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I have just read What elements are a possible basis for life? and I find myself wondering whether instead of seeking advanced life-forms at remote locales a La SETI, and perhaps fundamentally differently, we ought to be looking for similar microscopic life forms on comets that pass off-and-on.

Granted, a comet may be near absolute 0 for a lot of the time, but microscopic life-forms are known to be capable of surviving lean periods by using a cyst, for instance. As far as the rest is concerned, comets probably contain some amount of ice, and hence water, too. Similarly a comet's sprint around the sun could provide some limited amount of gravity/mass too.

So, should we be looking for life on comets?

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Yes we should be and we are! Scientists have been analysing cometary material - but its a challenging task. The problem with looking at meteoritic material from comets on Earth is that it is generally contaminated with material from Earth. In addition, meteorites get physically altered during their passage through the Earth's atmosphere due to the high temperatures of re-entry.

So, the trick is to send missions to the comet. However, then the difficulty is in designing a mission that can analyse samples in situ. NASA's Stardust mission got around this by sample return to Earth. The probe visited comet Wild-2 and found the amino acid glycine among other interesting organic compounds. However, no evidence of life was found (metabolic products, organisms etc.) Further missions to comets (and asteroids) are planned, but they are not going to explicitly look for life.

Elsila, J.E., Glavin, D.P., & Dworkin, J.P. 2009, Meteoritics and Planetary Science, 44, 1323

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Changed inorganic to organic, i assume that is what you meant. I apologise if it wasn't. –  terdon Oct 16 '12 at 11:46
    
thanks @terdon that is what I meant! mind you, they found some very interesting inorganic compounds too ... –  Poshpaws Oct 16 '12 at 12:59
    
I imagined so, that's why I asked about the edit :). –  terdon Oct 16 '12 at 13:07

This is a cool idea and definitely we have found a lot of the chemicals important to life are associated with comets which have a lot of water too.

Another issue besides the v. low temperatures on comets, when they warm up to the sun are not long lived so I wonder if the a shorter lifespan would be an issue when they are seen in the temperate zones of the solar system.

Still any cometary mission should try to do a biological survey when such things are more economical. Right now even high profile missions like the current Mars missions are not spending any time looking for bacteria as we know it, but rather for other indications that life unlike our own might be there. Its been very cautious going for xenobiologists so far.

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