A tropical storm was not what astronomers expected to see
when they pointed their telescopes toward the equator of Saturn's moon Titan
last summer.
But that's exactly what they found on this beguiling moon,
home to a weather system both eerily
familiar and perplexingly strange. The
discovery was announced today.
In many ways Titan's climate resembles that of Earth, but
instead of a water cycle, Titan has a methane cycle. Clouds, rain
and lakes all exist on Titan, but they are all made of methane. In the
moon's frigid
climate, any water is frozen into rock-hard ice.
Shouldn't be there
Clouds of vaporized methane are not uncommon on Titan,
though they have never before been observed in Titan's tropics. But in April
2008, astronomers using the Gemini North telescope and NASA's Infrared
Telescope Facility in Hawaii spotted a severe storm covering 1.2 million square
miles (3 million square kilometers) over the equator.
"The models predicted that the equatorial region should
be very dry and should not support cloud formation," said astronomer Henry
Roe of Lowell Observatory in Arizona. "But this episode created clouds
over both the equator and the south pole. We don't know what set off that
sequence, but something gave a pretty good kick to the atmosphere."
Scientists suspect the storm's trigger may have been some
kind of geologic activity on the moon's surface, such as a geyser or new
mountain range forming. Atmospheric effects may also have set off the storm.
Whatever the cause, once the clouds were established they
seem to have spread throughout Titan's atmosphere in waves.
The situation is a new wrinkle in the study of this complex
moon.
"It's an amazing place because it is deeply familiar to
us, being from Earth, in terms of the processes - clouds forming, rainfall,
carved out channels on the surface, huge fields of what look like sand
dunes," Roe told SPACE.com. "But the materials that are involved are
quite alien."
More to learn
Scientists hope to learn more as Saturn's 30-year-long orbit
plays out a full rotation of seasons on the moon. NASA's Cassini spacecraft is
currently in orbit around Saturn, but it only flies by Titan once every six
weeks or so. In the meantime, ground-based telescopes can keep a near-steady
eye on the moon.
"We really need to keep observing Titan in detail for
many more years in order to get a true understanding of how its seasons
change," Roe said.
The researchers, led by Emily Schaller of the Institute for
Astronomy in Hawaii (now at the University of Arizona), detail the new finding
in the August 13 issue of the journal Nature.
Editor's Note: This story was updated to correct the area
measurement of the storm.
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