Saturn Moon May Feed Its Ring

By Sue Vorenberg SVORENBERG@ABQTRIB.COM / 823-3678

You can’t go skiing on the most snowy, icy body in the solar system. But you can look at the geysers that make Enceladus a significant, and sometimes surprising, moon.

Robert Tokar, a scientist at Los Alamos National Laboratory, and several co-authors released a paper Thursday about the moon and its geysers in the journal Science. Orbiting Saturn, Enceladus is geologically active, Tokar said, “which is a big deal” because it influences everything around it.

Geysers in Enceladus’ southern hemisphere cause snow to fall on the moon and affect the space around Enceladus, including Saturn’s rings and magnetic field.

The National Aeronautics and Space Administration’s Cassini spacecraft, which is orbiting Saturn, took images and collected other data from the moon and its geysers in July. The images are available on NASA’s Web site for anyone to see.

It looks like the geysers are feeding Saturn’s E-ring, the largest but least visible of the planet’s rings.

“This stuff (from the geysers) is bleeding off Enceladus and populating the whole area with water,” Tokar said.

That water over time has spread across the E-ring, which is nearly 200,000 miles wide. The ring is thickest near Enceladus, which strengthens the argument that the moon is feeding the ring, Tokar said.

“It really tells us about how the space around a planet — in this case, Saturn — fills up with water . . . (and) how volatile water can leave a planet and go elsewhere,” Tokar said.

Scientists have been studying the data from the July flyby for the past several months.

Los Alamos is involved in the project because it designed a key instrument on the Cassini spacecraft that detected water plasma — a special sort of gas — flowing off the moon during the flyby, Tokar said.

Nobody understands why the geysers appear only in the southern hemisphere, said Robert Johnson, an engineering physics professor at the University of Virginia, who also worked on the study.

“When they (NASA) flew by this moon, they found that there were jets of water molecules, which also contain some nitrogen and carbon dioxide and little grains, shooting out of its southern polar region,” Johnson said.

“That’s weird.” The jets might be coming from a liquid water body under the moon’s surface, although scientists still don’t know how deep that water body is, Johnson said. Johnson is working on a computer model of the geysers and how they function.

The geysers might have formed at the moon’s equator, because it is not symmetrical, which would cause geologic pressure and perhaps create a water body under the surface. Over time, Enceladus might have tipped due to the complex gravitational pull of Saturn and its other moons, pushing the geysers

to the south, Johnson said. Water from the geysers affects other parts of Saturn’s system besides the rings. Some of it falls back onto Enceladus as snow, which has kept the surface mostly free of visible craters, Tokar said. That water also turns into a plasma in the space around the planet, which feeds into Saturn’s magnetosphere, said Tom Hill, a physics and astronomy professor at Rice University who also participated in the study. Hill is creating a computer model of Enceladus’ magnetic field. “Plasma produces electric currents which inflate that magnetic field — blow it up like a balloon,” Hill said. “It (the field) moves back and forth radially towards and away from Saturn.” So far, the scientists have learned how much material is flowing out of the moon. While it sounds like the moon might eventually bleed away into nothing, that probably won’t happen for a long time — perhaps not until our solar system burns out 4.5 billion years from now, Hill said.