From scattered,
odd-colored in-frared images taken by the Cassini spacecraft during a flyby
of Saturn’s largest satellite, scientists have been scurrying to interpret
the features of this other world. New images are now revealing what researchers
think is evidence of a large volcano on Titan that could be erupting methane.
From images taken aboard the Cassini spacecraft
during an Oct. 26 flyby of Titan, scientists are able to see a new structure
that they think could be an icy volcano, which could explain the abundance of
methane in the Saturnian moon’s atmosphere. Courtesy of NASA/JPL/University
of Arizona.
Through images collected during Cassini’s flyby last October at about 1,200
kilometers above the moon, researchers have seen what looks like a solid surface
with topographical variations, as reported in the June 9 Nature. Infrared
mapping spectrometers have penetrated through the methane-heavy haze that surrounds
Titan to reveal a roughly 30-kilometer-diameter circular structure that looks
to have two lobes “flowing” westward out of it. The structure appears
to have a dark caldera-like feature atop it, says Christophe Sotin of the University
of Nantes in France, who is lead author of the paper. Reflectance data show
that the bright and dark areas are of similar composition, he says, with the
brighter areas at higher altitudes.
Sotin and colleagues say that the structure — the first one seen from high-resolution
images from Cassini — resembles volcanic edifices on Earth and Venus. They
think it is likely a cryovolcano, an icy volcano formed by icy plumes that release
methane into the atmosphere. “We just don’t have any other viable
explanations so far,” Sotin says, “so we think it’s very possible
this is a cryovolcano.” Other scientists, however, are more skeptical.
“It looks like it could be a volcano,” says Ralph Lorenz of the Lunar
and Planetary Laboratory at the University of Arizona, Tucson, “but it
also just looks like a giant cat poo. It’s very difficult to tell with
this data.” It’s entirely possible though, he says, as Cassini radar
instruments have already detected several other features that appear to be cryovolcanic
in origin.
“I just think it may be a little too early to tell, as the images are too
low in resolution,” says Louise Prockter of the Applied Physics Laboratory
at Johns Hopkins University in Baltimore, Md. Features that are subcircular,
such as this structure, may turn out to be impact craters like those on Venus,
she says, noting how difficult it was for her team to identify evidence for
cryovolcanism on Jupiter’s moon Ganymede during the Galileo mission. Sotin
says the caldera-like dark area atop the structure could easily be an impact
crater but doesn’t think the whole structure could be one.
But, Prockter says, for now, the researchers don’t have the resolution
to tell what this structure is. “I hope it does turn out to be a volcano,”
she says. “It would be the first large icy volcano in this part of the
solar system.”
As Cassini continues its flybys of Titan — some 40 more are scheduled over
the next couple of years — the researchers will get better images and “every
dataset helps,” Sotin says. The interesting question the potential cryovolcano
might answer, Sotin and colleagues say, is how Titan’s methane is replenished.
As methane has a relatively short shelf-life in the atmosphere, for so much
to exist, it must somehow be replaced, they say. Scientists have long thought
that a large methane ocean might exist on the moon that could release methane,
but have thus far not seen conclusive evidence of a large body of liquid (see
below). A cryovolcano erupting methane would be a good explanation, they say.
Megan Sever
Read about Cassini’s latest find — a possible liquid-methane
lake — in a Web Extra posted July
1 and available in our Web Extra Archive.
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