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> More likely, in all seriousness, that life originated in Mars and came here via panspermia during the early bombardment period. I am always surprised at the

by dpark 7y ago

> More likely, in all seriousness, that life originated in Mars and came here via panspermia during the early bombardment period. I am always surprised at the number of people willing to make assertions like this. Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely. > only relatively mature examples of Martian life (e.g. bacteria) would have survived the trip. Why do you make this assumption? Life complexity is not generally correlated with space survivability. At least not positively correlated.

partialrecall 7y ago
> "Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely." Perhaps not 'likely', but there is reason to believe it's plausible. Extremophile organisms plausibly capable of surviving in space for the requisite timespans are certainly known to exist, and there is also known to be small amounts of material transfer between earth and mars. The part I wonder about is whether any extremophile organism could survive the doubtlessly violent circumstances that are involved in ejecting rocks from either the earth or mars gravity well.
garmaine 7y ago
I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example of fossilized Martian life, analysis of the thermal stresses it suffered from ejection from Mars, time in flight, to impact on Earth showed conclusively that it was survivable. Had it been the other way around (Earth to Mars) it would have seeded Mars with life. We’ve shown that rock which could be carrying microbes can and has been exchanged between earth and Mars. Lots of such specimens land each and every year. You can quibble that we haven’t found actual life yet, but (1) lots of people think that’s exactly what ALH-84001 was. (2) we don’t have that many samples of Martian meteorites. We know lots of it falls every year, but most is either not found/collected/identified or contaminated on impact. (3) Mars meteorites falling now, ejected from a dry and sterile surface, would not be representative of what was falling in the early earth that was thrown from a wet, habitable Mars. To be clear, from an astrobiology perspective a negative result from the search for life on (or from) Mars is harder to explain than finding it. Both panspermia and second abiogenesis are simpler explanations.
- whatshisface 7y ago
  If bacteria have been riding meteorites to Mars for millions of years, why worry so much about sterilizing rovers?
  - linuxftw 7y ago
    I think finding life on Mars, even if you could prove it came from Earth through a natural process, would be significant. If you don't sterilize the rovers, then you can't trust the life is there naturally, and was perhaps introduced by us instead.
perl4ever 7y ago
"Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch." I think "from Mars specifically" is something that requires evidence to treat as likely. However, I don't think "Earth is the unique place where life originated" should be the default assumption according to Occam's razor. Nothing nearby is anything like Earth on the surface, but it's not speculation that there were billions of years and unimaginably large amounts of volume for life to develop underground in the rest of the universe, where it's warm and sheltered from radiation. The idea that nothing happened until Earth became "Earth-like" isn't the logical default. Naming the contrary of this far-fetched claim "panspermia" doesn't make it a "thing" that needs a "basis". By analogy, I would say that a creationist claim of humanity originating with Adam and Eve is what needs evidence, not the contrary assumption, that all humans had parents.
- garmaine 7y ago
  Where else? Venus' habitable period, if it existed, was quite short. It's gravity is also much higher and it is inward in the solar system. Even before it turned into the hell-hole it is now, dynamical models show that it probably sent few rocks our way. The Moon appears to have formed without the resources to sustain life as we know it. There are great candidates for life in the outer solar system (Europa, Enceladus, Titan), but ejecta from these mostly get eaten up by the giant planets. The only likely candidates for solar system origin panspermia is Mars, and maybe Ceres. Only Mars (and Earth) had the long wet period with open oceans, geothermal heat sources, plate tectonics, and sizable atmosphere. Mars isn't the only option, but the odds are way, way higher. At least for life as we know it. But the point of panspermia is that it would be life as we know it ;)
- ajmurmann 7y ago
  It seems that we don't know how likely life is to develop given early Earth conditions. If that has a very low chance to happen then maybe panspermia is more likely. If it turns out to likely happen given a few million years and good conditions maybe panspermia is less likely. It seems to me we know almost nothing about the likelihood of either option, so it's hard to declare that one should be the default.

by dpark 7y ago

partialrecall 7y ago

> "Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch. There is absolutely no basis for claiming that this is likely." Perhaps not 'likely', but there is reason to believe it's plausible. Extremophile organisms plausibly capable of surviving in space for the requisite timespans are certainly known to exist, and there is also known to be small amounts of material transfer between earth and mars. The part I wonder about is whether any extremophile organism could survive the doubtlessly violent circumstances that are involved in ejecting rocks from either the earth or mars gravity well.

garmaine 7y ago

I’ve actually worked in astrobiology research :) I would point you towards the research that went into ALH-84001. Even if you don’t buy that it was an example of fossilized Martian life, analysis of the thermal stresses it suffered from ejection from Mars, time in flight, to impact on Earth showed conclusively that it was survivable. Had it been the other way around (Earth to Mars) it would have seeded Mars with life. We’ve shown that rock which could be carrying microbes can and has been exchanged between earth and Mars. Lots of such specimens land each and every year. You can quibble that we haven’t found actual life yet, but (1) lots of people think that’s exactly what ALH-84001 was. (2) we don’t have that many samples of Martian meteorites. We know lots of it falls every year, but most is either not found/collected/identified or contaminated on impact. (3) Mars meteorites falling now, ejected from a dry and sterile surface, would not be representative of what was falling in the early earth that was thrown from a wet, habitable Mars. To be clear, from an astrobiology perspective a negative result from the search for life on (or from) Mars is harder to explain than finding it. Both panspermia and second abiogenesis are simpler explanations.

whatshisface 7y ago
If bacteria have been riding meteorites to Mars for millions of years, why worry so much about sterilizing rovers?
- linuxftw 7y ago
  I think finding life on Mars, even if you could prove it came from Earth through a natural process, would be significant. If you don't sterilize the rovers, then you can't trust the life is there naturally, and was perhaps introduced by us instead.

perl4ever 7y ago

"Panspermia itself is a hypothesis. Panspermia from Mars specifically is a huge stretch." I think "from Mars specifically" is something that requires evidence to treat as likely. However, I don't think "Earth is the unique place where life originated" should be the default assumption according to Occam's razor. Nothing nearby is anything like Earth on the surface, but it's not speculation that there were billions of years and unimaginably large amounts of volume for life to develop underground in the rest of the universe, where it's warm and sheltered from radiation. The idea that nothing happened until Earth became "Earth-like" isn't the logical default. Naming the contrary of this far-fetched claim "panspermia" doesn't make it a "thing" that needs a "basis". By analogy, I would say that a creationist claim of humanity originating with Adam and Eve is what needs evidence, not the contrary assumption, that all humans had parents.

garmaine 7y ago
Where else? Venus' habitable period, if it existed, was quite short. It's gravity is also much higher and it is inward in the solar system. Even before it turned into the hell-hole it is now, dynamical models show that it probably sent few rocks our way. The Moon appears to have formed without the resources to sustain life as we know it. There are great candidates for life in the outer solar system (Europa, Enceladus, Titan), but ejecta from these mostly get eaten up by the giant planets. The only likely candidates for solar system origin panspermia is Mars, and maybe Ceres. Only Mars (and Earth) had the long wet period with open oceans, geothermal heat sources, plate tectonics, and sizable atmosphere. Mars isn't the only option, but the odds are way, way higher. At least for life as we know it. But the point of panspermia is that it would be life as we know it ;)
ajmurmann 7y ago
It seems that we don't know how likely life is to develop given early Earth conditions. If that has a very low chance to happen then maybe panspermia is more likely. If it turns out to likely happen given a few million years and good conditions maybe panspermia is less likely. It seems to me we know almost nothing about the likelihood of either option, so it's hard to declare that one should be the default.