astrobiology

Astrobiology (or exobiology) is the study of life off of Earth. None has been found so it is speculative. The study includes:

• Modeling and search for signs of life such as compounds rare in nature but plentiful on Earth because of life.
• Modeling the conditions that would support the development and continuation of life such as habitable zones.
• Searches for signs of current or past life in planetary visits such as on Mars.

Reasoning out the conditions that might support life is of interest as is the reasoning out the possible signs of life, i.e., biosignatures. Life is thought to be most likely on a planet or moon when carbon is present, which is the element most likely to be the basis of very large, complex molecules, and when liquid water, a very effective solvent, is present, more likely with both.