Icy Enceladus also has a warm polar spot


POSTED: Saturday, June 20, 2009

In July 2005 the Cassini space probe, in orbit around Saturn, began sending back high-resolution images. One of the items of intense interest is Saturn's tiny moon, Enceladus.

During a fly-by last October, Cassini passed within 16 miles of the surface of this puzzling icy moon which is only 310 miles in diameter, barely one-tenth the size of our moon. It captured stunningly detailed images of its textured surface.

Cassini scientists have identified plumes of ice particles, water vapor and trace organic compounds emanating from the surface of Enceladus in at least eight locations in the moon's south polar region in the area called the tiger stripe fractures.

Unlike most bodies in the solar system, Enceladus exhibits a bizarre mixture of softened craters and complex, fractured terrains. An absence of craters on solid bodies indicates geological activity. On Earth plate tectonics and erosion have combined to erase most of the evidence of impacts, while our own geologically dead moon shows the full face of the impacts with its cratered surface. Cassini scientists expected the south pole of Enceladus to be cold because its bright icy surface reflects 80 percent of the sunlight that hits it. They found a dramatic warm spot centered on the pole.

Equatorial temperatures are around -315 degrees Fahrenheit, but the south pole's warm region reaches -305 F, with some spots reaching -261 F.

It seems likely that heat escaping from the interior of Enceladus warms the polar region and causes the plumes. This would make it only the third solid body in the solar system, after Earth and Jupiter's volcanic moon Io, where there are hot spots powered by internal heat.

The plume of gas emanating from the south polar region is 91 percent water, 4 percent nitrogen, 3.2 percent carbon dioxide and 1.6 percent methane, with trace amounts of other organic chemicals. The gases are similar to volcanic gases on Earth, and the composition of comets, although Enceladus is outwardly nothing like a comet.

Nonbiological processes produce a variety of organic compounds, and they are found throughout the solar system, but detecting a new source always arouses interest and encouragement to those who study the potential for extraterrestrial life.

Even if the conditions were not right for life to arise on Enceladus, life has been present on Earth for nearly 4 billion years, and in that time it has been bombarded with countless

meteor impacts. The largest of these were capable of ejecting material from Earth into space.  Some of these fragments could have escaped Earth's gravitation and may have contained bacteria and spores that could lie dormant in space, shielded from solar radiation and cosmic rays. If any of these fragments were to impact a planetary body such as Enceladus, it could “;seed”; this world.

Richard Brill is a professor of science at Honolulu Community College. E-mail questions and comments to .(JavaScript must be enabled to view this email address).