Life on earth survives in a wide range of environments and in general seems to require three things which are a source of nutrients, a source of energy, and liquid water. Mars once had conditions that may have been conducive to an origin of life, if life arose it might still survive in pockets of liquid water underground. The possibility of life on europa or other jovian moons: Billions of stars have at least moderate size habitable zones in which life bearing planets might exist, with the. Kepler mission scientists hope soon to find evidence of potentially habitable worlds. We do not know how common or rare earth-like planets may be, arguments can be made on both sides of the question and at present we lack the data to determine their validity. Seti the search for extraterrestrial intelligence generally refers to efforts to detect signals such as radio or laser communications coming from civilizations on other worlds.