We have no direct evidence (yet) that there is life on other planets, moons, or in interstellar space. Nevertheless, there are some compelling reasons to believe that eventually we will discover some, perhaps even in our own solar system. Here are seven reasons why scientists believe that life is out there, just waiting to meet us. It might not be green-skinned ladies in silver saucers, but it will be alien.
1. Extremophiles on Earth
One of the big questions is whether life could evolve and survive on a world radically different than Earth. The answer appears to be yes, if you consider that even Earth harbors extremophiles, or organisms that can survive in extremes of heat, cold, poisonous (to us) chemicals, and even in vacuum. We've found creatures who live without oxygen around the edges of super-heated volcanic vents at the bottom of the ocean, and we've found life in the brackish pools of the high Andes, as well as the ice-covered lakes of the arctic. There are even tiny creatures called tardigrades that can survive in the vacuum of space. So we have direct evidence that life can thrive in pockets of alien atmosphere on Earth. In other words, we know life can survive in conditions we've seen on other planets and moons. We just haven't found it yet.