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"Curiosity - ha spiegato Elachi oggi - non è dotato di strumenti per trovare tracce biologiche", ossia molecole necessarie o prodotte da forme di vita, "ma ha l

"Curiosity - ha spiegato Elachi oggi - non è dotato di strumenti per trovare tracce biologiche", ossia molecole necessarie o prodotte da forme di vita, "ma ha la capacità di riconoscere molecole organiche". Già questa sarebbe una novità importante: tali molecole, composti a base di carbonio, non provano di per sé la presenza di vita, ma senza di loro la vita non può svilupparsi.

InclinedPlane 14y ago
What they're talking about is the difference between measuring a dead organism (looking at organic molecules, something Curiosity is capable of doing) on the one hand and performing experiments to detect active biological activity of a live organism on the other hand. Look at the experiments that the Viking Landers carried for examples of this: http://en.wikipedia.org/wiki/Viking_biological_experiments http://en.wikipedia.org/wiki/Viking_biological_experiments
gus_massa 14y ago
If Curiosity founds "formic acid", that is a simple 5 atom molecule, then it is not a proof of life, because there are some non-byological process that create that molecule, so it is distributed everywhere in the universe. (I'm not sure that "formic acid" is the best example, but probably any small organic molecule is a good enough example.) If Curiosity founds "celulose", that is a very complex ~20000 atom molecules, with the atoms arranged in a very special scheme, then it is almost almost almost sure that it was created by some kind of life, because we don't know any non-biological process that can make it. The main problem is that there is no distinction between organic and biological molecules, so you can't make a sensor that distinguishes them. The very simple molecules (formic acid) are expected to be found even in places without life. The intermediate molecules (some sugars, aminoacids, even some nucleotides) are more rare, but not unexpected. The big complex molecules are unexpected, so after discarding everything else, the conclusion would be that in that place there is something living. A similar problem is "How many grains of rice is a lot of rice?": One is not enough, one million is enough, but there is no a clear border. There is not a clear border between organic and biological molecules; the question is "Is the probability that a molecule like this was created by a life form greater than the probability that a molecule like this was created by an inorganic process?"
- Daniel_Newby 14y ago
  > The main problem is that there is no distinction between organic and biological molecules, so you can't make a sensor that distinguishes them. For a given molecule, life tends to strongly prefer either the left-handed or right-handed version. Curiosity's gas chromatograph can tell them apart. If it finds a strong handedness preference for several chemicals, then Mars almost certainly has life.
  - jacquesm 14y ago
    I think you may be confusing liquid chromatography and gas chromatography, gas chromatography afaik can't distinguish between the left handed and the right handed form of a molecule but liquid chromatography mass spectrometry can (and that's not the most sensitive / efficient way to do it either). http://en.wikipedia.org/wiki/Chirality http://en.wikipedia.org/wiki/Chirality
    - Daniel_Newby 14y ago
      One of the GC columns has a chiral stationary phase. Chromotography works whether the carrier fluid is a liquid or a gas. The real problem with gas chromotography is that amino acids have a low vapor pressure. They seem to be chemically functionalizing them to improve the volatility. http://msl-scicorner.jpl.nasa.gov/Instruments/SAM/ http://msl-scicorner.jpl.nasa.gov/Instruments/SAM/

InclinedPlane 14y ago

What they're talking about is the difference between measuring a dead organism (looking at organic molecules, something Curiosity is capable of doing) on the one hand and performing experiments to detect active biological activity of a live organism on the other hand. Look at the experiments that the Viking Landers carried for examples of this: http://en.wikipedia.org/wiki/Viking_biological_experiments http://en.wikipedia.org/wiki/Viking_biological_experiments

gus_massa 14y ago

If Curiosity founds "formic acid", that is a simple 5 atom molecule, then it is not a proof of life, because there are some non-byological process that create that molecule, so it is distributed everywhere in the universe. (I'm not sure that "formic acid" is the best example, but probably any small organic molecule is a good enough example.) If Curiosity founds "celulose", that is a very complex ~20000 atom molecules, with the atoms arranged in a very special scheme, then it is almost almost almost sure that it was created by some kind of life, because we don't know any non-biological process that can make it. The main problem is that there is no distinction between organic and biological molecules, so you can't make a sensor that distinguishes them. The very simple molecules (formic acid) are expected to be found even in places without life. The intermediate molecules (some sugars, aminoacids, even some nucleotides) are more rare, but not unexpected. The big complex molecules are unexpected, so after discarding everything else, the conclusion would be that in that place there is something living. A similar problem is "How many grains of rice is a lot of rice?": One is not enough, one million is enough, but there is no a clear border. There is not a clear border between organic and biological molecules; the question is "Is the probability that a molecule like this was created by a life form greater than the probability that a molecule like this was created by an inorganic process?"

Daniel_Newby 14y ago
> The main problem is that there is no distinction between organic and biological molecules, so you can't make a sensor that distinguishes them. For a given molecule, life tends to strongly prefer either the left-handed or right-handed version. Curiosity's gas chromatograph can tell them apart. If it finds a strong handedness preference for several chemicals, then Mars almost certainly has life.
- jacquesm 14y ago
  I think you may be confusing liquid chromatography and gas chromatography, gas chromatography afaik can't distinguish between the left handed and the right handed form of a molecule but liquid chromatography mass spectrometry can (and that's not the most sensitive / efficient way to do it either). http://en.wikipedia.org/wiki/Chirality http://en.wikipedia.org/wiki/Chirality
  - Daniel_Newby 14y ago
    One of the GC columns has a chiral stationary phase. Chromotography works whether the carrier fluid is a liquid or a gas. The real problem with gas chromotography is that amino acids have a low vapor pressure. They seem to be chemically functionalizing them to improve the volatility. http://msl-scicorner.jpl.nasa.gov/Instruments/SAM/ http://msl-scicorner.jpl.nasa.gov/Instruments/SAM/