Oceans Might Be Common and Diverse

Oceans might be common and diverse in our solar system and in other solar systems, according to David Stevenson of Caltech, who regards the old notion of a narrow "habitable zone" (Venus too hot, Mars too cold, Earth just right) for liquid water oceans as erroneous.

Stevenson spoke earlier this week in San Francisco at a meeting of the American Geophysical Union at a session intended to bring together two scientific communities that scrutinize very different realms--the planets and the seafloor on Earth.

The connection? Observations from the bottom of the ocean show that microbes thrive both in near-freezing seawater and in near-boiling effusions from thermal vents. These conditions might turn up in many other planetary environments.

For example, the Galileo spacecraft has provided evidence for watery oceans on three of Jupiter's moons-Callisto, Ganymede, and Europa. Subsurface oceans could be kept liquid by warmth from tidal forces (Jove wringing its satellites) or from radioactivity. Torrance Johnson of JPL, also speaking that the meeting, said that Europa's ocean might be 75-150 km thick and could thus harbor twice the water in Earth's oceans.

Stevenson added that observations also hint at oceans on Titan, Triton, and Pluto. In the case of Titan (soon to get the Galileo treatment when the Cassini spacecraft reaches Saturn in 2004) an ocean would be a mixture of water and ammonia (acting as antifreeze). Under some circumstances water might even be found inside Uranus and Neptune.