Principal Investigator Sara Seager
Biosignatures are signs of life in an exoplanet atmosphere or on an exoplanet surface. Earth’s biosignatures are oxygen (produced only in large quantities by plants and photosynthetic bacteria) and ozone (photochemically produced in the atmosphere from oxygen). Nitrous oxide is an atmospheric gas also produced by life, but is difficult to detect. Methane is produced both biologically and from mid-ocean ridge volcanism. Water vapor is considered a sign of habitability, because all life on Earth needs liquid water; atmospheric water vapor is indicative of liquid water oceans for terrestrial-like planets.
Earth twins refer to planets just like Earth, orbiting sun-like stars with liquid water oceans, continents, and thin atmospheres.