On Saturn's moons, some unexpected hints of water

Cassini flyby reveals water vapor in plume from Enceladus. A hidden ocean on Titan?

By Peter N. Spotts | Staff writer of The Christian Science Monitor

from the March 27, 2008 edition

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In the hunt for exciting destinations in space – especially those that may be hospitable to simple forms of life – you would need to travel no farther than Saturn and its moons Enceladus and Titan.

The more the craft Cassini flies past these two moons, the more tantalizing they become as targets for follow-up missions. "We've got to find a way to get back there," says Hunter Waite Jr., a space physicist with the Southwest Research Institute (SwRI) in San Antonio.

In Cassini's latest encounter with Enceladus, the orbiter zipped through a plume of dust, ice, and gas erupting from its south pole. Findings released Wednesday show this plume contains far larger quantities of water vapor than researchers had expected. US and European scientists also found in the plume a smorgasbord of organic chemicals, including methane, acetylene, formaldeyhde, and hydrogen cynanide.

Indeed, the plume's chemistry more closely resembles the primitive materials found in a comet than the more heavily processed chemicals one might expect to see in a mature moon, researchers say.

"To have primordial material coming out from inside a Saturn moon raises many questions on the formation of the Saturn system," says Dr. Waite, lead scientist for one of the Cassini orbiter's instruments.

From a biological standpoint, "the organics are there," he says. Whether liquid water – another key ingredient for organic life – is present beneath the surface remains an open question, he says.

Temperatures at the south pole, the plume's source region, suggest that liquid water may be present close to the moon's icy surface, adds John Spencer, another Cassini scientist with SwRI.

The geysers that are feeding the plume at supersonic speeds originate from four long fissures, dubbed the tiger stripes. These rifts are warmer than the surrounding moonscape, though the temperatures are frigid by Earth standards. The region surrounding these rifts is chilled to minus 343 degrees F., compared with temperatures of up to minus 126 degrees F. along the fissures, Dr. Spencer says.

But with the 217-degree difference, "it starts to look like there's liquid water not too far down in order to get temperatures up as high as this."

In addition, the team discovered more hot fissures near the tiger stripes. The heat source: largely friction within the moon as Saturn's gravity tugs on Enceladus as it travels in its slightly elliptical orbit around the planet.

Titan's hidden ocean?

On Tuesday, Cassini was making its 42nd science flyby Titan, Saturn's largest moon. There, Cassini has uncovered evidence that the moon's crust is blowing in the wind – literally. The implication: The crust may be riding on a global layer of liquid roughly 62 miles below the surface.

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