What are the conditions necessary for life on other planets?
When we ask about life in the universe, we have one point of reference: terrestrial life. Terrestrial life is entirely DNA based. But, when we search for life beyond Earth, we do not necessarily go looking for DNA-based life. We look for things that exhibit the common features of our life; that is, a self-organized, catalytic system capable of replication and evolution. Living systems require some discernible structure that maintains the integrity of the body plan while using energy and other materials from the environment to sustain it and to produce subsequent generations. One common indicator of life is that it changes its environment in ways that non-biological processes do not. In the search for life on other planets, scientists will look for disequilibria signatures, or chemicals in an environment that should not be there unless something biological was producing them.
