I fell way behind on my science and space exploration research last year. I now have a tall pile of to-be-read books and papers in my reading room. But I’m now starting to catch up, beginning with this paper on the atmospheres of Earth-like planets.
As explained in this article from the Planetary Society, the goal of this paper is to start creating a guidebook for finding planets that might be home to alien life. And based on what the paper says early on, it sounds like there are plenty of “habitable Earth-like planets” out there to be found!
If we’re looking only at red dwarf stars, which are the smallest and most common of stars, about 30% of them should have a habitable Earth-like planet orbiting them. And between 5 and 20% of orange, yellow, and yellow-white dwarf stars should have habitable Earth-like planets too. Our own Sun, by the way, is a yellow dwarf star.
Statistically speaking, this means we should find another Earth orbiting a red dwarf within only 2 parsecs of us. And there should be another another Earth orbiting an orange, yellow, or yellow-white dwarf within 6 parsecs. I feel like that’s surprisingly close, at least in the grand scheme of our universe.
Except when astronomers talk about Earth-like planets, what they’re actually describing does not necessarily sound much like Earth. Any planet that’s about the same size and mass as Earth can be called Earth-like, and by that standard Venus is about as Earth-like as any planet can be, aside from Earth itself.
And when this paper talks about habitable Earth-like planets, I’m pretty sure all the authors mean are planets within the habitable zones of their parent stars. But just because a planet orbits within a habitable zone does not mean that planet is truly habitable. Again, look at Venus.
So when we do find a “habitable Earth-like planet” within 2 or 6 parsecs of us, how will we know we’re looking at another Earth and not another Venus? That’s a tricky question. Maybe it would help to think about the problem from a different perspective. You see, while we humans are having a really difficult time finding alien life, the aliens may also be having a very difficult time finding us.
More on that in the next post!
Planet Pailly 
I’ve come to the conclusion that either they’re too far away, are at the same or less evolutionary development position as us, or they’ve been, had a look, thought ‘nope!’ and gone looking elsewhere.
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I agree with those points, especially your second point. Odds are even if we do find life out there, it will probably be at a different stage of evolutionary development. Earth spent far more time without humans than with us. Earth also spent more time without multicellular organisms than with them.
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I can see microorganisms being fairly ‘common’ because they seem to turn up everywhere from inside glaciers, to the bottom of the deep ocean, to geysers, but anything multicellular must be incredibly rare. Time, the right conditions, environmental stability, so many conditions are needed, as you said Earth has been longer without multicellular organisms than with. But it’s nice to dream that out there somewhere there might be another relatively intelligent species having the same conversation.
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If by “aliens” we just mean life, then I’ll be surprised if they’re not within a few dozen light years. Of course, the difficulty will be in how to detect that kind of life. The presence of large amounts of oxygen seems like it would be a good indicator. Even though there are abiotic processes which can lead to it, they don’t appear to be that prevalent.
But if by “aliens” we mean intelligent life with symbolic thought, then I’m with R Cawkwell. As far as we can tell, that kind of intelligence only evolved once on Earth, and our species very nearly didn’t make it, so it seems far from evolutionarily inevitable. The nearest alien civilization is probably very far away: think other galaxies, or maybe even other galactic superclusters, hundreds of millions of light years away, possibly billions, far enough that they haven’t had a chance to reach us yet.
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Setting aside the little teaser at the end of this post, this is about finding a planet with a biosphere of any kind, including a biosphere of only microorganisms. I’d like to think we’d find something like that relatively close by, but even that is not really what the paper I cited was promising.
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You might enjoy this page on Atomic Rockets. Do a find on ‘Fermi Paradox’
http://www.projectrho.com/public_html/rocket/aliencontact.php
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Thanks for the link! That was an interesting read. I did a post on the Fermi Paradox myself a while back. It’s kind of interesting how it started. Apparently Enrico Fermi saw a cartoon about Martians in the New Yorker, which then led to a long conversation with his colleagues, which then led to the concept we now have.
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Earth like planets? How about earth like moons.
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Those would be cool too! I heard we may have discovered our first exomoon too. And if we can start studying exomoons, that will really increase the odds of finding alien life.
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The biggest exomoon is about the size of Neptune and might support alien life, if it were a moon, not an exomoon, it would wouldn’t be worst than Europa , like way better. It would be my second favorite moon (But because it’s an exomoon it’s the best exomoon.
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Yeah, I’m very excited about that Neptune-sized exomoon. If its discovery is confirmed, it’ll challenge a lot of our assumptions about what moons can be like.
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I foresee a time when we’re analyzing the composition of an exo-atmosphere… plus or minus 20%… and argueing over whether the O2 means life exists there. It’ss be cool but not as amazing as everyone wishes for
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One of the interesting things I picked up from this paper was that we really can’t go looking for just one thing, like oxygen. We have to look at the whole planetary context, and it’ll probably take a long time to amass enough data on any one planet to do that.
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If it were possible to live on earth like planets…. One would have the radiation problem to overcome. Now provided we don’t kill ourselves from space sickness, our Next goal is to avoid thickening the atmosphere of the said planet …which means terraforming….which means change… which means lots of problems…… like staying alive and if unfortunately, a tank bursts, batteries burn out or oxygen runs out …… Space doesn’t seem so inviting anymore. Lets pray the aliens find us! I’m a believer, I AM! I believe Aliens will find Earth, its just a question of time.
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I guess we’ll see what happens. I for one think we’ll find alien life of some kind in the near future. Whether or not it will be intelligent life that we can communicate with… I’m more skeptical about that. But we’ll see!
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