July 31, 2008

Saturn’s Titan, Like Earth, Has Surface Liquid, UA, NASA Say

By Philip Haldiman, The Arizona Daily Star, Tucson

Jul. 31--Our planet isn't the only heavenly body with liquid on its surface.

Scientists from the University of Arizona and NASA on Wednesday announced at least one of the large, lakelike features on a moon of Saturn is wet.

The moon, Titan, contains liquid hydrocarbons and ethane, scientists said.

Besides Earth, this makes Titan the only known body in our solar system with liquid on its surface, NASA said in a press release.

The lake is roughly 7,800 square miles, or about the size of Lake Ontario, though it's only about three-quarters of an inch deep. It is in the south polar region of Titan.

Scientists made the discovery using data from an instrument aboard the Cassini spacecraft that identified chemically different materials based on the way they absorb and reflect infrared light.

Before Cassini, scientists thought Titan had global oceans of methane, ethane and other light hydrocarbons.

More than 40 close flybys of Titan by Cassini showed no such global oceans exist.

Instead they found hundreds of dark lakelike features. Until now, it was not known whether these features were liquid or simply dark, solid material.

"This is the first observation that really pins down that Titan has a surface lake filled with liquid," said Bob Brown, of the University of Arizona, in the press release. Brown is the team leader of Cassini's visual and mapping instrument.

The results of the discovery are published in today's issue of the journal Nature.

Ethane and several other simple hydrocarbons have been identified in Titan's atmosphere, which is 95 percent nitrogen and 5 percent methane.

These hydrocarbons are products of atmospheric chemistry caused by the breakdown of methane by sunlight.

The ethane is in a liquid solution with methane, other hydrocarbons and nitrogen.

At Titan's surface temperatures, approximately 300 degrees below zero Fahrenheit, these substances can exist as both liquid and gas.

Titan's atmosphere makes detecting and identifying materials on the surface difficult because of a widely present hydrocarbon haze.

The detection of liquid despite unfavorable viewing conditions made the finding all the more hopeful, said Larry Soder-blom, a Cassini interdisciplinary scientist with the U.S. Geological Survey in Flagstaff.

Liquid ethane was identified using a technique that removed the interference from the atmospheric hydrocarbons.

"The fact we could detect the ethane spectral signatures of the lake even when it was so dimly illuminated, and at a slanted viewing path through Titan's atmosphere, raises expectations for exciting future lake discoveries by our instrument," Soderblom said in the press release.

"During the next few years, the vast array of lakes and seas on Titan's north pole mapped with Cassini's radar instrument will emerge from polar darkness into sunlight, giving the infrared instrument rich opportunities to watch for seasonal changes of Titan's lakes," he said.

"Detection of liquid ethane confirms a long-held idea that lakes and seas filled with methane and ethane exist on Titan."

Cassini was launched in October 1997. By the end of the mission, about 40 percent of Titan's surface will have been observed via radar, leading to a better understanding of the diverse features of the moon.

Saturn is about 10 times as far away from the sun as Earth.

NASA, the European Space Agency and the Italian Space Agency contributed to the mission.


The Cassini Mission was launched in 1997. It has provided data on the outer solar system since it arrived there in 2004.

After traveling about 3.5 billion miles in nearly seven years, Cassini, about 13,000 pounds of complex technology from home, will complete its primary mission at summer's end to explore Saturn and its moons.

Named after Giovanni Domenico Cassini, the 17th-century astronomer who discovered four of Saturn's moons, Cassini is a project of NASA, the European Space Agency and 17 countries.

Former Tucsonan Carolyn Porco is the leader of the Imaging Science team on the Cassini-Huygens mission to Saturn and Titan. She served as scientific consultant for next year's "Star Trek" film and on 1997's "Contact," starring Jodie Foster.

--Contact reporter Philip Haldiman at 573-4176 or at [email protected]


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