NASA's Cassini Reveals Lake-Like Feature on Titan
Scientists are fascinated by a dark, lake-like feature recently observed on
Saturn's moon Titan. NASA's Cassini spacecraft captured a series of images
showing a marking, darker than anything else around it. It is remarkably
lake-like, with smooth, shore-like boundaries unlike any seen previously
"I'd say this is definitely the best candidate we've seen so far for a
liquid hydrocarbon lake on Titan," said Dr. Alfred McEwen, Cassini
imaging team member and a professor at the University of Arizona, Tucson.
The suspected lake area measures 234 kilometers long by 73 kilometers
wide (145 miles by 45 miles), about the size of Lake Ontario, on the
U.S. Canadian border.
Image right:This view of Titan's south polar region reveals an intriguing dark feature that may be the site of a past or present lake of liquid hydrocarbons. Image credit: NASA/JPL/Space Science Institute.
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"This feature is unique in our exploration of Titan so far," said Dr.
Elizabeth Turtle, Cassini imaging team associate at the University of
Arizona. "Its perimeter is intriguingly reminiscent of the shorelines
of lakes on Earth that are smoothed by water erosion and deposition."
The feature lies in Titan's cloudiest region, which is presumably the
most likely site of recent methane rainfall. This, coupled with the
shore-like smoothness of the feature's perimeter makes it hard for
scientists to resist speculation about what might be filling the
lake, if it indeed is one.
"It's possible that some of the storms in this region are strong
enough to make methane rain that reaches the surface," said Cassini
imaging team member Dr. Tony DelGenio of NASA's Goddard Institute
for Space Studies in New York.
"Given Titan's cold temperatures, it could take a long time for any
liquid methane collecting on the surface to evaporate. So it might
not be surprising for a methane-filled lake to persist for a long time,"
Despite earlier predictions, no definitive evidence for open bodies of
liquid has been found on Titan. Cassini has not yet been in a favorable
position for using its cameras to check for glints from possible surface
liquids in the south polar region.
"Eventually, as the seasons change over a few years, the convective
clouds may migrate northward to lower latitudes," said DelGenio, "If
so, it will be interesting to see whether the Cassini cameras record
changes in the appearance of the surface as well."
"An alternate explanation is that this feature was once a lake, but has
since dried up, leaving behind dark deposits," Turtle said. Yet another
possibility is that the lake is simply a broad depression filled by dark,
solid hydrocarbons falling from the atmosphere onto Titan's surface. In
this case, the smooth outline might be the result of a process unrelated
to rainfall, such as a sinkhole or a volcanic caldera.
"It reminds me of the lava lakes seen on Jupiter's moon, Io," Dr. Torrence
Johnson, an imaging team member at NASA's Jet Propulsion Laboratory in
"It is already clear that whatever this lake-like feature turns out to be,
it is only one of many puzzles that Titan will throw at us as we continue
our reconnaissance of the surface over the next few years," said Dr. Carolyn
Porco, imaging team leader at the Space Science Institute in Boulder, Colo.
Thirty-nine more Titan flybys are planned for Cassini's prime mission. In
future flybys the science teams will search for opportunities to observe
the lake feature again and to look for mirror-like reflections from smooth
surfaces elsewhere on Titan. Such reflections would strongly support the
presence of liquids.
The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. JPL manages the Cassini mission
for NASA's Science Mission Directorate, Washington. The Cassini orbiter
and its two onboard cameras were designed, developed and assembled at JPL.
The imaging team is based at the Space Science Institute in Boulder.
To view a computer-enhanced image of the feature and a three-frame movie
showing the evolution of nearby clouds on the Internet, visit:
Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
Erica Hupp/Dolores Beasley (202/358-1237/1753)
NASA Headquarters, Washington
Preston Dyches (720) 974-5859
Cassini Imaging Central Laboratory for Operations
Space Science Institute, Boulder, Colo.