Tuesday, August 03, 2010

Best chance for life beyond Earth # 2: Enceladus

After Mars, Saturn and its several moons is the nearest best chance for finding life beyond Earth. In addition to the possibility of life the Saturn system possesses the best chance for finding natural resources such as methane and water.

The next large moon is Enceladus, measuring 504 km across, and orbiting at 238,000 km from the center of Saturn. NASA's Cassini spacecraft recently discovered geysers of water ice pouring out of Enceladus' southern pole. Astronomers think that there could be vast reserves of liquid water underneath the moon's icy surface.

Enceladus has the highest albedo (>0.9) of any body in the solar system. Its surface is dominated by fresh, clean ice.

At least five different types of terrain have been identified on Enceladus. In addition to craters there are smooth plains and extensive linear cracks and ridges. At least some of the surface is relatively young, probably less than 100 million years.

This means that Enceladus must have been active until very recently (and perhaps is still active today). Perhaps some sort of "water volcanism" is at work.

Enceladus is much too small to be heated solely by the decay of radioactive material in its interior at present. But briefly after its formation 4.5 billion years ago short-lived radioisotopes may have provided enough heat to melt and differentiate the interior. That combined with modest present day heating from long-lived isotopes and tidal heating may account for the present day activity on Enceladus.

Cassini closeup view (looks like Europa?) Enceladus is locked in a 1:2 resonance with Dione (similar to the situation between Io and Europa). This may provide a heating mechanism but it is probably insufficient to melt water ice. Enceladus may therefore be composed of some low-melting point material rather than pure water.

Enceladus is very likely the source of the material in Saturn's tenuous E ring. And since the material cannot persist in the ring for more than a few thousand years, it must be due to very recent activity on Enceladus. A less likely possibility is that the rings are maintained by high-velocity collisions between dust particles and the various moons.

Source: http://apod.nasa.gov/apod/ap060608.html