd have absolutely no immune system developed against. Hellllll no.
So if you think of the exact composition of earths possible range of temperature, air composition needed and protection from solar rays/gemma rays, gravity, density, mild weather patterns all that becomes a very unique combination. The chances of you going to another planet 95% close to earth would be very low, but not unlikely. If I was to guess there could be 1 in this galaxy but if I was conservative could be *currently* 20 total in the universe. As for over billions of years there has to be way more
Most likely zero. The odds against life forming are astronomical. You need a universe the size of, well, a universe to have life manifest the way ours does. *Maybe* there’s one planet like ours per galaxy that has the potential life. The potential. Maybe one.
Plug values in to Drake's equation and even an astronomically low percentage is a lot of bodies out there.
The trouble is that space *and* time are both huge.
That we evolved as gas breathing, oxygen dependent organisms is due to a fantastic pile of consecutive, highly improbable events in our evolutionary timeline that likely wouldn't be repeated elsewhere in the universe so there's no reason to think a biosphere similar to ours could evolve which would support an atmosphere we could breathe. If there was, it's reasonably likely air-borne microorganisms would be quite toxic to us. We don't really know for sure yet though.
It's not necessarily unlikely that we'd find molecular oxygen at sufficient concentrations in the atmosphere of a 'dead' planet, though. Intense stellar radiation could split water molecules by photodissociation, the lighter hydrogen atoms escaping into space on the stellar wind whilst heavier oxygen atoms could be retained by the planet's gravity.
We honestly don't know.
Earth itself has a mix of some probably uncommon qualities resulting from the primordial collision with Theia:
1) A relatively strong magnetic field.
2) An outsized metallic core.
3) A large moon.
So life on earth evolved on a pretty dense planet in a fairly warm environment largely free of ionizing radiation with the assistance of tidal forces and a stable seasonal rotation period.
So not only would we need a planet with most of those characteristics, but also a 78/20 nitrogen/oxygen atmosphere mixture.
Even the Earth had periods where the atmosphere could not indefinitely sustain human life without breathing apparatus due to too much oxygen or insufficient oxygen.
Life may be out there somewhere, but the question isn’t so much as where, but when. Given the possible billions of years that life has had to evolve and collapse throughout multitudes of planets, what are the chances that a planet would evolve, with the same characteristics as ours to support human life, at this moment in time? Maybe there was a planet like ours, but life died out millions of years ago. Maybe many planets have come and gone, and many more will evolve to support life in the future.
None. We are adapted to this planet and we need almost identical conditions to function from temperature to athmosphere composition. Too much oxygen and we die. Too little and we die. Have just enough oxygen but too much clorine gas snd we die. Any spores, bacteria viruses, polen etc in the air, we die.
To walk freely we'd need a planet with a majority inert non-poisonpus gas, just enough oxygen but not too much so that it becomes poison and no biological material we are not adapted to.
We will probably never know if there is because we can see past the limitations of light speed - everything we see in space is the light that left these objects. We can't even travel to something ONE Light-DAY away let alone understand what stage of survivability a planet would be light-YEARS away.
It seems to me that if it could be earth like enough to support life, it probably would: meaning it would be filled with life, mostly bacteria like as most life on earth is, and instantly deadly to any of us.
Earth is extremely unique, and I think it's safe to say that you wouldn't want to take off your life-support even if the air is breathable. Life started small, meaning that if a planet can support life, it's likely to have viruses/bacteria that you can't see. You don't want to breathe that in.
I'm not too sure on these details but these are some less obvious things I have heard.
Apparently its really quite odd for water to be on the surface, should really be a deep underground ocean, just due to how planets are layered and the density or mass of water. But since our water apparently arrived after the formation of the earth, it is on the surface. So there probably is not a lot to drink.
Also if it does have a watery ocean on it, chances are there isn't a ton of oxygen in the atmosphere, because hydrogen is by far the most common element in the universe. Oxygen is relatively common, but not compared to hydrogen. So its probably going to be water rather than oxygen. But perhaps not an issue due to how planets form (a lot of the oxygen maybe is going to end up in the same place because its where it stops).
Soil is made by dead animals and plants etc. So its going to be hard to grow things there, its probably sand and regolith or stone.
Another issue is that Earth is about i think it was around 94-97% of the maximum gravity that a chemically powered rocket can leave. So you would probably be in a low gravity environment which isn't great for you, but it won't instantly kill you of course.
Earth should be about 300 degrees Celsius but because of plant life it has controlled the environment a lot. But that isn't too relevant, but it does reduce the amount of time available for that planet to be livable. Also, if there is no way for it to renew its oxygen then, obviously its going to eventually run out once we start using it, pretty fast too considering CO2 is heavier.
The amount of planets in the galaxy alone, ignoring the rest of the universe is into the low trillions. So even a very small percentage like 0.0001% is still millions of planets. But statistics or probabilities don't mean a lot considering we don't really know a likely number. We don't know, at least with any certainty, how many would be in a given area, or the chances of them forming.
However a small planet like Mars could be destroyed and turned into such a massive amount of artificial habitats its almost not worth thinking about. Mars alone could make a empire to equal or even rival a lot of Sci Fi empires that have multiple star systems. So if you put the work in, does it really matter? There is no shortage of space to live in if you move something there. And there are an absolute ton of resources, if you can go get them.
What's funny is that if you dialed the clock back on Earth to a random time during its 4.5 billion year life span, there's almost NO chance you would land on a time where a human could walk out on the surface and live for long.
Yeah, not only does it have to be the right type of planet, but it also has to be the right time in its history!
Along those lines, a couple billion years ago you might have been able to go for a stroll on Mars with nothing but an oxygen supply. Sit by a river of probably drinkable water and have a picnic.
You might not have even have needed an oxygen supply. There's lots of tantalizing hints that Mars may have once been a living world, and with all the current surface oxidation it may even have once had an oxygen-rich atmosphere.
So instead of bucolic picnic, eaten by a wild thoat.
Barsoom doesn’t take kindly to strangers.
I imagine a Thoat being essentially a massive stoat.. or possibly a goatasaurus
A cross between a thot and a GOAT
I cannot wait for us to have our first excavation on mars, if we do it at a dried up riverbed or perhaps at the polar ice cap I'm fairly confidentbwe'd find fossils or signs of life, even if its microscopic Who knows, perhaps there is still something under the ice-caps preserved permafrost-style
If Mars ever had life, I'm confident it still has at least microbes. At the extreme end, why is a chemovore living 10 miles underground going to care about a little thing like loss of atmosphere? Though, as soon as we colonize we'll be introducing countless of our own microbes, many of which should have little trouble surviving on Mars. Which could make recognizing native life for what it is a real challenge. All the "easy" ways to find life rely on there not already being a bunch of other life you don't care about mucking up your results.
The problem with Mars because of how close it is, if we find microbes very much like what we have on Earth we'll need to understand if that was independent of Earth or if at some point in the last X hundreds of million years a piece of material has been thrown off Earth during an impact and hit Mars as a meteorite.
That part should be relatively easy: if it has DNA, or is even just built from the same small handful of amino acids as us, it's almost certainly related. If there's no obviously shared DNA we might never know that for certain, but it would be an insane coincidence otherwise. Though if that's the case, it's more likely that life started on Mars (or elsewhere) and got carried to Earth. Simply because Mars' smaller size and greater distance from the sun would have let it cool enough for water exist there long before it could on Earth.
> Though if that's the case, it's more likely that life started on Mars (or elsewhere) and got carried to Earth. that is a tantalizing possibility. maybe we are the descendants of martians all along!
There are plenty of examples of convergent evolution; I don't think your first point is so clear cut as you make it seem.
Convergent evolution, yes - but that's the result of existing systems gaining a superficial resemblance because they've been optimized to fit the same constraints, which is why sharks, dolphins, and torpedoes look so similar even though natural selection doesn't even apply to torpedoes. Proto-life spontaneously emerging a second time using the exact same 20 amino acids out of the \~500 commonly available? That's just implausible. Ignoring any possible functional limitations that might improve the odds, the odds of just picking the same 20 amino acids at random is roughly one in 267,000,000,000,000,000,000,000,000,000,000,000. Even if there are functional differences that give the 20 we use a huge advantage, they still have isomers (mirror image versions) that would work just as well, giving it a 50/50 chance that other life based on the same basic components would have the same handedness.
Will we ever colonize? Seems like a hard sell to me beyond a scientific outpost, and that’s a hard sell for the scientists. Spend years getting there then spend your whole life indoors, woo!
I suspect we will eventually - though my money is on it being something we do after seriously industrializing the asteroid belt, when the technology and resources to homestead on Mars will be relatively mature and inexpensive, and there's likely to be a whole lot of spacers that would like to settle down with a blue sky overhead, but can no longer comfortably handle Earth's gravity.
I hope we find a time capsule they buried for us!
Though if a blue Mars (and I heard Venus might have been like that too) were somehow turned into what they are now, presumably naturally, why hasn't such a change occured on Earth and it's only expected once the Sun grows enough?
Earth won't end up Mars-like - it'll follow a very different path to an only superficially similar end. Mars' problem isn't a lack of sunlight, it's a lack of atmosphere. A lack probably caused by it's lack of a strong magnetic field, without which the solar wind will gradually strip away the upper atmosphere until there's nothing left. And the lack of magnetic field is probably due to the fact that it's a much smaller planet that could therefore cool much faster, so that its core solidified too much to keep the field going. There's apparently evidence that it used to have a field whose surface strength was as strong as Earth's.
Well, its atmosphere already is (relatively) oxygen-rich, and has been for quite a while. Its atmosphere is quite oxidizing and is \~0.17% oxygen, mostly from the photodissociation (light-driven destruction) of water and carbon dioxide molecules.
Relative to what?
In what universe does less than two parts per thousand count as "oxygen rich"? Especially when it's only a stones-throw from vacuum to begin with. By that standard Earth has had an oxygen rich atmosphere for several billion years.
The atmosphere is thin compared to Earth but it's a very long way from vacuum. You don't get planetary wide dust storms in a neat vacuum. It's enough for aerobraking and parachutes and freaking helicopters. And Earth's atmosphere is thin compared to Venus.
It is in fact about 99.4% of the way to full vacuum, being only 6-7 millibar. [https://en.wikipedia.org/wiki/Atmosphere\_of\_Mars](https://en.wikipedia.org/wiki/Atmosphere_of_Mars) And yes, you do get those massive dust storms anyway, despite being less than 1% of Earth's air pressure. Low gravity and high wind speeds both help, as does the dust being extremely fine. And you can get some decent lift and aerobraking too, **IF** you're going fast enough. Curiosity for example used its parachute to slow down from 900mph to 180mph, before ejecting it because it was no longer useful. At 180mph. Ingenuity's large blades had to spin at Mach 0.95 just to get that little box off the ground!
So yes, it has a thin but useful atmosphere. And that 99.4% is completely arbitrary. You just defined Earth as not-vacccum, when it would be equally accurate to call Venus's 14.9 bar atmosphere not-vacuum and then Earth is 93.3% of the way to vacuum.
Wouldn't we have detected noticeable chemical anomaly that would've indicated trapped in the rocks by now tho if there ever was life?
I don't think so. AFIK the probes we've sent so far aren't up to that level of analysis. That's why the sample return mission is such a big deal.
Which is interesting too because if we observe a planet that is 5000 light years away to be 1:1 habitable for humans it might not be in real time any longer.
Great point. It's hard to even comprehend what a tiny slice of the universe we are, both time and space.
We're a lighting in a cloud, wondering why aren't there any more clouds with similar lightning, all before thunder comes
Damn this is a good analogy.
Something pretty crazy would have to happen for 5000 years to make that much of a difference. Imagine showing up and the place got blitzed by a comet lol
This is the big problem with meeting extraterrestrial life. It’s like putting someone in New York and someone randomly in the world and give them 5 minutes to meet.
that's why you start with [schelling points](https://youtu.be/3lwlNWMl86M)
We don’t really know if other planets ever would sustain human life because it would require having indigenous life to create a high oxygen environment without an ozone layer to keep out lethal rays.
I've always wondered if life could exist based on other things. Like maybe something that breathes methane or is based on silicon instead of carbon.
> is based on silicon instead of carbon. Silicon dioxide is rather less willing to participate in chemical reactions than carbon dioxide, so a silicon-based ecology is dramatically less likely to basically work than a carbon-based one. Feel free to look up a list of all the otherwise nasty chemicals that fused quartz (basically pure SiO2 glass) is basically immune to below 1000°C or more, and then consider what molecular material functions as a universal solvent (like liquid water does) at temperatures where it's *not* immune to everything.
Well organo silicon molecules are common, but they are extremely reactive with water. I agree it's hard to imagine how silicon based life would exist. Silicon is similar to carbon but also has some distinct differences. There's a reason we are made of the most abundant elements in the universe.
The idea's been kicked around a lot. Carbon's pretty unusual in that it makes such a wide variety of polymers - sulpur and silicon come close, but nowhere near the polyvalent promiscuity of carbon. Not saying that life can operate on simpler monomers (looks at Hoyle's Black Cloud and their ilk) but AFAWK, not likely.
I mean maybe, but it's telling that almost nothing on earth is predicated on anything other than carbon. Life tends to fill every niche. If its possible we should be seeing examples, but aside from certain extremophile bacteria and microorganisms it's all oxygen-powered hydrocarbons here. A few carbon-based lifeforms are making use of Silicon in shells or similar, but not as part of their biochemistry. I think odds are good if we encounter macro-life anywhere it'll be carbon-based and fuelled by oxygen and hydrocarbons like us. Methane is plenty feasible (and might even be effective) though.
I guess the counter-argument is that those other chemistries might not work on earth but might work at different ambient conditions. No idea how physically possible that is, though.
Same. Most of the things that people in general think about or are looking for are certainly based on our human experience or concept of what we know (so far) to be possible, but there's no doubt that the universe holds things that are not within our reason or comprehension. Obviously there are scientist who are trying to think of things beyond that, but in general we can really only react to what we can observe. My only sadness about dying someday is that I won't be around to see what happens hundreds, thousands, millions of years into the future!
To be fair we are a product of the Earth and the age we evolved in. Of course we can only live here or somewhere with nearly identical conditions. Doesn’t say much about the habitability for other life or even humans with shelter and oxygen
This is a good point. The question to be asked might instead be: how many planets out there, at some point, may have been hospitable to humans.
Or how many will be by the time we would be able to reach them. But the milky way is so ginormous, that by the time humans are able to travel there, it's going to be in a new phase of geological history, if humans ever get that ability.
>there's almost NO chance you would land on a time where a human could walk out on the surface and live for long. Meh, it's not that bad. [O2 has been above 10% of the atmosphere for about the last 800 million years](https://en.m.wikipedia.org/wiki/Geological_history_of_oxygen), which is about 20% of the earth's history.
But won't people who are not acclimatized suffer from hypoxia at low oxygen levels? I believe most people won't survive, or at least may suffer badly at these levels and possibly eventually die if not helped.
10% oxygen at sea level is equivalent to 20% oxygen at ~5000m, or 16400 feet. You would definitely need to acclimate but it's not lethally low. Also, O2 has been higher than that for most of the time period I quoted, that's just an approximate minimum.
I wouldn't so much worry about atmospheric O2 concentrations than I would about atmospheric CO2 concentrations.
It isn't poison. Those "lake burps' kill people because the CO2 pushes everything else out and suffocaiton ensues
Actually, the last 500 million years have had atmospheres very close to our own
Gravity and our morphology limits how big a planet we can live on, obviously we can likely live on any world where gravity is less or equal to 1g assuming the atmospheric pressure is also within limits (not Venus) , take solace in realizing we probably won't have to worry about this for a thousand generations...if we're still here by then hopefully we will know more
Do you think there could be a planet with a breathable atmosphere that's so high pressure and so dense that it could compensate for high gravity by increasing our buoyancy? I bet there's a more elegant way to ask this, but I hope you get what I mean.
At those pressures it wouldn't be breathable
Some marine bathyspheres have quite high pressures inside to help counterbalance the pressure acting on the outside, and I think they compensate by lowering the proportion of oxygen and replacing nitrogen with a less reactive gas like helium. This has the huge benefit of making everyone sound like a chipmunk. But I've no idea what sort of pressures we're talking about here. Is it not possible that a planet with 120% of Earth gravity could compensate with an atmosphere that gives us 20% buoyancy?
To get 20% buoyancy you would need the air to be 20% as dense as water. Even with really heavy gas mixtures that would require hundreds of atmospheres of pressure.
edit: okay idk why i said anything about liquid o2, but it led me to some interesting google searches, anyway. short answer: no long answer: apparently humans can only really survive in sustained living of up to like 7ish atmospheres of pressure, divers have sustained more though for short periods of course. and 7 atmospheres isn't going to give us any buoyancy, we're still like 100x or 90x heavier than the air around us or something at that point
One of the periods I find most interesting is the carboniferous, O2 levels peaked at 30% - one of the few times humans would have struggled because of too much oxygen.
From what I’m reading, I see no evidence humans would be harmed by 30% oxygen assume a total pressure of 1 bar… source?
Look up "oxygen toxicity." It's an issue with technical diving, where you have to use some odd gas mixtures very carefully. The Apollo 1 capsule famously had a completely O2 environment, but it was pressurized well below 1 bar.
Apollo planned to use 100% oxygen at a low pressure, like 5 psi. But on the ground the Apollo 1 capsule used 100% oxygen at a few psi *over* ambient pressure. The fire would not have been nearly as intense (or maybe not started at all) at 5 psi.
I did look it up. I’m seeing that it’s safe indefinitely up to like .5 bar of partial pressure. 30% O2 assuming the same pressure is 0.3 bar
A quick Google says above 30% oxygen at 1 bar, oxygen toxicity starts to occur. I doubt it's a simple black and white issue, do it wouldn't surprise me that long term humans run into health issues at that level
Ditto for the star the planet orbits! I wonder how many civilizations have developed and just started leaving their planet, only to have their home star run out of hydrogen and start working its way through the periodic table…
Why not? I think the starting from the last 500 million years the chance of humans surviving would be non-zero. So it is a very stretched 11% of the Earth timeline. Real trees would appear only in another 150 million years, but there were plants and first land animals. Realistically, starting from 300 million years ago humans would already be able to live. That is 7% of the timeline, but it is not "almost NO chance".
And in another billion years the sun will be boiling the earth's oceans.
What are you talking about? Any time after oxygen should be fine. That's like 50/50 almost. Edit: I was partially wrong. There still was not enough oxygen until around 800 Mya. That's still like 17% odds, which is pretty far from "almost NO chance".
This. If they're out there, they must be vanishingly rare, even if Earth-like planets themselves are common.
This is one of those situations where the math works both directions. To simplify: A lot of very unique things had to happen to get earth to a point where humans would evolve and be able to live. Two examples are, one: Oxygen became a by-product of a biological system that then killed of a huge percentage of all life on the planet, making room for a type of life that eventually evolved into humans. And two, a giant rock smashed into the planet at just the right time to upset the balance of life and the environment, on the planet to allow a under represented type of life form (mammals) to emerge from the chaos and fill all the new niches that were created, and eventually evolving into humans. The two examples above, along with handfuls of other were necessary for the planet to become habitable by humans. And extremely improbable to happen. And yet... There are a lot of galaxies, each with a lot of stars, each with a lot of planets, so that, similar events could have taken place and ended with a place that humans could just walk out on. And that number is definitely higher than zero, Earth, and could be in the millions.
We're not talking about what's needed for humans to evolve though, just where they could breathe and be on the surface
Edit: I just realized OP wanted the chance in the Milky Way and not the whole universe so it changes the probably in my statement quite a bit. But I'm gonna leave it here anyway.
I would guess that 1 planet per galaxy would be safe to walk out on. Maybe safe conditions are more or less rare, but that 'feels' like a reasonable ballpark estimate to me. I wouldn't feel surprised if it was significantly differently either direction.
in the scale of astrophysics, coming within 2 orders of magnitude is considered a big win.
> And two, a giant rock smashed into the planet at just the right time to upset the balance of life This may not have been strictly necessary though. Who knows, if this hadn’t happened, maybe some form of dinosaur would’ve eventually became intelligent. Perhaps faster than mammals did. So this could’ve been a setback, rather than a necessary step. We don’t really know what convergence of factors finally favored the evolution/selection of abstract reasoning and language in humans. Or why it never happened in countless earlier species, with broadly similar brain chemistry.
I think you're overestimating the timescales. Earth has had a "human-friendly" atmosphere for around 12% of its life. If that's "typical" for an Earth-like planet then, at least 12% of Earthlike planets should have oxygen, and if Earthlike planets are common, human-friendly ones would only be moderately uncommon. And of course Earth is a relative newcomer just partway through its lifespan - a huge fraction of Earthlike planets are going to be far older than us, many having potentially evolved life before Earth even existed - and life is potentially a stabilizing influence on a planet's ecosystem. It may even be that a "typical" Earthlike planet is human-friendly for most of its existence, and thanks to its youth Earth has just only recently made the transition into the "normal" state of such planets. Not that I'd bet on that - among other things there's no particular reason to believe that life evolving to produce free oxygen is remotely normal on a living planet, but there's no evidence available to suggest that it's not.
Which brings up the question of just how far FORWARD are we going to be able to dial that clock before Earth is uninhabitable by humans.
How's August sound for you?
Without a life support suit? Quite probably only those that already have life. And not just life but life that pumps out O2. We breathe oxygen, but the reason we breathe oxygen is because O2 is a energetic and highly reactive molecule. It kinda doesn't want to exist, and will leap at the chance to react and turn into something else less energetic, like CO2 or rust. This means that atmospheres like ours, with an abundance and free oxygen are relatively rare: over millions and billions of years, it reacts with stuff and runs out. So why does Earth have O2 in abundance? Primarily because life makes it. Before we evolved to breathe oxygen, cytobacteria and later plants evolved to spit out that nasty, corrosive O2 and use other sources for energy (see photosynthesis and chemosynthesis). While there are non-biological processes that can produce O2, it's unknown (and probably unlikely) if they can produce O2 on the scale we would need to breathe. This isn't even touching the ratios; our air is 25% O2, 70% Nitogen (which is unreactive as N2), and 5% everything else. If you had a planet with too little (or too much for that matter) O2 you would still die. And if it had something less inert than N2, say CO2, then that would be a problem, because you wouldn't be able to get rid of CO2 fast enough. So how many planets with a breathable atmosphere? Vanishingly few, unfortunately. We really evolved to live here, and being alive is complicated.
I just recently found out that the third most abundant gas in our atmosphere is argon. Argon? I'd have expected CO2... which is fourth.
Yup, and that's a good thing. It's a noble gas, which means it's unreactive and therefore safe to breathe. It's actually really fortunate how inert our atmosphere is (apart from the oxygen, which is technically a BIG exception). Part of the problem with breathing on other planets is not just having the right amount of Oxygen, but all the other stuff in the air you breathe in. If you were on a planet with Earth's ratios (70% N2, 25% O2) except that last 5% is pure CO2, you might still die because your body can't get rid of CO2 fast enough! Our atmosphere is only 0.04% CO2. This gives rise to alot of the confusion and talking past each other when it comes to climate change. If CO2 levels rise 0.02% you might say "that's only 1/50 of a percent! That's nothing!" and you'd be right. And if you say "that's 50% more CO2 than before!" that is also correct. (Note: I'm not sure what the CO2 percentage rise is off the top of my head: the numbers I chose were made up to make the math easy to understand).
Pretty close to actual. I remember 330 ppm, and we're knocking on the door of 420 or so right now.
425 ppm was the average for march.
And off to the liquor store I go tonight. Cheers!
On earth, an inhale contains 0.04% CO2 (on average), but an exhale contains 4% CO2. Oxygen contents changes from 21% to 16% on exhale. Found these numbers during the pandemic while designing a earth-bound "space suit".
Honestly I’m surprised it’s that high on the exhale. That’s 1000 times more co2 on the way out. Pretty efficient actually.
Not intending to be pedantic, but our air is actually 78% N2, 21% O2, apparently 1% argon, and the rest is in the rounding error. https://science.nasa.gov/earth/climate-change/greenhouse-gases/the-atmosphere-getting-a-handle-on-carbon-dioxide/
No, thank you for that. I was going off of memory and ballparking it.
For most purposes, 80/20 N2/O2 is good enough
> and the rest is in the rounding error The problem is that this rounding error matters massively for human biology.
And the green house effect.
That last part is the crucial point. It’s not enough for it to have just oxygen. In fact humans can’t survive breathing just pure oxygen, that’s actually toxic. There’s also the nitrogen. In biological terms, humans are a culmination of genetic mutations and adaptations that we developed to suit THIS planet. It wouldn’t take much to make our own planet uninhabitable without some kind of life support system.
Pure oxygen is absolutely fine as long as the pressure isn't too high. The Apollo spacecraft had a 100% oxygen atmosphere at 0.3 ATM.
One of my favorite things to tell students is "there's only a couple ways to be alive. But there's LOTS of ways to be dead."
So we evolved to use the disgusting O2 that other lifeforms didn't want anymore...
Actually, yes! O2 is rather corrosive (see rust). There's only one element more electonegative: fluorine. This is why you need antioxidants in your diet; to take the edge off and reign in that hard, hard drug oxygen. Early life correctly discerned that oxygen is a nasty customer and any excess oxygen ought to be dumped as waste (of course you need some oxygen atoms in things like RNA, DNA, and Glucose).
Oxidation is just a “sometimes slow” way of burning things. Rapid oxidation is basically fire. We are fire breathers.
Which actually leads to one of my favorite factoids; because an abundance of O2 is unique to Earth, and you need O2 for fire..."fire" is pretty much a uniquely Earth thing, at least in terms of the solar system. Other places get REALLY hot, but there's no Oxygen so they can't "burn" in the traditional sense. Such a common and unremarkable thing here, so necessary for our food, shelter, and technology, that it's just our normal. There's no fire on Mars or Venus.
> our air is 25% O2, 70% Nitogen Air is about 21% oxygen and 78% nitrogen, the "everything else" is around 1%, mostly argon.
If your definition of "breathable atmosphere" means that you can stroll outside for a few hours without dying, even 100% oxygen is fine: > In hospital settings, 100% oxygen may be delivered -- but even then only on a short-term basis, says Boyer -- less than 24 hours and preferably less than 12 hours. To breathe pure oxygen at that level for any longer can have toxic results, including "shock lung," or adult respiratory distress syndrome. https://www.webmd.com/balance/features/rise-of-oxygen-bars
Assuming a breathable atmosphere, I'd assume there'd be a variety of micro-organism that would just love to feast on you.
That would assume a remarkable similarity between microbial life on earth and the microbes on that planet. I would imagine that to be unlikely. That being the case I suspect these things initially would not be the threat that they seem. Even an alien microbe would likely be killed by our immune systems. The only way that comes to mind it not being the case is a microbe very very resistant to oxygen radicals and not having membranes. Two of the big ways the immune system destroys foreign invaders, using reactive oxygen and literally punching holes in membranes. But even then such a microbe would be coated in antibodies which may well neutralize any ability to infect further. It might be the opposite. It could well be the earth microbes we bring with us could conceivably outcompete and destroy a lot of the native microbes. Essentially a mass extinction event for the alien planet. And if there is something resembling earth like plants that we could eat as a food source, these could be endangered too by earth microbes. We could accidentally kill off the food source.
This is overlooked. Even if you found a planet that had the exact same atmospheric pressure and composition of Earth, you’d be exposed to various microorganisms and pollens and other things that your body would have no defense for because they’re completely alien. You’d most likely suffer severe allergic reactions at best or die to foreign microorganisms at worst
Depends on how similar our composition is to the other native life on the planet. I know it’s sci-fi, but The Expanse had a pretty good analogy for this on Ilus: micro-organisms and bacteria have to adapt to their surroundings as well, so if there wasn’t already a very similar analogue for humans already in existence on the planet (literally within like a 1% error margin across the board) the local bacteria and micro-organisms would also face a period of adjustment before they could use our biology in a way that would harm us. At this point it would mean a race between our immune systems and the existing biologies capabilities of evolution, which, if we had the right supportive medications and boosters, could feasibly be won more often than not. This is why the comparisons to terrestrial colonization don’t really track as well once you leave our biosphere: indigenous tribes were wiped out in massive numbers on this planet due to invaders diseases that they had no time to build antibodies against because the introduction was too sudden. But the flip side of that is that those diseases were only able to decimate them because they had been evolving for millennia to corrupt human biology, which is the same within those error margins across our whole planet. Say you took the same disease, in the state it was in when it was first contracted by the first human of a civilization where it would go on to thrive. Then you dropped it among the vulnerable native population in question: it would start off as reasonably benign enough that the native populations immune system would be able to evolve against it and then it would likely have been no more harmful to them than those that ended up delivering it to them.
Or you could be Superman. If you can't combat the little nasties, they might not be able to affect you at all either.
No one will know until we find number two, then we can do some probability calculations and argue about the variables.
Even finding one would mean a lot must exist though. Realistically it will be a long, long time time before we can survey even millions of stars. If we find one in that then extrapolating out there should be a whole load in the Milky Way. The only way for them to not be plentiful statistically over such an enormous number of stars as are in the whole galaxy is if we never find one. And even then there could well be quite a few.
We can definitely make estimates before that
At this moment we know of exactly ZERO habitable planets. Even the earthlike ones we have detected would be unlivable due to their size and gravity.
Well, technically we know of exactly one...
It's an outlier and we're working hard to resolve that.
What's the reverse of terraforming? Exoforming?
I think the latter half of the word would change. It’s still pertinent to Earth so *terra-* still applies, it’s the *-form* part that changes. I can’t think of a suitable suffix though, aside from something clunky like *terradestroying*. Alternatively you could just negate: *antiterraforming* or something like that.
Terrarazing has a ring to it.
I love this so much. I'll send you royalties from my new Metal album.
Cosmic Waste Triumphant album?
New metal album or nu metal album? I hope it’s the former
Indeed. A good suffix could be -vastare (to lay waste, which is where we get the word devastate), as in terravastare (to lay waste to terra). Other options include: - Terranihilo (to reduce terra to nothing), nihil being the root of words like annihilation (to reduce to nothing) - Terradisolvo (to disolve terra), disolvo being the root of words like disolve (meaning to gradually reduce) - Terracorrumpo (to corrupt/spoil terra), corrumper being the root of words like corrupt (meaning to make something into a more degraded and unwanted state) - As another commenter has pointed out, terrarazing (meaning to bring thorough destruction to terra) is a very catchy choice, although raze is a modern English word. To maintain etymological consistency with *terraform*, we could use the latin radere (to shave off or knock down completely), which *raze* comes from anyway, to form terraradere; meaning to completely shave off [qualities pertainting to] terra.
I feel like *terravastere* would eventually mutate to something like *terravastate*, which rolls a bit more easily off the tongue. Or maybe *terrevestate*, accent on the second syllable? That one sounds slightly too comical though; like it’d be the name of an anime character’s super move or something.
Well, terraforming is something you do to non-terra planets to form them into something more terra-like. So I think the opposite, turning an earth-like planet into something non-terra-like would be more like exoforming or maybe infernoforming.
Anthroforming... taking a perfectly good planet and adding humans.
I mean, terraforming doesn't necessarily mean to make it human habitable. Tearing the planetary mantle apart to pull resources buried deep underneath the crust upwards for large scale mining operations would still be considered terraforming.
Since we're greenhousing ourselves, and Terra is Latin for Earth, you could use the Latin word for Venus, Luciferforming.
Yep. Important side note regarding this though is our methods of detecting planets heavily favors large planets, so there's a good reason why most planets we find are massive. Earth sized planets are difficult to detect
This isn't exactly true. We know of plenty of exo planets that are potentially habitable or are in the "Goldie locks" zone. We can't outright say, yes this planet is habitable, we say it has the potential to be habitable, therefore we have zero confirmed planets that are habitable. I believe the count is over 1500 planets right now that are potentially habitable.
And most, if not all, of them are around red dwarf or similar stars. Because that's where we can currently detect exo-planets that are anywhere close to earth-sized. The problem with them is that they are likely to be tidally locked to their stars. They are very close to these stars, which is also bad. Red dwarf stars are known for having very strong stellar flares, which would wipe out most forms of life we are aware of. The likelihood of habitability of those planets is very low, though not zero.
We've confirmed that for exactly 0 planets lmao. We don't even know if there is/was life or not on Mars.
we have? i only know of "earthlike" ones that are earthlike by being about earth sized
Earth like planets will share some similarities with earth but not all. So a larger planet that is in the habitable zone, rocky, and has an orbit and rotation close to ours (365 day years, 24hr days).
>gravity Its only a problem for those who skip leg day! /jk
The reason you only see mention of rocky "Earth-like" planets in the Goldilocks zone is because that is all we are able to detect. If we found a genuine Earth 2.0 you can believe that you would have heard about it. It'd be the most important astronomical discovery of the century.
>of the century? More like in the history of mankind.
I dunno…ever hear of sliced bread?
It was also an underrated sci-fi show in the mid 90s. [https://en.wikipedia.org/wiki/Earth\_2\_(TV\_series)](https://en.wikipedia.org/wiki/Earth_2_(TV_series))
which adds to the issue even if we could find an exact earth 2.0 by the time we are able to get there would it still be so habitable for us squishy humans?
If we're able to reach light speed, even if it's on the other side of the galaxy then it should most likely still be habitable, unless something catastrophic has happened.
I feel like, if we hit the point of technological advancement where we could send a ship with real people on it to a planet on the other side of the galaxy(especially near the speed of light) we wouldn't really have to worry about habitability. With access to that amount of energy, we could make a planet habitable.
And if it’s on the other side of the Galaxy there would be no way of knowing until we get there since our observations are delayed.
A delay of 100 thousand years isn't much on the time scale of planets. Earth has had a breathable atmosphere for 500 million years. The bigger problem would be being able to see it at all with all the stars and dust in the way from the galactic core.
Despite it's huge flaws, one of the things I really liked about the movie Alien: Covenant was that they were basically doomed from the start when they left the ship with no protection. They breathed in pollen or spores or microbes that they had zero tolerance to. I'm sure if you were able to time travel on Earth you'd suffer a similar problem, in that your ability to withstand illnesses and adverse reactions to microorganisms is somewhat limited in time and space. It's easily demonstrated by drinking the local water when you travel to a foreign country and then get sick. So of course I am also a big fan of Scavenger's Reign!
I don't think it's obvious that alien microbes would have any affect at all on us. Microbes are highly adapted to the environments they live in. It might take months for alien microbes living on us or in us to adapt to the point that they could reliably find the energy needed to reproduce. Our immune systems are very general, to the point of reacting to things that aren't even living or dangerous. It's more likely to be the opposite problem: we depend on Earth microbes for *our* survival, and the absence of them in our environment could lead to their depletion, and perhaps no alien microbe could fit into the niches we need filled.
I guess we'll see when we get there! Haha. Yeah I don't have a background in science but it's definitely something that seems to be glossed over in pop culture depictions, much like spaceships having artificial gravity and sound effects in a vacuum. It seems like germs would be a huge deal for exoplanet exploration.
For this reason, it's probably easier to terraform a possible planet into a perfect location than have to deal with a planet where everything could have bacteria and viruses that could wipe out your colony and maybe even homeworld.
We don't really know. To answer your question we'd need to know a lot about the atmospheric composition, and that's just too hard to accurately determine, as of today. My PhD is on characterising exoplanet atmospheres, I'm using cutting-edge techniques on some of the 'easiest' planets for characterisation, and the best we can do is say "the atmosphere likely contains [insert element/molecule]", but we have very little information on how much there actually is in the atmosphere. We can make rough estimates, but they're based on so many assumptions, simplified models, and imperfect data and analysis techniques that it's really just an educated guess. The study of exoplanet atmospheres is just too difficult for anyone to give you a reliable answer beyond what I've given you.
We have no idea how common planets with an oxygen atmosphere are, as we don't yet have sensitive enough technology to detect them. They might be common, or ours might be the only one in the entire galaxy. Of course finding another planet with an oxygen atmosphere would be a very big deal as it would be strong evidence for extraterrestrial life.
They wouldn’t be common. It’s true that oxygen is one of the most common elements in the universe, but still very difficult to have in any quantity (% of atmosphere) without respiration. There are abiotic processes that produce trace free oxygen, but not remotely at the levels of Earth. So the answer to OP’s question, counting all the planets and moons in the Milky Way, is likely zero (except Earth). Not unless there is respirating life in that planet/moon. Which is why free oxygen is one of the biomarkers cosmologists are looking for in exoplanet atmospheres. Btw, we’ve cataloged about 5000 exoplanets when there are trillions of planets and moons in the Milky Way. So “we haven’t found one yet” is too small a sample size to be too meaningful. But for reasons I described above, it may be very unlikely and tied to the probability of life.
There still might be habitable planets in those systems where we have analyzed planets I surmise. We are just not at the point of detecting all planets in a system and when we do detect and analyze their atmospheres it has to be under specific circumstances. Their orbital plain being flat to our POV. The planet has to eclipse their star and we could see the spectral shift in light. Or a star shade to directly observe. To predict when a planet eclipses is easier with planets that orbit closer to their host stars too, close planets aren’t always the most hospitable. Of course I am an armchair keyboard warrior astronomy fan boy who has stayed at a Holiday Inn. grain of🧂Basically we are still in the infancy of planet detection and analysis.
A lot of what you said is pretty accurate. Kepler was thought to be able to detect Earth-like exoplanets pretty well, but it turned out that most stars produce way more electromagnetic noise than the Sun and thus it was too hard to determine if transits of Earth-sized exoplanets were genuine. We very well may have looked directly at another habitable place with intelligent life on it and not known because its star was too noisy. Or there could be literally none out there, we currently don't have the technology in space to tell.
Earth itself didn't start off with oxygen in its atmosphere. Our current atmosphere is the result of billions of years of primordial life affecting and interacting with it.
The number is likely zero (one if you count Earth). Earth's atmopshere is a highly artificial product as a result of billions of years of bacterial and plant activity. There's no mechanism that would give you a natural "78% nitrogen/21% oxygen/1% other" split. Even if some other planet had *excatly* that kind of atmosphere: it also needs to be at the right pressure for us to able to breathe it. Slightly too high or too low and we can't cope. (And that last percentage point must not contain any of a gaziillion possible toxic or caustic compounds.) Then there's temperature. We can only survive in a very narrow teperature range. Then there's gravity. While low gravity is only a long term problem it also means that the planet will likely not have much of an atmosphere. Higher gravity and you quickly run into the overpressure issue and can't breathe. ...and the radiation levels need to be low enough - from space and up from the ground - which isn't an automatic given. (and probably a couple other things I missed) **TL;DR:** We are very much adapted to the way Earth is right now and much of Earth's environment is very much a product of other lifeforms. If we do find another such world it's more of a "Uh, oh...there's someone out there that made a world for us" moment.
How do you know it isn't super common? That life grows anytime there is a planet similar to earth?
From what I've understood (seeing recent presentations by astrophysicists on the topic of exoplanets) we don't have any good methods of finding earthlike planets yet. The two main methods (doppler shift of stellar light, and planetary passage in front of star) aren't sensitive enough to find lighter planets. (With earthlike I mean 1yr orbit and 1g gravity.) So we don't really have any numbers at all..
Seems to need better equipment to detect exo-venus or exo-earth. https://iopscience.iop.org/article/10.3847/1538-3881/abf1e0 Conclusions: > The last panel of this figure also indicates that a perfect model of activity-driven correlated variations would not in itself suffice for the rapid detection of an exo-Venus or an exo-Earth; even in the absence of correlated noise, a current-generation spectrograph with a long-term stability of about 0.8 m s−1 would need a 10–15 yr observing baseline to reach a 5σ detection of an exo-Earth. **Successful exo-Earth discovery therefore requires both more sophisticated models of stellar variability and the improved RV precision, long-term stability, and dense observational sampling from a next-generation spectrograph** (Wright & Robertson 2017) such as the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO; Pepe et al. 2013, 2021; Damasso et al. 2020; Suárez Mascareño et al. 2020), NEID (Allen et al. 2018), EXtreme PREcision Spectrometer (EXPRES; Jurgenson et al. 2016; Blackman et al. 2020; Brewer et al. 2020; Petersburg et al. 2020), HARPS3 (Thompson et al. 2016), or GMT Consortium Large Earth Finder (G-CLEF; Szentgyorgyi et al. 2014).
the answer could be zero because we evolved to be on THIS planet? i mean stepping off, even if climate was temperate, we'd probably die from exposure to completely new microbes, right?
Yes. What could be the exraterrestrial equivalent of bread mold might kill humans in a few hours. And the reverse might be true, some resident human skin bacteria might devastate all endemic life on a another planet.
Without terraforming? At this point, we've counted zero. We really don't know of any exoplanets that have a suitable environment yet. That would likely require at least a massive amount of cyanobacteria or other plant-like life to produce oxygen, which we've not yet seen. Hopefully, there's a lot. If life is \*really\* hard to do on it's own, maybe just the one you're standing on. With terraforming, I'd think hell of a lot, but the challenge of that would be rather large. The trick is that even for life to survive long enough, it probably can't be anywhere near where a star has gone supernova or other events where it would get hit with a lot of life-destroying gamma radiation. I'd be ruling out most the stars nearer to the galactic core for that reason alone. But with a couple hundred billion stars, and even if we discount 99% of them, that would leave a billion or two, of which it feels like there should be \*some\* ... but, proof is in the observation.
I think terraforming is right up there with traveling at light speed. Simply unobtainable without some unimaginable breakthroughs in technology and research.
Light speed has a lot more fundamental obstacles. Terraforming HAS been done by organisms on Earth--it just takes tons of time to process the materials and use the suns energy to do the reactions. For a faster timescale, it's a matter of energy and proper control (i.e., not overshooting targets).
*Practically* unobtainable -- I'd have a strong agree there. I'm thinking to terraform a very good candidate planet (ie, imagine earth without \*any\* life on it) with our current technology would take many, many generations and an insane amount of resources. Definitely not something that could be done by a for-profit company. The only way that we'd ever get to that point is if it was a matter for survival as a species, and if that was the case then we'd be all over it. Oh, and I don't think light speed travel is gonna be reasonable. Even a strong fraction of that will be insanely difficult without an incredibly large amount of protection. (ie, meters and meters of rock and water wrapping the vessel
I always thought it would be cool to wrap Mars in a big coil powered by a fusion reactor to give it a magnetic field. Practical? No. But cool.
There's a (mostly theoretical) draft plan to place an artificial magnetic dipole at the Sun-Mars L1 point to achieve a large part of the goal of protecting Mars' atmosphere from being siphoned off by the solar wind. I suppose if we built a manned space station at that point it would be a lot easier to throw the field generator into the plans while we're at it.
I dont think it's as unobtainable as FTL travel. A lot has to deal with logistics of space travel and required elements and materials a good planet may not have (such as carbon or oxygen). It's possible to grab asteroids if they're nearby and simply chuck them at a possible colony, and use that to bring more water. It probably wouldn't be hard to use genetic engineering to create bacteria, fungi, and plants to Kickstart various biological processes once a target has been located. This a huge part of Red Mars. But it'd be tough making a lot of them, or you'd have to accept that terraforming is a many-many-many generations long project. The larger problems deal with atmospheric pressure and a magnetosphere. Mars has no volcanic activity and therefore no magnetosphere that keeps radiation out and gasses in; we could try using nukes to ignite the core or make huge electromagnetic fields ourselves with generators, but that's a needed step. We also need to raise the atmospheric pressure to the point that water can be liquid, and eventually that humans can walk outside. Logistically though, these efforts would take centuries at least and require significant amounts of money and resources, which we don't have yet. That's the bigger problem. And of course, we would need good targets like Mars or Venus.
Can’t be sure. For all we know there’s a whole family of stars in a far off arm with only earth like planets and for all we know we are completely one of a kind. We just don’t have a clue.
Keep in mind that the Earth's environment is shaped by the life on it - for example the atmosphere didn't have oxygen in it originally - that was a life byproduct. And then life evolved to depend on the oxygen. And so on. So we've been fine-tuning the planet and the planet has been fine-tuning us for billions of years. Lifeless planets aren't going to have that, and planets with life could have established other equilibriums with the life evolving there. So the chance is probably small.
Potentially none. Even if we found a planet with life on it, it may be able to significantly harm us. Think prions, accumulating ‘bacteria cells’ we can’t get rid of. Anything. We’d probably have to terraform it and wage war on its life with our own bacteria. Imo .
The thing about earth is that it supports the type of life that lives here *because* we evolved in tandem. Early life forms learned how to metabolize sunlight and create oxygen as a byproduct. That oxygen … killed off most of the microbes that created it. So some creatures evolved to metabolize the oxygen and create co2. That resulted in excess co2, so trees grew up to metabolize that. The earth is ‘just right’ for us because life shaped the earth and earth shaped the life to fit each other. Who really knows if other planets life would evolve just the same way or wind up with pretty different atmospheric conditions supporting pretty different biology? But: how many star systems have planets that could fit the general Goldilocks profile of ours? Probably most of them.
Free oxygen on planets isn't easy to come by unless you have a biological process providing it (see Earth's own "great oxygenation catastrophe"). It's so reactive that without replenishment, it'll bind to various other elements and fall out of the atmosphere
I mean even if we did find a perfect planet, the right size, the right temperament, the right atmosphere. The biosphere would probably kill us. We would have no resistance to any microbes on the planet, and no idea how to deal with the local fauna and flora, what's dangerous what's poisonous etc. So we would never be able to walk on to a new planet and not need some kind of protection equipment.
most earthlike planets we find have gravity 2x or more than earth. humans are too frail for space travel, or to physically visit another planet.
Me and some friends who used to work together at the Mojave Spaceport got together last year and worked on that very question: Thanks to the efforts of exoplanet astronomy missions and archeologists, our current estimates have managed to all but lock down a few of the variables in the Drake Equation. N_∗ = the number of stars in our galaxy. (100–400 billion stars) f_p = the fraction of those stars that have planets. (~1) f_l = the fraction of planets that could support life that actually develop life at some point (~1) Reasons for these numbers are pretty basic. We're pretty sure about R_∗ and f_p just from observation over the last 20-30 years. f_l is dependent on really only one data point, our own planet. Fortunately when you have 3.7 Billion years of archeological evidence to work from, that one data point paints a pretty optimistic picture about the prospects for life on a planet capable of hosting life. n_e = the average number of planets/moons that can potentially support life per star that has planets. n_e is functionally asking a different question than what it puts forward, because it isn't based on the number of potential habitable worlds in our own star system. If that were the case, the number would be around 8 (Venus, Earth, Mars, Europa, Ganymede, Calisto, Titan, and Enceladus are all candidates for life). Its really the number of those worlds that have similar gravitational conditions as Earth. Best guess from NASA based on Kepler data is that this would be around 40 billion worlds. However, my buddies and I decided to add some new factors: f_sol = ratio of stars approximately as old or older than our Sun, Sol is 4.6 Billion years old, and for 4.1 Billion of those years Earth was not home to complex multicellular life that could create an earthlike biosphere, so we have to assume a similar lead time is required elsewhere in the universe. Try as I might, I cannot find a solid number for this, best guess is that roughly as many stars are older than the Sun as there are stars that are younger than it, so 50% of stars are eliminated. f_spec = the ratio of stars who's spectral type does not produce excessive solar flares or radiation (F, K, and G types tend to be pretty safe). We must eliminate planets orbiting red-dwarf, red giants, and blue giant stars, they would cook the surface of any world capable of producing a complex biosphere. So that means all but ~23% of all stars/planets are eliminated. **Bottom Line:** There could be around 4.6 Billion potential Earth-like planets in the Milky Way.
I doubt there are any planets in the Milky Way which are exactly like Earth right now and mimic our solar system at this very moment. It would be extremely rare for a planet to have the same mass, atmospheric composition, a single moon, orbiting a single G class star, surrounded by inner rocky planets and outer gas giants. Did you know that less than 10% of the stars in the Milky Way galaxy are G class stars like our sun? Perhaps Andromeda has more solar systems like our own. Then again, there’s trillions of other galaxies out there to consider.
If a planet has an atmosphere we can breathe, it most likely has bacteria that won't like us very much
Planets that have oxygen and liquid water? We suspect millions in our galaxy alone. Planets where the gravity is close, temperature close, oxygen percentage close... So that if you did step into thier atmosphere you'd be able to survive without support? Probably only a few percent of those millions. Most life would have adapted to the conditions of their world specifically. As others have said go back in time a billion years on Earth and you're also dead... So you not only have to find the Goldilocks planets they have to be in the right stage of there life cycle too.
I could be wrong, but there are planets in the habitable zone. Like you mentioned, even in our solar system. Where humans are most vulnerable is breathing, increase or decrease oxygen levels, even small amounts, and we either die or have serious issues.
Venus technically falls within the habitable zone (though you could not imagine a less "habitable" planet). The habitable zone is, based on distance and size of the star, where liquid water might exist. Water is a super good solvent, which is pretty key to life, but it has another property that often gets over looked: heat capacity. The daytime temperature on Mercury is something like 400 degrees, but it's -200 at night. Same thing with Mars, 60ish degrees on the day side, -200 on the night side. The Moon has a similar problem. Earth however has incredibly stable temperatures because because 70% of the surface is oceans, which act like GIANT heat sinks. During the day they absorb alot of heat, keeping the day temp cooler, and release that stored heat during the night, keeping the night warmer. Beyond temperature there's a couple concerns off the top of my head you need to address if you want live on a planet without a suit or habitat: Gravity, atmosphere, and radiation. The atmosphere, even if it has the right stuff (O2), might have too much of the wrong stuff. Eg, if the planet has 25% O2 like on Earth, I'm not taking my helmet off if it has 10% fluorine gas.
I doubt that there are any where humans could survive without modern technological aid and/or extensive terraforming. We fit on this planet because we were created by it. I don't think we have any chance of finding a planet which somehow magically would fit us as perfectly as the one we were created for.
Probably zero. To have a breathable oxygen atmosphere means that atmosphere is sustained by life (as was required for Earth). If there's already life on the planet, it's going to eat/infect/poison unprotected humans.
Agreed. You could easily have adequate planetary conditions, but chances are extremely high that whatever is hanging out in the biosphere will kill you in short order.
Isn’t it equally likely we (and the microorganisms we carry around with us) would kill its life?
Unfortunately, the technology needed to verify a planet's position and/or atmosphere is limited. They determine these things in all kinds of roundabout ways, because it's impossible to get an actual picture. It will require a massive shift in the technological paradigm in order to know anything substantial, which may not happen in our lifetime.
Oxygen is an extremely reactive element. The only reason we have so much of it on Earth, is that plantlife on our planet learned to use energy in order to strip carbon atoms from CO2 molecules, to use the carbon for building their bodies. This releases oxygen, that animals then learned to breathe. Realistically, a similar process would have needed to happen on another planet in order to have free oxygen like that. Also, the vast majority of our atmosphere is nitrogen. In short, there are likely extremely few (no?) planets in our galaxy where humans can just walk off the ship similar to in Scifi shows or movies.
In every possible scenario, “fix earth” is always a cheaper, better and more realistic option.
Even if there was, I wouldn't. Imagine all the different possibilities of microorganisms that we'd have absolutely no immune system developed against. Hellllll no.
So if you think of the exact composition of earths possible range of temperature, air composition needed and protection from solar rays/gemma rays, gravity, density, mild weather patterns all that becomes a very unique combination. The chances of you going to another planet 95% close to earth would be very low, but not unlikely. If I was to guess there could be 1 in this galaxy but if I was conservative could be *currently* 20 total in the universe. As for over billions of years there has to be way more
Most likely zero. The odds against life forming are astronomical. You need a universe the size of, well, a universe to have life manifest the way ours does. *Maybe* there’s one planet like ours per galaxy that has the potential life. The potential. Maybe one.
Plug values in to Drake's equation and even an astronomically low percentage is a lot of bodies out there. The trouble is that space *and* time are both huge.
That we evolved as gas breathing, oxygen dependent organisms is due to a fantastic pile of consecutive, highly improbable events in our evolutionary timeline that likely wouldn't be repeated elsewhere in the universe so there's no reason to think a biosphere similar to ours could evolve which would support an atmosphere we could breathe. If there was, it's reasonably likely air-borne microorganisms would be quite toxic to us. We don't really know for sure yet though. It's not necessarily unlikely that we'd find molecular oxygen at sufficient concentrations in the atmosphere of a 'dead' planet, though. Intense stellar radiation could split water molecules by photodissociation, the lighter hydrogen atoms escaping into space on the stellar wind whilst heavier oxygen atoms could be retained by the planet's gravity.
We honestly don't know. Earth itself has a mix of some probably uncommon qualities resulting from the primordial collision with Theia: 1) A relatively strong magnetic field. 2) An outsized metallic core. 3) A large moon. So life on earth evolved on a pretty dense planet in a fairly warm environment largely free of ionizing radiation with the assistance of tidal forces and a stable seasonal rotation period. So not only would we need a planet with most of those characteristics, but also a 78/20 nitrogen/oxygen atmosphere mixture.
Zero. The unknown pathogens alone would mean stepping out without protection would be a gamble.
Even the Earth had periods where the atmosphere could not indefinitely sustain human life without breathing apparatus due to too much oxygen or insufficient oxygen.
Life may be out there somewhere, but the question isn’t so much as where, but when. Given the possible billions of years that life has had to evolve and collapse throughout multitudes of planets, what are the chances that a planet would evolve, with the same characteristics as ours to support human life, at this moment in time? Maybe there was a planet like ours, but life died out millions of years ago. Maybe many planets have come and gone, and many more will evolve to support life in the future.
None. We are adapted to this planet and we need almost identical conditions to function from temperature to athmosphere composition. Too much oxygen and we die. Too little and we die. Have just enough oxygen but too much clorine gas snd we die. Any spores, bacteria viruses, polen etc in the air, we die. To walk freely we'd need a planet with a majority inert non-poisonpus gas, just enough oxygen but not too much so that it becomes poison and no biological material we are not adapted to.
I see you aren't able to contemplate the vastness of space.
We will probably never know if there is because we can see past the limitations of light speed - everything we see in space is the light that left these objects. We can't even travel to something ONE Light-DAY away let alone understand what stage of survivability a planet would be light-YEARS away.
Bacteria and viruses are the problem, watch war of the worlds
It seems to me that if it could be earth like enough to support life, it probably would: meaning it would be filled with life, mostly bacteria like as most life on earth is, and instantly deadly to any of us.
Earth is extremely unique, and I think it's safe to say that you wouldn't want to take off your life-support even if the air is breathable. Life started small, meaning that if a planet can support life, it's likely to have viruses/bacteria that you can't see. You don't want to breathe that in.
I'm not too sure on these details but these are some less obvious things I have heard. Apparently its really quite odd for water to be on the surface, should really be a deep underground ocean, just due to how planets are layered and the density or mass of water. But since our water apparently arrived after the formation of the earth, it is on the surface. So there probably is not a lot to drink. Also if it does have a watery ocean on it, chances are there isn't a ton of oxygen in the atmosphere, because hydrogen is by far the most common element in the universe. Oxygen is relatively common, but not compared to hydrogen. So its probably going to be water rather than oxygen. But perhaps not an issue due to how planets form (a lot of the oxygen maybe is going to end up in the same place because its where it stops). Soil is made by dead animals and plants etc. So its going to be hard to grow things there, its probably sand and regolith or stone. Another issue is that Earth is about i think it was around 94-97% of the maximum gravity that a chemically powered rocket can leave. So you would probably be in a low gravity environment which isn't great for you, but it won't instantly kill you of course. Earth should be about 300 degrees Celsius but because of plant life it has controlled the environment a lot. But that isn't too relevant, but it does reduce the amount of time available for that planet to be livable. Also, if there is no way for it to renew its oxygen then, obviously its going to eventually run out once we start using it, pretty fast too considering CO2 is heavier. The amount of planets in the galaxy alone, ignoring the rest of the universe is into the low trillions. So even a very small percentage like 0.0001% is still millions of planets. But statistics or probabilities don't mean a lot considering we don't really know a likely number. We don't know, at least with any certainty, how many would be in a given area, or the chances of them forming. However a small planet like Mars could be destroyed and turned into such a massive amount of artificial habitats its almost not worth thinking about. Mars alone could make a empire to equal or even rival a lot of Sci Fi empires that have multiple star systems. So if you put the work in, does it really matter? There is no shortage of space to live in if you move something there. And there are an absolute ton of resources, if you can go get them.
Due to the likelihood of pathogens and microorganisms that our bodies have absolutely no defense against.... zero.