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'Thunderstorms' spotted on Saturn moon

Methane clouds not seen in 1980 probe images

By Richard Stenger

The light-colored area near Titan's south pole is a methane cloud.
The light-colored area near Titan's south pole is a methane cloud.

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(CNN) -- Bright patches of methane have been detected swirling around the southern pole of Titan, settling a longstanding question as to whether Saturn's largest moon possesses clouds, according to a new study.

The discovery was made with two large telescopes in Hawaii, using new adaptive optics to distinguish features on the haze-shrouded satellite that even a visiting spacecraft had missed.

Titan, bigger than the planet Mercury, is the only moon in the solar system with a dense atmosphere, which has been compared to that covering our planet before life arose.

"These clouds appear to be similar to summer thunderstorms on Earth, but formed of methane rather than water," said Antonin Bouchez of the California Institute of Technology, co-author of an article in the December 19 issue of the journal Nature.

"This is the first time we have found such a close analogy to the Earth's atmospheric water cycle in the solar system," Bouchez said.

No clouds had turned up in previous searches, but recent data suggested that they existed. That theory, however, seemed to contradict visual evidence from Voyager 1.

In 1980, the passing NASA probe took close-up photos of Titan, which appeared cloaked in a featureless, uniform haze.

By ramping up the vision of the W. M. Keck II and Gemini North telescopes atop the Mauna Kea volcano, two astronomical teams were able to see atmospheric features on the moon with unprecedented clarity.

Details as small as 186 miles (300 km) across can be seen, from a distance of about 820 million miles (1.3 billion km). The feat is the equivalent of reading an automobile license plate 63 miles (100 km) away, according to the researchers.

"We see the intensity of the clouds varying over as little as a few hours. The clouds are constantly changing, although some persist for as long as a few days," said University of California, Berkeley astronomer Henry Roe, lead author of a related report in the December 20 issue of Astrophysical Journal.

Titan's atmosphere is composed mostly of nitrogen, like ours. But in other ways it is extremely inhospitable. It lacks oxygen, an indicator of terrestrial life.

Moreover, it contains significant quantities of methane and other hydrocarbons, rendering it a natural brew of noxious smog.

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