A giant,
glassy lake larger than North America's Lake Ontario graces the south pole of
Saturn's largest moon Titan, new research confirms.
"This
is the first observation that really pins down that Titan has a surface lake
filled with liquid," said lead researcher Robert Brown of the University of Arizona's Lunar and Planetary Laboratory in Tucson.
Called Ontario
Lacus, the lake extends 150 miles (235 kilometers) and covers an area of about 7,800
square miles (20,000 square kilometers). The lake structure is filled mostly
with methane and ethane, hydrocarbons that are gases on Earth but liquid on the
bone-chilling surface of Titan.
Wet
ideas
The
finding, detailed in the July 31 issue of the journal Nature, is just
another gold star for Titan, which has become one of the most fascinating
bodies in the solar system for exploring environments that may give
rise to life. Boasting a size that's one-and-a-half times that of Earth's
moon and bigger than Mercury, Titan is the only solar system moon known to
support a planet-like atmosphere.
The idea of
liquid features on Titan is not new. Before the Cassini mission to Saturn,
astronomers thought Titan was covered in a global ocean, though the
spacecraft's flybys of the moon sucked the life out of that wet notion. Even
still, evidence for features similar to
Earth's lakes and seas, along with telltale signs of erosion from flowing
water, have since come to light.
Possible
evidence for lake-like features came from radar images, but this method can't
distinguish between liquid and very fine gravel or other tiny solids, Brown
explained.
"Detection
of liquid ethane in Ontario Lacus confirms a long-held idea that lakes and seas
filled with methane and ethane exist on Titan," said researcher Larry
Soderblom of the U.S. Geological Survey in Flagstaff, Ariz.
Titan
lake
Soderblom,
Brown and their colleagues used the infrared abilities of Cassini's visual and
infrared mapping spectrometer, or VIMS, to peer through Titan's cotton-ball-like
veil of hydrocarbons that extends more than 620 miles (1,000 km) above the
moon's surface.
The
measurements showed three features of the lake structure: the shoreline, or the
outer edge of the lake; the so-called beach just inside the shoreline, which
could be a sort of "bathtub ring" of material left behind as the
ethane mixture evaporated; and the lake's interior, which appears dark, the
researchers say.
"It
seems to have partially evaporated, and that makes sense because the south pole
has just gone through summer," Brown told SPACE.com. "The
maximum evaporation will have already occurred or is in the process of
occurring."
He added,
"There's still a lot of liquid left in that lake, and we don't think it's
going to evaporate much further."
Plus, the
lake feature could be replenished by Titan's
dreary drizzle of methane, which when hit by sunlight breaks down into
ethane.
As for how
the liquid lake feature would feel if one were to step in, "Liquid
ethane-methane mix would be less viscous than water," Brown said. "If
riffling your fingers through it you wouldn't feel as much resistance."
The Cassini
mission is an international cooperative effort of NASA, the European Space
Agency (ESA), Italian Space Agency (ASI) and several separate European academic
and industrial contributors.
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