Quote:
Originally Posted by xelasnave
Even on Mars ...we should look deeper under the surface...as that possibilty needs to be investigated and ruled out or in...
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This is a fair point. Mars cannot be conclusively ruled out. The failing of the Martian magnetic field, with the resultant loss of atmosphere, cooling and sterilisation of the surface would have been a slow process, potentially allowing millions of years for bacteria to evolve around it.
There are bacteria living inside rocks in the dry valleys of Antarctica. No need for sunlight or direct contact with the atmosphere.
Go deep enough and there may still be liquid water in those rocks.
It may be an increasingly remote longshot, but certainly cannot be ruled out at this stage.
The difference between this, and other candidates like Europa, is that we are reasonably certain that in the past, Mars did have a climate that could have sustained life.