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There have certainly been metioroids starting on Mars that made it to Earth without being sterilized[1]. Now, Earth does have a deeper gravity well which might

There have certainly been metioroids starting on Mars that made it to Earth without being sterilized[1]. Now, Earth does have a deeper gravity well which might make a difference but Earth microbes have had geological epochs to make the trip to Mars wheres you'd only expect a meteoroid to remain recognizable on Earth's surface for that long in comparison. So I figure that if contamination of Mars by Earth life was a problem it would have happened by the Paleozoic. [1]https://en.wikipedia.org/wiki/Allan_Hills_84001 https://en.wikipedia.org/wiki/Allan_Hills_84001

david_shaw 11y ago
That makes sense, but wouldn't it be reasonable to assume that there's a major difference between natural seeding of life on other planets via meteors, and humans bringing it over while trying to find natural life? Furthermore, what if life on Mars were fragile enough that Earthly microscopic organisms destroyed it?
- WalterBright 11y ago
  At some point we'll either have to either stop worrying about life on Mars being hidden under a rock somewhere or forever put a "humans keep out" sign on Mars.
  - trose 11y ago
    I'm kinda of this thought process as well. If there are hospitable conditions there and we haven't found microbes after a while, I think we should just start dumping tons of them over there. We need something to put some atmosphere there for us. Algae seems to be a really good bet.
    - WalterBright 11y ago
      And suppose we do find some biological slime there? Does that then make Mars off limits to all of humanity for all time?
      - deleted 11y ago
        [deleted]
      - bdamm 11y ago
        It's time for us to accept that we implicitly modify everything we touch. Prime directive needs to have some detectability metric by which we decide it's OK for us to go gangbusters. If the native martian amoebas cannot survive with us present then they lose the evolution race, sorry. Besides, if there are primitive life forms on Mars, it's quite presumptuous of us to assume we could so easily wipe them out.
        outworlder 11y ago
        While I agree with the general idea, I also hope that, if there are more advanced civilizations out there and they find us, that they don't consider us "native amoebas".
        bdamm 11y ago
        Me too, although our morality doesn't influence their choices unless we can communicate with them and/or realistically fight for our survival. Do you think there are races out there quietly observing our behavior and preparing their verdict? If so, I sure hope we are given awareness of membership in the law before the sentencing.
        WalterBright 11y ago
        I seriously doubt anything at all will be found living on Mars, and if there is, it'll be primitive slime. Mars becomes infinitely more interesting if it can become a host for terrestrial life.
      - hollerith 11y ago
        I always thought that the main reason for being careful about bringing microbes to Mars is so that it is easier to tell whether any microbes we find on Mars evolved there. I thought that being careful about bringing microbes to Mars will stop being important to most of the people who currently care about it after we determine where any microbes we find there evolved. Was I wrong about that?
    - semi-extrinsic 11y ago
      In that scenario you're saying that the Martian landscape itself is not worthy of preservation, while any microorganisms could be. Both amoeba and rocks have no claim to consciousness etc., so why is one worthy of preservation while the other is not?
      - coldtea 11y ago
        OP is not interested in preservation for preservation's sake. It's not like we should care about the consciousness of microbes. What he meant, as I read it, is that if there are microbes we'll want to sample them and study them BEFORE we change the landscape and possible kill them.
  - joesb 11y ago
    If there were life on Mars. It will be the our first, and may be the possible only, source of foreign life to study. I don't think we want to contaminate or destroy our only source of knowledge on other kind of life. May be we can do that later, once we study them enough or have kept it enough for further study. But let's not make our first decision be "We gonna destroy it someday anyway, let's just stomp on it carelessly right now"
- mtdewcmu 11y ago
  >> wouldn't it be reasonable to assume that there's a major difference between natural seeding of life on other planets via meteors, and humans bringing it over while trying to find natural life? There would definitely be a difference vis-a-vis reconstructing the natural history of Mars.
- dogma1138 11y ago
  I don't think the care as much about contamination in the way it might mess with the martian ecosystem, what they do care about is getting uncontaminated results. Finding a life outside of Earth will be one of the greatest discoveries of man kind, something that will never be overshadowed by anything. They want to make sure that when we'll find something it didn't catch a ride on what ever we sent to find it. Eventually when we start exploring space it wouldn't really matter, yes some precautions might still be kept but we wouldn't take as much care as we do now. I for one also do not see humans contaminating an alien ecosystem as something unnatural, humans evolved, they've spread out, they seed life (intentionally or otherwise) this is just as much of a natural process as the potential for comets and meteorites to seed solar systems and beyond with organic compounds and even life it self.
mrec 11y ago
Well, calling Allan Hills 84001 "unsterilized" is a bit of a stretch, since even the most optimistic theory is that it contains fossilized lifeforms, not live ones. I dunno. I agree that something like the K/T impactor probably blasted bits of our planet all over the Solar System, but I suspect the depth of the gravity well brings more factors into play than just "how long it would take for ejecta to get to X". For example, accelerating a bit of surface to escape velocity would involve a lot more energy on Earth than on Mars, and at the point of impact I'd have thought that energy would translate to possibly-sterilizing heat.
- Symmetry 11y ago
  The hypothesis, I believe, is that the stuff in Allan Hills 84001 was fossilized back when Mars was wet but it was only ejected a few million years ago. The important part is that the inside of the rock never got too hot. As long as there are bacteria which can take being frozen for long periods of time they ought to be able to survive. As to larger impacts I really can't speak with any authority and I'm not aware of any studies which would say. But my intuition would be that the greater volumes in large the ejecta from large impacts would heat up less due to more insulation. I should probably put this on /r/askScience and see if anybody knows more.
- Retric 11y ago
  Large asteroids are generally frozen on the inside when they impact the earth, similarly any large ejecta would likely contain pockets that remain relatively cool. Polar ice would actually be a great candidate for such a transit.

david_shaw 11y ago

That makes sense, but wouldn't it be reasonable to assume that there's a major difference between natural seeding of life on other planets via meteors, and humans bringing it over while trying to find natural life? Furthermore, what if life on Mars were fragile enough that Earthly microscopic organisms destroyed it?

WalterBright 11y ago
At some point we'll either have to either stop worrying about life on Mars being hidden under a rock somewhere or forever put a "humans keep out" sign on Mars.
- trose 11y ago
  I'm kinda of this thought process as well. If there are hospitable conditions there and we haven't found microbes after a while, I think we should just start dumping tons of them over there. We need something to put some atmosphere there for us. Algae seems to be a really good bet.
  - WalterBright 11y ago
    And suppose we do find some biological slime there? Does that then make Mars off limits to all of humanity for all time?
    - deleted 11y ago
      [deleted]
    - bdamm 11y ago
      It's time for us to accept that we implicitly modify everything we touch. Prime directive needs to have some detectability metric by which we decide it's OK for us to go gangbusters. If the native martian amoebas cannot survive with us present then they lose the evolution race, sorry. Besides, if there are primitive life forms on Mars, it's quite presumptuous of us to assume we could so easily wipe them out.
      - outworlder 11y ago
        While I agree with the general idea, I also hope that, if there are more advanced civilizations out there and they find us, that they don't consider us "native amoebas".
        bdamm 11y ago
        Me too, although our morality doesn't influence their choices unless we can communicate with them and/or realistically fight for our survival. Do you think there are races out there quietly observing our behavior and preparing their verdict? If so, I sure hope we are given awareness of membership in the law before the sentencing.
      - WalterBright 11y ago
        I seriously doubt anything at all will be found living on Mars, and if there is, it'll be primitive slime. Mars becomes infinitely more interesting if it can become a host for terrestrial life.
    - hollerith 11y ago
      I always thought that the main reason for being careful about bringing microbes to Mars is so that it is easier to tell whether any microbes we find on Mars evolved there. I thought that being careful about bringing microbes to Mars will stop being important to most of the people who currently care about it after we determine where any microbes we find there evolved. Was I wrong about that?
  - semi-extrinsic 11y ago
    In that scenario you're saying that the Martian landscape itself is not worthy of preservation, while any microorganisms could be. Both amoeba and rocks have no claim to consciousness etc., so why is one worthy of preservation while the other is not?
    - coldtea 11y ago
      OP is not interested in preservation for preservation's sake. It's not like we should care about the consciousness of microbes. What he meant, as I read it, is that if there are microbes we'll want to sample them and study them BEFORE we change the landscape and possible kill them.
- joesb 11y ago
  If there were life on Mars. It will be the our first, and may be the possible only, source of foreign life to study. I don't think we want to contaminate or destroy our only source of knowledge on other kind of life. May be we can do that later, once we study them enough or have kept it enough for further study. But let's not make our first decision be "We gonna destroy it someday anyway, let's just stomp on it carelessly right now"
mtdewcmu 11y ago
>> wouldn't it be reasonable to assume that there's a major difference between natural seeding of life on other planets via meteors, and humans bringing it over while trying to find natural life? There would definitely be a difference vis-a-vis reconstructing the natural history of Mars.
dogma1138 11y ago
I don't think the care as much about contamination in the way it might mess with the martian ecosystem, what they do care about is getting uncontaminated results. Finding a life outside of Earth will be one of the greatest discoveries of man kind, something that will never be overshadowed by anything. They want to make sure that when we'll find something it didn't catch a ride on what ever we sent to find it. Eventually when we start exploring space it wouldn't really matter, yes some precautions might still be kept but we wouldn't take as much care as we do now. I for one also do not see humans contaminating an alien ecosystem as something unnatural, humans evolved, they've spread out, they seed life (intentionally or otherwise) this is just as much of a natural process as the potential for comets and meteorites to seed solar systems and beyond with organic compounds and even life it self.

mrec 11y ago

Well, calling Allan Hills 84001 "unsterilized" is a bit of a stretch, since even the most optimistic theory is that it contains fossilized lifeforms, not live ones. I dunno. I agree that something like the K/T impactor probably blasted bits of our planet all over the Solar System, but I suspect the depth of the gravity well brings more factors into play than just "how long it would take for ejecta to get to X". For example, accelerating a bit of surface to escape velocity would involve a lot more energy on Earth than on Mars, and at the point of impact I'd have thought that energy would translate to possibly-sterilizing heat.

Symmetry 11y ago
The hypothesis, I believe, is that the stuff in Allan Hills 84001 was fossilized back when Mars was wet but it was only ejected a few million years ago. The important part is that the inside of the rock never got too hot. As long as there are bacteria which can take being frozen for long periods of time they ought to be able to survive. As to larger impacts I really can't speak with any authority and I'm not aware of any studies which would say. But my intuition would be that the greater volumes in large the ejecta from large impacts would heat up less due to more insulation. I should probably put this on /r/askScience and see if anybody knows more.
Retric 11y ago
Large asteroids are generally frozen on the inside when they impact the earth, similarly any large ejecta would likely contain pockets that remain relatively cool. Polar ice would actually be a great candidate for such a transit.