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Dive Into Saturn Moon's Jets Shows Ingredients for Life

Victoria Jaggard
National Geographic News
March 26, 2008
 
Water, heat, and now organic materials—three of the basic ingredients for life as we know it—have all been confirmed on Saturn's moon Enceladus, scientists announced today.

The new data come from the closest flyby of the moon yet by NASA's Cassini spacecraft.

The probe flew through the plumes of ice and gas that jet out of Enceladus's south polar region on March 12, skimming just 32.3 miles (52 kilometers) above the surface.

"The density [of material] increased dramatically as we moved over the plume," Cassini team member Hunter Waite, of the Southwest Research Institute in San Antonio, Texas, said at a press briefing. "But water was not the only constituent we saw."

The probe also "tasted" methane and other organics within the jets at levels 20 times higher than expected, as well as carbon monoxide and carbon dioxide.

"The composition of the plume is very much like the composition of a comet," Waite noted.

Comets can contain primordial materials, so many scientists think the objects might have seeded life on Earth.

The presence of similar materials on Enceladus therefore raises questions about the possibilities for life within the Saturnian system, he said.

Hot Stripes

Before the flyby, scientists had used ultraviolet imaging on board Cassini to study the structure and composition of the plume and decide whether it would be safe for the craft to fly through.

Previous studies had revealed that plumes are shooting out of the moon at about 650 to 1,100 miles (1,046 to 1,770 kilometers) an hour, originating from fractures at the south pole known as tiger stripes.

Last October the team watched as a transiting star called zeta Orionis moved behind the gassy plumes.

Changes in the starlight's intensity allowed the scientists to "see" four distinct high-density jets of steam within the broader clouds of gas, said team member Larry Esposito of the University of Colorado at Boulder.

Despite the jets' high speed, researchers calculated that the density and size of materials mean "the gas and particles are not a danger to Cassini," Esposito said.

Scientists slated the probe to fly through the plumes at an angle, approaching from the north and skirting southward along the edge.

The flyby gave scientists the most detailed view yet of heat coming from the tiger stripes.

Cassini's first Enceladus flyby in March of 2005 had captured images showing that the area around the fractures was much warmer than the surrounding surfaces.

"There was a very bright glow of heat coming out of the south polar region" in the 2005 images, Cassini co-investigator John Spencer of the Southwest Research Institute in Boulder, Colorado, said at the briefing.

(Related news: "Saturn's Icy Moon May Have Been Hot Enough for Life, Study Finds" [March 13, 2007].)

With the latest flyby, "now we see heat coming out of each of those fractures individually."

In fact, the warmest points along the fractures correspond to where two of the four jets originate.

Of course, warmth is a relative term on a moon like Enceladus, Spencer said.

The fractures are about -135 degrees Fahrenheit (-93 degrees Celsius)—downright balmy compared with the surrounding temperature of -300 degrees Fahrenheit (-184 degrees Celsius).

But the fact that heat is escaping through the tiger stripes suggests that it's even warmer under the moon's surface, he said.

"It's entirely possible there's going to be liquid water not too far below these tiger stripe fractures."

Lights Out

Unfortunately, a software glitch prevented the craft's Cosmic Dust Analyzer from taking measurements during the closest part of the approach.

Researchers had hoped that the instrument would collect better data on particles of sodium and silicon detected in the plumes during previous observations, Esposito told National Geographic News.

The probe also couldn't take new close-up visible-light images of the moon, Spencer said, because the flyby happened as Enceladus passed into Saturn's shadow.

(See pictures of Saturn and some of its moons.)

"The lights went out, so we couldn't take any pictures—at least not any good ones," he said.

Two upcoming Enceladus flybys in October will therefore be dedicated to dust sampling and imaging.

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