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Detailed Photos Reveal Clouds on Saturn's Moon Titan
By Robert Roy Britt
Senior Science Writer
posted: 02:00 pm ET
18 December 2002
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3] TITAN HAS CLOUDY POLES (pp795797) The most detailed images ever made of Saturn's moon Titan confirm earlier weather reports that suggested Titan generates clouds and thunderstorms much as Earth does. The ephemeral methane clouds at the south pole change hourly and come and go over a matter of days, presumably depositing rain onto the surface of the large moon, astronomers announced today. "These clouds appear to be similar to summer thunderstorms on Earth, but formed of methane rather than water," said Caltech researcher Antonin Bouchez. "This is the first time we have found such a close analogy to the Earth's atmospheric water cycle in the solar system." Titan is larger than the planet Mercury and is the only moon known to have a thick atmosphere. While some scientists are eager to probe Titan for possible life, others do not see it as very hospitable. Land and sea The pictures, taken with ground-based telescopes, also show an apparent surface feature on the smoggy moon that was previously detected but has never been firmly resolved. The bright continent-sized area may be a large icy highland, surrounded by dark regions that could be seas of ethane or lowlands mired in tar, scientists said. "These are the most spectacular images of Titan's surface which we've seen to date," said Michael Brown, a Caltech scientists who led one study of the images. "They are so detailed that we can almost begin to speculate about Titan's geology, if only we knew for certain what the bright and dark regions represented." The images were taken with the W. M. Keck II 10-meter and the Gemini North 8-meter telescopes atop Hawaii's Mauna Kea. Both telescopes are equipped with adaptive optics systems that adjust multiple mirrors to counter blurring effects of Earth's atmosphere. The result is pictures more detailed than those taken by a Voyager flyby of Saturn and Titan in the 1970s, the astronomers said. Previous studies had indirectly detected the clouds and also noted their disappearance, which was attributed to possible rain. The new observations actually show the clouds, which have proved difficult to make out amid the gauzy layer of smog that shrouds the moon."We see the intensity of the clouds varying over as little as a few hours," said post-doctoral fellow Henry Roe, a University of California, Berkeley scientist who led another examination of the new photographs. "The clouds are constantly changing, although some persist for as long as a few days." Roe's team will report their findings in the Dec. 20 issue of the Astrophysical Journal. The Caltech-led research is detailed in the Dec. 19 in the journal Nature. Looking for life Titan is about 808 million miles (1.3 billion kilometers) away. If there is life on the moon, it is hardy, being forced to survive surface temperatures around minus 297 degrees Fahrenheit (-183 Celsius). Microbes would also suffer a dreadful lack of oxygen. The atmosphere is mostly nitrogen, like Earth's, with significant amounts of methane. Studies of terrestrial microbes show they can be tenacious and can survive serious heat and cold.Like Earth, Titan has seasons. But because Saturn and its satellite take so long to around the Sun, the seasons are years long. It is now summer at the south pole of Titan, and the Sun has shone there continuously for six years. The added warmth is thought to fuel the clouds. A closer look at Titan is expected in 2004, when NASA's Cassini spacecraft, en route now, will visit. Cassini carries a probe, called Huygens, that it will parachute into Titan's atmosphere and land on the surface -- near the edge of the bright continent seen in the new images. A Tour of Titan
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