After reading Loren Eiseley wondering about our ignorance of the origins of life, I too wondered. And I to despaired over our ignorance! We've got merely ONE example of life here on Earth. We haven't even gotten the chance to explore mars with human eyes and hands and knees. I think the results are that mars had some active geology, surface water for some 100s of millions of years? It seems that life had a window of only a few 100million years on Earth to appear. So the question is: is life a natural consequence of chemistry or is it special? If Mars had conditions conducive to some kind of far from equilibrium chemistry developing for a couple 100 million years, and we explored for 100 years and found NO clues of mircrobial life then that would tell us something. If we DID find microbial fossils, that would tell us something again!
Of course of Venus, we are totally ignorant. Presumably Venus has had a much longer history of geological and chemical activity than mars. Our total igorance of details waiting in the rocks of Venus is a severe flaw in our attempt to fathom the origins of life.
As an aside, why isn't there massive amounts of funding for this exploration? Perhaps the powers that be are not to keen on busting through that question? Perhaps they are afraid to break the last barrier of belief that life is the special creation of God? That belief propelled by the same greed for eternal life that propels the funding for research in medicine?
And Titan? Io? Here are more places to look. So the verdict is in, Titan has methane rainfall. That means there are far from equilibrium cycles of methane evaporation and fall. It's cold there, but there is still 1/64th the amount of sunlight available as there is on Earth. Sunlight of the same quality as on Earth, so photochemistry CAN happen there. Just at 1/64 the rate it happens here. So instead of 4billion years of evolution, it's like 70million years... hm... What can happen in that amount of time? And Io and her sulfur volcanoes? What fascinating chemistry there is to explore! We've only just begun!