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I make no assumptions to the nature of this planet. There are high chances it does not have an atmosphere or a lithosphere. But in a planet that shows a high level of radioactive activity, would it be advisable to probe for life, or is it improbable? Either way, why? How would we go about detecting life in such planets?

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  • $\begingroup$ What is the distribution of these radioactive zones and their concentrations? Earth for instance harbours ample of illegal substances beneath its crusts, and life still flourish as if they are being intoxicated. We also received cosmic rays and there's even a dude who turns himself into a temperamental green walking fly swapper who enjoys sending unaware victims soaring all over the sky or becomes a graffiti on the floor or wall. $\endgroup$ – user6760 Jun 12 '15 at 11:44
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At what level do you define life ? Bacterias, sentient, instinctive inteligence ?

https://en.wikipedia.org/wiki/Tardigrade

For example, they can withstand temperatures from just above absolute zero to well above the boiling point of water (100 °C), pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. They can go without food or water for more than 10 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.

Roaches are also known to be able to live in radiation but it does not fill the requirement to be without atmosphere.

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Earth-like life would be run into problems if enough energy is delivered through radiation, so that the organisms can't handle it. As bacteria are known to tap into unusual energy sources for earth-life, I think it should be thinkable that some alien life form can utilize the radiation as energy source for life (as plants utilize the sunlight). There might be still another limit: if radiation start to destroy the structural integrity of the molecules too fast for repairing, this would be deadly for every life-form.

Generally spoken simple life-form can withstand higher radiation-doses than humans, because of simpler genetic information, so we could expect more simple life forms in high radiation.

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  • $\begingroup$ I could imagine bacteria with two or even three copies of the DNA, so that when it replicates, it will fold twice and have a 50% chance of not passing damaged DNA or fold three times and favor the ones which have at least 2 pieces the same (a sort of organic checksum). $\endgroup$ – Neil Jun 12 '15 at 12:07
  • $\begingroup$ @Neil: nature thinks as you. All higher living beings (humans for instance) have a redundant second copy of the DNA. That is not entirely an copy, as sexual reproduction uses this duplication to give us one copy from the mother and another from the father, but as these are for more than 99% the same it acts as redundant. That helps to alleviate the problems of big DNA, that leads to masses of errors (along other stuff like repairing damaged DNA). If this is done in bacteria with much simpler genetic information, it would already help a great deal. $\endgroup$ – Mnementh Jun 12 '15 at 12:12
  • $\begingroup$ Single-celled organisms don't generally require copies, but if high radiation were constant, then I think that this would be the only way. $\endgroup$ – Neil Jun 12 '15 at 12:41
  • $\begingroup$ Not the only way, but one method. Extended rapair method and splitting the genome into more shorter strains might also help. Maybe life forms could developed some sort of radiation shielding. I'm not sure though, how this would work. $\endgroup$ – Mnementh Jun 12 '15 at 12:55
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If we're talking about more advanced/complex life, I would think that a protective layer would be all that's really needed. The evolution of life is a fairly complex and uncertain subject. As one example, on earth it took some 2 billion years for the first plant to appear on land. It can be a very slow process it seems, as well as, at times, a very fast process.

If there was a planet with very high radiation, I think all it would take to protect the DNA for reproduction and have not overly-mutated offspring would be a refillable sack of water around the entire body - not too different than how we have skin and fat as protection. An outer skin of water around the entire body would protect from a lot of radiation. Water is pretty good at blocking radiation.

Now, whether such an evolutionary adaptation like that is likely, I have no idea but I see no reason why it wouldn't be possible. Certainly sea life would have a chance even in a high radiation environment.

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