3 ms·

It would not be surprising if ancient life did exist on Mars, since impacts would likely have sent life back and forth between Earth and Mars (and possibly Venu

by pfdietz 4mo ago

It would not be surprising if ancient life did exist on Mars, since impacts would likely have sent life back and forth between Earth and Mars (and possibly Venus). For the same reason, the existence of ancient life on Mars would not show that life is likely to arise on Earth-like worlds, since one could not conclude it was an independent event.

stackghost 4mo ago
>impacts would likely have sent life back and forth between Earth and Mars By what mechanism is an impact giving some debris on Mars enough delta-V to reach Earth, without obliterating Mars and also sterilizing the debris due to heat and plasma?
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- alex_duf 4mo ago
  It's surprising but it's a real thing: https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Martian_meteorite
- metalman 4mo ago
  chunks get blasted off essentialy whole and unmodified, as they are contained in bigger chunks that act asl launch shields, though will exerience truely massive acceleration and then renentry on earth and other bodies. The evidence for life on mars is based on carbon nodules in rock, and things like CO² and methane gas,and some other chemistry and mineralology. The main one are the carbon nodules, which are ubiquitous in many sedimentary rocks on earth, though in the samples that I have of earth rocks, there are very often macro fossils that are naked eye identifiable There are countless miles of cliff here where everything has a fossil, but complete specimins, and soft tissue fossils remain rare, here, so the chances of such a thing making it to earth from mars, schould it exist in the first place are almost zero, though the martian ice caps could concievably hold meteors with earth life fossils that are naked eye visible and identifiable.
- pfdietz 4mo ago
  > By what mechanism. Impact spallation. When the strong shock wave generated in rock by an impact hits a rock/atmosphere (or rock/vacuum) surface, it is reflected, producing strong tensile stress. This causes very large acceleration while not subjecting the spalled layer to extreme temperature or pressure. This is the same process that HESH (High Explosive Squash Head) antitank rounds use to defeat tank armor without penetration. The explosive squashes against the armor before detonating, launching a shock through it causing material to spall off the inner surface at high speed. The shock here is weaker than in the impact case, however.
  - red-iron-pine 4mo ago
    while that's possible, it's also likely to burn the hell out of anything in / on / around. any would-be hitchhikers would need to be able to survive extinction-ish level impacts on Mars, survive through the vacuum (e.g. months), and then survive atmospheric re-entry and landing. and then be able to survive in the new ecosystem
    - pfdietz 4mo ago
      Certainly a great deal of energy is released. However, on the time scale of an impact, heat doesn't diffuse in rock very far. Even on the time scale of reentry to an atmosphere heat doesn't diffuse far. It's common for a meteorite that has fallen to Earth, despite the surface having been melted and ablated, to have an inside that is still freezing cold.
      - stackghost 4mo ago
        Ah, this was the piece I was missing. I assumed the heat of impact and/or re-entry would sterilize just about anything that wasn't an engineered heat shield.
        pfdietz 4mo ago
        The concern in the impact is how much heat is produced in the material itself, by the shock wave. A shock wave is dissipative, producing entropy and heat as it propagates, but near the spalled surface it cancels itself out and the heating becomes small.
eleveriven 4mo ago
In some ways the more interesting question might become whether Martian life, if found, shares the same basic biochemistry as Earth life
- pfdietz 4mo ago
  That is the question, yes. But if lithopanspermia is a thing, we don't need to go to Mars to investigate that question: we can look for this variant biochemistry life right here on Earth. This sounds to me like a valuable and economical research effort.

by pfdietz 4mo ago

stackghost 4mo ago

>impacts would likely have sent life back and forth between Earth and Mars By what mechanism is an impact giving some debris on Mars enough delta-V to reach Earth, without obliterating Mars and also sterilizing the debris due to heat and plasma?

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alex_duf 4mo ago
It's surprising but it's a real thing: https://en.wikipedia.org/wiki/Martian_meteorite https://en.wikipedia.org/wiki/Martian_meteorite
metalman 4mo ago
chunks get blasted off essentialy whole and unmodified, as they are contained in bigger chunks that act asl launch shields, though will exerience truely massive acceleration and then renentry on earth and other bodies. The evidence for life on mars is based on carbon nodules in rock, and things like CO² and methane gas,and some other chemistry and mineralology. The main one are the carbon nodules, which are ubiquitous in many sedimentary rocks on earth, though in the samples that I have of earth rocks, there are very often macro fossils that are naked eye identifiable There are countless miles of cliff here where everything has a fossil, but complete specimins, and soft tissue fossils remain rare, here, so the chances of such a thing making it to earth from mars, schould it exist in the first place are almost zero, though the martian ice caps could concievably hold meteors with earth life fossils that are naked eye visible and identifiable.
pfdietz 4mo ago
> By what mechanism. Impact spallation. When the strong shock wave generated in rock by an impact hits a rock/atmosphere (or rock/vacuum) surface, it is reflected, producing strong tensile stress. This causes very large acceleration while not subjecting the spalled layer to extreme temperature or pressure. This is the same process that HESH (High Explosive Squash Head) antitank rounds use to defeat tank armor without penetration. The explosive squashes against the armor before detonating, launching a shock through it causing material to spall off the inner surface at high speed. The shock here is weaker than in the impact case, however.
- red-iron-pine 4mo ago
  while that's possible, it's also likely to burn the hell out of anything in / on / around. any would-be hitchhikers would need to be able to survive extinction-ish level impacts on Mars, survive through the vacuum (e.g. months), and then survive atmospheric re-entry and landing. and then be able to survive in the new ecosystem
  - pfdietz 4mo ago
    Certainly a great deal of energy is released. However, on the time scale of an impact, heat doesn't diffuse in rock very far. Even on the time scale of reentry to an atmosphere heat doesn't diffuse far. It's common for a meteorite that has fallen to Earth, despite the surface having been melted and ablated, to have an inside that is still freezing cold.
    - stackghost 4mo ago
      Ah, this was the piece I was missing. I assumed the heat of impact and/or re-entry would sterilize just about anything that wasn't an engineered heat shield.
      - pfdietz 4mo ago
        The concern in the impact is how much heat is produced in the material itself, by the shock wave. A shock wave is dissipative, producing entropy and heat as it propagates, but near the spalled surface it cancels itself out and the heating becomes small.

eleveriven 4mo ago

In some ways the more interesting question might become whether Martian life, if found, shares the same basic biochemistry as Earth life

pfdietz 4mo ago
That is the question, yes. But if lithopanspermia is a thing, we don't need to go to Mars to investigate that question: we can look for this variant biochemistry life right here on Earth. This sounds to me like a valuable and economical research effort.