The possibility of life on Mars and other planets is discussed, with the idea that life may have started on Mars and seeded Earth, as Mars was habitable before Earth for the type of chemistry that life on Earth is based on.
The Fermi paradox raises the question of why we haven't detected any signs of extraterrestrial life when the universe seems like it should be full of it, but this may be due to the assumptions we're making about the nature of that life. If we think statistically and look for life beyond our biology, we may find that the universe is full of it.