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Saturn Moon's Ice Geysers Create "Cosmic Graffiti"

Brian Handwerk
for National Geographic News
February 8, 2007
 
Saturn's moon Enceladus is spewing giant geysers of ice that have sandblasted several nearby moons, making them some of the solar system's most reflective objects, research shows.

A new study published in the journal Science bills Enceladus as "a cosmic graffiti artist, caught in the act."

Last spring NASA's Cassini spacecraft showed what appeared to be geysers streaming out from Enceladus's surface.

(Read related story: "Saturn Moon Has Water Geysers and, Just Maybe, Life" [March 10, 2006].)

One theory suggests that the plumes are created by liquid water below the surface that freezes instantly in the moon's frigid surface climate.

"Enceladus coats itself, snows on itself, and distributes pure water ice particles on its surface," said lead study author Anne Verbiscer, an astronomer at the University of Virginia.

The fluffy texture of this icy coating allows Enceladus to reflect more of the sun's light than any other body in the solar system.

And its neighbor moons are nearly as bright, thanks to the sprays of ice they receive from Enceladus, the researchers say.

"The message seems to be, the closer you are to Enceladus the brighter your surface will be, because it has been coated with fine ice particles from the Enceladus plumes," said Andrew Ingersoll, a planetary meteorologist at the California Institute of Technology, who was not an author of the new study.

"Of course, we still haven't figured out why Enceladus is so special."

Signs of Life?

Like many other scientists, Verbiscer believes that the massive geysers also created Saturn's giant E-ring—the planet's fuzzy-looking outermost ring—and sandblasted many of the other moons orbiting within it.

"[The moons] are sitting in that E-ring, and those particles [from the geysers] are being whizzed around," she said.

"They impact these satellites at a pretty high velocity. The impacts churn up the surface of these moons and create a fluffy, porous surface, which is just what you'd need to make something more reflective."

(See pictures of Saturn from NASA's Cassini mission.)

Verbiscer's team measured the reflectivity of Saturn's moons during an unusual astronomical event in which the moons lined up exactly opposite the sun as seen from Earth.

The alignment and its optimal viewing angle won't be repeated until 2049.

Enceladus's geysers have made the moon a hot spot for astronomers looking for signs of life in space.

If the geysers are drawing from pockets of water below the moon's surface, as some theories suggest, those reservoirs could harbor an intriguing variety of primitive life-forms much like those found in Earth's deep-ocean hydrothermal vents.

Amy Simon-Miller, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, cautions that we don't yet understand the nature of the geysers.

But if they do indicate liquid water, their impact on other moons raises intriguing questions about where life could exist in the solar system.

"Comets have long been considered as a possible source of water and other materials for planets," she said.

"The transport of material between moons could provide further clues about the delivery of the raw materials needed for life to the surfaces of otherwise barren worlds."

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