Searching for Life in the Solar System

Timothy D. Swindle, Professor and Head, Planetary Sciences/Lunar and Planetary Laboratory When Renaissance scholars figured out that the planets are, like Earth, orbiting the Sun, an immediate assumption was that they are inhabited worlds. In the last 50 years, spacecraft have determined that life on the surfaces of planets and moons in the Solar System is rare – if it exists at all. However, there are places where a search for life in the Solar System may still be fruitful. Although the current surface of Mars is a hostile environment, early Mars may have been much more clement to life. Jupiter's moon Europa is almost certainly barren on the surface, but has an 'ocean' of liquid water underneath a crust of ice, where some terrestrial organisms might be able to thrive. Finally, Saturn's moon Titan would not be suitable for life from Earth, but has rain and seas of liquid hydrocarbons, raising questions about whether life needs liquid water, or just needs some abundant liquid.