Probe of Saturn moon coming up dry

LOS ANGELES — Scientists peering through a ground-based telescope say the surface of Saturn's planet-sized moon Titan appears dry and not awash in oceans of liquid hydrocarbons as is commonly believed.

Titan — one of two moons in the solar system known to have a significant atmosphere — has long baffled scientists because it's surrounded by a thick blanket of nitrogen and methane.

Scientists have speculated that the atmospheric methane probably came from seas of liquid methane and ethane.

But telescopes and orbiting spacecraft have yet to turn up evidence of a global ocean of methane on Titan.

In the latest study, scientists using the Keck II telescope in Hawaii failed to see any reflections of sunlight that would indicate a body of liquid on the frozen moon during several viewings in 2003 and 2004, said lead researcher Robert West of the Jet Propulsion Laboratory in Pasadena.

Results appear in today's issue of the journal Nature.

The latest Earth-based observations were focused on Titan's southern hemisphere. It's possible the northern region may still contain pools of liquid organic material, West said.

Information

Nature journal: http://www.nature.com

Titan page: http://saturn.jpl.nasa.gov/home/index.cfm

"I would not say that the surface is devoid of liquid methane," he said.

Scientists believe Titan's smoggy atmosphere may be similar to that of the primordial Earth and that studying it could provide clues to how life began.

Early radar studies showed Titan was covered with pools of methane — a flammable gas on Earth but liquid on Titan because of the intense atmospheric pressure and cold.

The continuing search for oceans of liquid hydrocarbons has also proved vexing for the orbiting international Cassini spacecraft, which arrived at Saturn last year on a mission to study the ringed planets and its many moons.

Cassini has yet to detect abundant reflections that would indicate areas of liquid on Titan, but last month, Cassini photographed what appeared to be the best evidence yet of a liquid hydrocarbon lake.

The spacecraft noticed a dark spot on Titan's south pole about the size of Lake Ontario that could be the site of a past or present lake, scientists had said.

More flybys are needed to confirm the finding.