first of all I'm not sure if I should post this here or in the astronomy stack. I think biologist are more likely to answer my question. To make it short:

Why when looking for any sort of life on other planets, we keep looking for similar conditions we call "life friendly", like nice temperature, oxygen level, pressure etc...

Is there some rule in biology that says life can only exists under these conditions? Why nobody supposes that evolution did not have enough time yet on our planet to generate other living mechanisms, and that on other planets even if the conditions are not suitable for us, there might be something well evolved through time there. After all if we can conceive electric robots that can survive to radioactivity and to high pressures and temperatures, why nature shouldn't be able to?

  • $\begingroup$ this topic has been discussed several times in this forum. If you search for related questions you'll find them. $\endgroup$ – WYSIWYG Apr 1 '14 at 6:05
  • $\begingroup$ technically, early life on earth didn't even need our sun because it didnt use photosynthesis, but for meaningful life you need plate techtonics, mountains and large landmasses, or it's a waterworld. Anywhere which has volcanos and seas should be able to support life, even if the surface temperature is -100 or -220C $\endgroup$ – aliential Dec 1 '16 at 3:55
  • $\begingroup$ If you want to ask a specific question about transistor or metal based life forms, you should check out the chemistry forums. there is a post about silicone there. $\endgroup$ – aliential Dec 28 '16 at 14:26

We might imagine living things that are very different from what we know. There is no conceptual reason for limiting life in its relation to water for example. Moreover, the definition of what is alive is really unclear. We classified more or less arbitrarily objects we know on earth as being living or not living but this does not give any clear definition of what is life and therefore it would not allow an exobiologist to even know what he's looking for!

But if you had to seek in billion of planets/natural satellite a living creature somewhere where what planets would start looking at? Probably those that look alike yours because you already know that life is possible the kind of conditions these planets offer. I think the answer is as easy as that.

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