Ganymede may have a hidden ocean

ADD JUPITER'S moon Ganymede, which is bigger than two of the solar system's nine planets, to the growing list of worlds with evidence of liquid water under the surface. A thick layer of melted, salty water somewhere beneath Ganymede's icy crust would be the best way to explain some of the magnetic readings taken by NASA's Galileo spacecraft during close approaches to Ganymede in May 2000 and earlier, according to one new report.

In addition, the types of minerals on parts of Ganymede's surface suggest that, in the past, salty water may have emerged from below or melted at the surface, according to a study of infrared reflectance measured by Galileo. Third, new Galileo images of Ganymede hint how the water or slushy ice may have surfaced through the fractured crust, reminiscent of linear features on Europa, a neighboring moon believed likely to have a deep ocean beneath its ice.

They include the most detailed photos ever taken of Ganymede and an animated virtual flyover of an area where a smooth, bright swath resembling parts of Europa cuts across older, more heavily cratered terrain. The new information about Ganymede is being presented at the fall meeting of the American Geophysical Union, in San Francisco. Ganymede is the biggest moon in the solar system and bigger than the planets Mercury and Pluto.

The magnetic clues to a possible saltwater layer at Ganymede are more complicated than earlier magnetic evidence of hidden oceans on two other moons of Jupiter, Europa and Callisto, said Margaret Kivelson, a planetary scientist at the University of California, Los Angeles, and principal investigator for Galileo's magnetometer instrument. That's because Ganymede has a strong magnetic field of its own, instead of just a secondary field induced by Jupiter's magnetism.

A melted layer several kilometers or miles thick, beginning within 200 kilometers (120 miles) of Ganymede's surface would fit the data if it were about as salty as Earth's oceans, Kivelson said. Ganymede is covered with lots of ice and frost, both in the older, dark terrains and younger, bright terrains, said Thomas McCord, a geophysicist at the University of Hawaii.

Portions of Ganymede appear to have types of salt minerals that would have been left behind by exposure of salty water near or on the surface.

Send this article to Friends by E-Mail

Section  : Science & Tech
Next     : Boost for big bang theory