Monday, July 31, 2006; A05
Now Available: Lakeside lots in cool, Minnesota-like region called Xanadu. Take advantage of extremely long summer. But no smoking on the beach!
It has taken nine years, hundreds of millions of dollars and a huge amount of effort, but planetary scientists have finally found another place with a topography quite like Earth's.
On July 22, they gathered around a screen at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and saw the first detailed pictures of the high latitudes of Titan, one of the moons of Saturn.
The images were eerily familiar. What the scientists saw looked like dunes, hills, valleys and -- most unusual -- rivers running into lakes. If further studies prove that the dark, ovoid features on the vast landscape are indeed lakes, Titan will be the only body in the solar system besides Earth possessing that geological feature.
The differences between the two places, however, are as striking as their similarities.
Titan's surface temperature averages 292 degrees below zero Fahrenheit. The landscape, carved by wind and a constant drizzle, is made up largely of ice, not rock. It takes nearly 30 years for Saturn to orbit the sun, so each of Titan's seasons is a little more than seven years long.
The liquid that falls from the sky and runs down into the lakes isn't water. It is some form of liquid hydrocarbon -- very possibly methane, or what we know as natural gas. In Thursday's issue of the journal Nature, scientists reported that methane appears to fall on Titan in a constant, year-round slight drizzle.
"It is almost a parody of the Earth," said Jonathan I. Lunine, a professor of planetary science at the University of Arizona. "It is very funny to go to this place and see all these processes being played out, but with very, very different materials."
Elsewhere in the solar system -- on Mars, for instance -- there may once have been the cycles of weather and landscape-building that still exist on Earth. They ended billions of years ago. But they are still taking place on Titan, which is about one-third the size of Earth but nearly 10 times as far away from the sun.
"This tells us that we have to go a very long way from Earth to find the processes we have here," Lunine said.
The revelation comes thanks to the Cassini-Huygens spacecraft, which lifted off from Cape Canaveral on Oct. 15, 1997.
Cassini's mission, which is overseen by NASA, is the work of 17 nations. The European Space Agency built and contributed a mechanical explorer called the Huygens Probe, which parachuted onto Titan's surface on Jan. 14, 2005. Data from the probe revealed the methane drizzle reported last week.
Despite the dramatic, ringed appearance of Saturn, the environs of that huge gas planet are pretty gloomy. Saturn and its moons get one-tenth the solar radiation Earth does.
Titan's atmosphere is four times as dense as Earth's at sea level, further blocking sunlight. To top things off, it has a serious smog problem.
Hydrocarbons evaporate off Titan's surface and recondense in clouds. During that process, some molecules react with sunlight, just as happens in Earth's smoggy cities. Because there is little oxygen on Titan, the compounds are different and even more unappealing.
"They are ethane, acetylene, benzene, hydrogen cyanide -- things that go out the fume hood of an organic chemistry lab so that people don't drop dead," Lunine said.
The area with the lakes and streams, which is about the size of Australia, was first seen by the Hubble Space Telescope in 1994 through infrared imaging. It was named Xanadu.
The images gathered by Cassini this month were made with radar waves, not with visible light. The scientists are not positive the smooth, black areas in the images are liquid. But they have the same appearance that smooth bodies of water have on Earth when photographed with radar-frequency waves.
The spacecraft has time to confirm this impression with further studies. It will orbit Saturn at least until late 2008 and, perhaps, a few years longer if all goes well.
-- David Brown