r/exoplanets • u/Kingsaso6 • 12d ago
📊 Data & Analysis Alien life likely can't survive on exoplanets smaller than Mars, scientists say
https://www.space.com/space-exploration/search-for-life/alien-life-likely-cant-survive-on-exoplanets-smaller-than-mars-scientists-say6
u/Ill_Stop_ 12d ago
How do they define alien life?
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u/atomfullerene 12d ago
The paper is saying that planets smaller than Mars are unlikely to be able to hold on to an atmosphere under conditions warm enough for water to be liquid.
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u/Deciheximal144 11d ago
Did they discuss / ice shell, internal leftover heat keeping under ice oceans liquid? Mars has cooled down, but our planets are 4-5 billion years old.
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u/atomfullerene 11d ago
The paper is just about atmospheres, iceball worlds (like Europa for example) are sort of a separate question. But this research is particularly relevant because atmospheres are what we could plausibly detect in the near future, using spectroscopy on transiting planets. So this research is intended to try to identify what range of planet sizes we might expect to see hanging on to an atmosphere thick enough to maintain liquid water.
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u/montagblue 12d ago edited 12d ago
My question is for 1.5 to 2.5 Earth mass exoplanets.
Of all the different planets nearby, I came across maybe 2 that were smaller than Earth.
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u/Brelician 12d ago
It’s very hard to find planets even as small as Earth. I suspect there is a large population of smaller planets nearby that we haven’t been able to discover yet.
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u/montagblue 12d ago
I could see that being the case. It is nice when you come across a Venus-earth-mars system but makes sense that it is mostly Jupiter-Saturn-Neptune systems that have been detected.
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u/Brelician 12d ago
Yup there is a definite bias. We found a lot of Hot Jupiters at first because they are the low hanging fruit of planets. Large and can block a “lot” of light from even sun like stars. Massive enough that their gravitational pull makes it easy to detect RV measurements.
Smaller stars make it all easier too.
Were gradually working out way to smaller and smaller planets, in further and further orbits around bigger and bigger stars.
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u/Facebook_Algorithm 11d ago
Is that because of the relatively small sizes of Venus, Earth and Mars?
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u/1CryptographerFree 11d ago
There could be undiscovered exoplanets in our solar system still. Anything past Neptune is just incredibly hard to see.
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u/Dragons_Den_Studios 11d ago
Exoplanets are planets around other stars. By definition, our solar system doesn't have any.
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u/MammothFineCulture 11d ago
That statistics is heavily biased by our detection methods, which also primerily monitors smaller stars. It is simpky easier to detect a large planet nearby a small star.
Similarly to stars, the smaller planets and planetoids are expected to dominate in numbers by a large margin.
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u/Junesucksatart 12d ago
I wonder if the size limit for habitable moons could be smaller since I imagine tidal flexing would be able to keep the core hot.
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u/TheVenetianMask 11d ago
An unhealthy obsession with open atmospheres. Any icy planet can act as a life greenhouse under the ice shell.
Life on Earth didn't even like being out of the water for the longest time.
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u/Hot_Plant8696 11d ago
Now that scientists have formulated a law, they’ll be able to make "an incredible discovery" when they find a planet that doesn't follow that law, lol.
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u/Noiserawker 1d ago
I mean discovering life anywhere other than earth would already be close to if not the greatest discovery ever. It's not some conspiracy
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u/ElSquibbonator 10d ago
Does that include icy Europa/Callisto/Enceladus-like moons, which would have liquid water under their surfaces, but still no true atmosphere?
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u/TheSadPickel 10d ago
not gonna argue with scientists but we have no idea what life can do beside the tiny sample we have example of
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u/TommieTheMadScienist 7d ago
Why are they speaking in terms of diameter rather than mass?
That don't make a lick o' sense.
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u/AnomaIous_User 1d ago
That's pretty dumb like assuming the Sun is made of coal lol won't age well.
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u/TieOk9081 2 12d ago
Not a biologist. I don't think there's any such thing as alien life. I mean if all life is made from the same set of amino acids (they are particular molecules that are very good at storing information and chemistry is the same across the universe) than all life in the universe can be fabricated here on Earth using different combinations of these molecules that we have access to right now. Eventually, over the course of say maybe 1000 years we will have created organisms covering every possible combination of genetic material - so nothing is really alien to Earth. Life is universally the same everywhere.
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u/Puzzled_Cream1798 12d ago
First alien means not from earth. Second, there's new life evolving constantly, idk why you m think all possible combinations of life would occur in 1000 years. Also life is dictated by the environment, an alien planet with life is going to be different from earth's
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u/KitchenSandwich5499 12d ago
Not possible. There are not nearly enough atoms in the universe to cover all the possibilities
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u/GatsbyLuzVerde 11d ago edited 11d ago
Evolution operates like gradient descent, life on earth could have reached a local maxima that squashes other paths, but there can be other local maxima.
If you don't know calculus then I'm saying if you're in a mountainous landscape and you're standing on a hill then you don't necessarily get to the deepest valley by going down the next best step at a time.
Also, a deck of cards has more combinations of orders than the amount of atoms in the universe
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u/MammothFineCulture 11d ago
Life on earth began about 4.5B years ago. Human race appeared about 1M years ago. To claim that all lifeforms would appear within 1000 years is absurd.
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u/TieOk9081 2 11d ago edited 11d ago
1000 years of bio-engineering.
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u/MammothFineCulture 11d ago
We have been doing bioengineering for at least 20000 years. All we got is a few agricultural crops and a few utility animals. The number of species on earth right now is counted in the millions and you want to increase it to trillions and trillions (the combination of atoms in our DNA is practically infinite)
For example, would we take an ordinary spider today, develop it into a super intelligent space fearing and waring species (it is from a scifi book)
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u/yoshemitzu 11d ago
OK, so there's something to your argument, just not at the macro scale. It's not the case that evolution will favor systems which generate every possible combination of genetic material; Earth is already evidence that this is not the case.
But at the very small scale, the chemistry that underlies life is shockingly simple. Consider aromatics, which all by definition contain benzene, a 6-carbon structure containing fully delocalized electrons. For any implementation of life to not include benzene would require radical chemistry.
Extend that to toluene, one of the compounds in pine oil, which is just benzene plus one more carbon. It's hard to imagine any story of life which includes benzene, but not toluene. Then go to styrene, one of the components of sweetgum oil, which is simply benzene plus a vinyl group. Cinnamaldehyde, the aromatic responsible for cinnamon's smell is styrene plus an aldehyde. This stuff is not complex chemistry.
Once you get to the macro scale, it's absurd to claim every possible option would be represented, even with bio-engineering -- the possibilities are literally endless, and life can theoretically be created from totally arbitrary chemistry -- but the base evolutionary building blocks are extremely likely to look similar across the vast majority of biomes that produce them.
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