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Unfortunately that is not the way the microbes of this world (and now other worlds) work. The form that is really tough is the bacterial spore (spores are one o

Unfortunately that is not the way the microbes of this world (and now other worlds) work. The form that is really tough is the bacterial spore (spores are one of the lifecycle stages of some bacteria). These spores can survive in a complete vaccuum for years. The more bacteria you introduce into a system the more spores you will end up with contaminating everything. I personally doubt that this contamination is much of a problem. The planets of the solar system have been dusted in earth rocks containing bacterial spores thrown up by large asteroid strikes for billions of years.

dom96 8y ago
It's certainly a problem when the spacecraft's job is to detect life on other planets. If the spacecraft is contaminated with Earth microbes then it will get a false positive which is a huge problem.
- credit_guy 8y ago
  There’s zero chance any scientist will mistake the DNA of an existing Earth microbe with alien life.
  - brilee 8y ago
    There's an open hypothesis that life may have evolved elsewhere in the universe and then brought to Earth by some means. DNA would probably have diverged by now, but who knows?
    - havemylife 8y ago
      As I understand it DNA and RNA store their information in the form of certain amino acids. If other life uses amino acids in a similar fashion they may not use the same ones that life on Earth uses. Life here uses I believe 20 different amino acids and there are several hundred known. So there's potential there I would imagine in regards to testing that hypothesis. However what mainly bothers me with it is that it doesn't explain the origin of life and why Earth couldn't have original life begin on it. Unless we can rule out that early Earth conditions would have been too inhospitable for life to start but was sufficient to sustain it I see no reason to think an extraterrestrial origin to Earth life is more likely.
      - brilee 8y ago
        Agreed that the extraterrestrial origin hypothesis doesn't actually explain anything. It just merely adds a factor to the Drake equation of how likely it is for life to get started.
      - a1369209993 8y ago
        > As I understand it DNA and RNA store their information in the form of certain amino acids. Actually, information is stored as RNA, with DNA as long-term storage (mnemonic: RAM nucleic acid vs disk nucleic acid) and then amino acids are assembled into proteins (hardware) based on that information. Proteins only function as information storage in pathological cases like prions. But yes, if 'alien' life used the same 20 amino acids, and especially if it has the same mapping from 64 nucleic acid triplets to 20 amino acids, then that's confirmation that it's actually just a earth microbe that escaped or was left behind.
    - learnstats2 8y ago
      You can identify statistical differences after some generations of bacterial life in the lab, as far as I recall, i.e. a very short period of time at human-scale. Therefore, yes, life would have diverged sufficiently that scientists should be able to tell the difference.
  - tgb 8y ago
    I don't think any search for life on other planets begins with looking for and sequencing DNA so the time between getting a false positive and disconfirming it could be a decade or more and be extremely costly to send unneeded equipment to Mars or Europa or wherever.
    - credit_guy 8y ago
      That's a very good point, I didn't think of this lag. Now considering we just did this thought experiment, maybe it wouldn't be a bad idea for any mission to Mars in search of life to have some cheap way of identifying Earth-based microbes, by, for example, coupling a cheap microscope with some machine learning. It wouldn't replace DNA sequencing, but it could be 95% there. Oh, and by the way, assuming we do find some extraterrestrial life form, wouldn't we want to find the way it encodes information as soon as possible, rather than wait for a decade or more for a follow up mission?
      - breck 8y ago
        Are there machines that can sift through a sample of dirt, detect cells and isolate them for library prep and sequencing? Or are you thinking of human missions to Mars?
        Firadeoclus 8y ago
        It seems likely that there will be such machines within a few years. There is nothing in this procedure which can't be automated using existing technology.
      - VLM 8y ago
        > identifying Earth-based microbes An extremely expensive although effective approach would be to "seed" the spacecraft with isotopically enriched and documented solvents and food sources such that all the oxygen or carbon or both on the spacecraft, if any contamination DOES exist, would be a peculiar and documented isotope ratio that is different than Mars ratios. I think we know the natural ratios for Mars in bulk material, so anything immediately found to be growing that matched the documented "salted" isotope ratios obviously was a spacecraft contaminant whereas anything mars ratio was local. Of course bacteria can reproduce fast, so Earth bacteria eating Mars material would rapidly revert to Mars isotope ratios. Still for the first hour on the ground this would likely be usable for life detection experiments. Although it would probably be unimaginably expensive.
  - gnulinux 8y ago
    > There's zero chance Why do you assume so? It's possible a sattelite in the Solar System was contaminated by Earthling bacterias via asteroids and somehow miracalously adapted that environment. If this is true, scientists would find a group of bacteria branched off of bacteria here on Earth a billion year ago or so.
- danieltillett 8y ago
  The reason I don't think it is a problem is that "Earth" microbes will have got to the planet long before the spacecraft.
  - colanderman 8y ago
    Uh, it kind of is a problem if that statement is the hypothesis the probe is designed to test.
    - danieltillett 8y ago
      Even if the probe was not contaminated the planets already are. We are likely to find that there is life on Mars (underground) and it looks just like life on Earth. One interesting theory is that life originated outside the Earth (say on Mars) and was transported to Earth at a later time. This theory would explain why LUCA [0] is so complex and why life appears almost as soon the Earth had liquid water [1]. 0. https://en.wikipedia.org/wiki/Last_universal_common_ancestor https://en.wikipedia.org/wiki/Last_universal_common_ancestor 1. https://en.wikipedia.org/wiki/Earliest_known_life_forms https://en.wikipedia.org/wiki/Earliest_known_life_forms
      - gruez 8y ago
        >This theory would explain why LUCA [0] is so complex and why life appears almost as soon the Earth had liquid water [1]. from the wikipedia article: >LUCA should not be assumed to be the first living organism on Earth
        danieltillett 8y ago
        On the other hand it should not be assume that it is not. The complexity of LUCA is a problem since LUCA is not much less complex than a modern bacteria which is very, very complex.
      - colanderman 8y ago
        Yes, but you can't test that hypothesis if the probe is contaminated. Science isn't about assuming likely things to be true.
ss2003 8y ago
Not to mention asteroids of interstellar origin.

dom96 8y ago

It's certainly a problem when the spacecraft's job is to detect life on other planets. If the spacecraft is contaminated with Earth microbes then it will get a false positive which is a huge problem.

credit_guy 8y ago
There’s zero chance any scientist will mistake the DNA of an existing Earth microbe with alien life.
- brilee 8y ago
  There's an open hypothesis that life may have evolved elsewhere in the universe and then brought to Earth by some means. DNA would probably have diverged by now, but who knows?
  - havemylife 8y ago
    As I understand it DNA and RNA store their information in the form of certain amino acids. If other life uses amino acids in a similar fashion they may not use the same ones that life on Earth uses. Life here uses I believe 20 different amino acids and there are several hundred known. So there's potential there I would imagine in regards to testing that hypothesis. However what mainly bothers me with it is that it doesn't explain the origin of life and why Earth couldn't have original life begin on it. Unless we can rule out that early Earth conditions would have been too inhospitable for life to start but was sufficient to sustain it I see no reason to think an extraterrestrial origin to Earth life is more likely.
    - brilee 8y ago
      Agreed that the extraterrestrial origin hypothesis doesn't actually explain anything. It just merely adds a factor to the Drake equation of how likely it is for life to get started.
    - a1369209993 8y ago
      > As I understand it DNA and RNA store their information in the form of certain amino acids. Actually, information is stored as RNA, with DNA as long-term storage (mnemonic: RAM nucleic acid vs disk nucleic acid) and then amino acids are assembled into proteins (hardware) based on that information. Proteins only function as information storage in pathological cases like prions. But yes, if 'alien' life used the same 20 amino acids, and especially if it has the same mapping from 64 nucleic acid triplets to 20 amino acids, then that's confirmation that it's actually just a earth microbe that escaped or was left behind.
  - learnstats2 8y ago
    You can identify statistical differences after some generations of bacterial life in the lab, as far as I recall, i.e. a very short period of time at human-scale. Therefore, yes, life would have diverged sufficiently that scientists should be able to tell the difference.
- tgb 8y ago
  I don't think any search for life on other planets begins with looking for and sequencing DNA so the time between getting a false positive and disconfirming it could be a decade or more and be extremely costly to send unneeded equipment to Mars or Europa or wherever.
  - credit_guy 8y ago
    That's a very good point, I didn't think of this lag. Now considering we just did this thought experiment, maybe it wouldn't be a bad idea for any mission to Mars in search of life to have some cheap way of identifying Earth-based microbes, by, for example, coupling a cheap microscope with some machine learning. It wouldn't replace DNA sequencing, but it could be 95% there. Oh, and by the way, assuming we do find some extraterrestrial life form, wouldn't we want to find the way it encodes information as soon as possible, rather than wait for a decade or more for a follow up mission?
    - breck 8y ago
      Are there machines that can sift through a sample of dirt, detect cells and isolate them for library prep and sequencing? Or are you thinking of human missions to Mars?
      - Firadeoclus 8y ago
        It seems likely that there will be such machines within a few years. There is nothing in this procedure which can't be automated using existing technology.
    - VLM 8y ago
      > identifying Earth-based microbes An extremely expensive although effective approach would be to "seed" the spacecraft with isotopically enriched and documented solvents and food sources such that all the oxygen or carbon or both on the spacecraft, if any contamination DOES exist, would be a peculiar and documented isotope ratio that is different than Mars ratios. I think we know the natural ratios for Mars in bulk material, so anything immediately found to be growing that matched the documented "salted" isotope ratios obviously was a spacecraft contaminant whereas anything mars ratio was local. Of course bacteria can reproduce fast, so Earth bacteria eating Mars material would rapidly revert to Mars isotope ratios. Still for the first hour on the ground this would likely be usable for life detection experiments. Although it would probably be unimaginably expensive.
- gnulinux 8y ago
  > There's zero chance Why do you assume so? It's possible a sattelite in the Solar System was contaminated by Earthling bacterias via asteroids and somehow miracalously adapted that environment. If this is true, scientists would find a group of bacteria branched off of bacteria here on Earth a billion year ago or so.
danieltillett 8y ago
The reason I don't think it is a problem is that "Earth" microbes will have got to the planet long before the spacecraft.
- colanderman 8y ago
  Uh, it kind of is a problem if that statement is the hypothesis the probe is designed to test.
  - danieltillett 8y ago
    Even if the probe was not contaminated the planets already are. We are likely to find that there is life on Mars (underground) and it looks just like life on Earth. One interesting theory is that life originated outside the Earth (say on Mars) and was transported to Earth at a later time. This theory would explain why LUCA [0] is so complex and why life appears almost as soon the Earth had liquid water [1]. 0. https://en.wikipedia.org/wiki/Last_universal_common_ancestor https://en.wikipedia.org/wiki/Last_universal_common_ancestor 1. https://en.wikipedia.org/wiki/Earliest_known_life_forms https://en.wikipedia.org/wiki/Earliest_known_life_forms
    - gruez 8y ago
      >This theory would explain why LUCA [0] is so complex and why life appears almost as soon the Earth had liquid water [1]. from the wikipedia article: >LUCA should not be assumed to be the first living organism on Earth
      - danieltillett 8y ago
        On the other hand it should not be assume that it is not. The complexity of LUCA is a problem since LUCA is not much less complex than a modern bacteria which is very, very complex.
    - colanderman 8y ago
      Yes, but you can't test that hypothesis if the probe is contaminated. Science isn't about assuming likely things to be true.

ss2003 8y ago

Not to mention asteroids of interstellar origin.