October 17, 2012
Evidence Of Ancient Shorelines Found On Saturn’s Moon Titan
April Flowers for redOrbit.com - Your Universe Online
What resembles a giant hot cross bun? According to radar images from NASA's Cassini spacecraft, a mysterious, nearly circular feature on Saturn's moon Titan does. The report, given at the American Astronomical Society's Division of Planetary Sciences conference suggests that there is also evidence of ancient shorelines.
"The 'hot cross bun' is a type of feature we have not seen before on Titan, showing that Titan keeps surprising us even after eight years of observations from Cassini," said Rosaly Lopes, a Cassini radar team scientist based at NASA's JPL facility. "The 'bun' may be the result of what is known on Earth as a laccolith, an intrusion formed by magma pushing up from below. The Henry Mountains of Utah are well-known examples of this geologic phenomenon."
Ellen Stofan leads another group of Cassini scientists at Proxemy Research. They have been looking at radar images of Titan's southern hemisphere because Titan is the only planetary body other than Earth that has stable liquid on its surface. Unlike Earth, Titan's liquids are hydrocarbon rather than water, and so far, scientists have only seen vast seas in Titan's northern hemisphere.
Analyzing Cassini images collected from 2008 to 2011, the new study suggests that there were once vast shallow seas around the southern pole also. Stofan's team found two possible locations for dry or mostly dry seas. The first location is about 300 by 170 miles across, and perhaps a few hundred feet deep. The second location is Ontario Lacus, the largest current hydrocarbon lake in the south. Ontario Lacus sits inside dry shorelines, looking like a shrunken version of a once mighty sea.
A third radar team, led by Oded Aharonson, at the California Institute of Technology think that Titan might have cycles like Earth's Croll-Milankovish cycles, which explain climate changes in terms of the way Earth orbits the Sun. They hypothesize that these same kinds of cycles are at play on Titan, which would cause long-term transfer of liquid hydrocarbons from one pole to the other. The south pole could have been covered by massive seas less than 50,000 years ago using this model.
"The seas on Titan are temporary hosts for experiments in prebiotic chemistry, and we know they are cycling from one hemisphere to the other over 100,000 years," said Stofan. "I'd love to get a closer look at the seas of the north or these dry seabeds to examine the extent to which this prebiotic chemistry has developed."
By analyzing Cassini radar images taken about one of Titan's seasons apart — about six Earth years — the Cassini team has confirmed the stability of Titan's northern seas. The most recent images, taken at the same time as the "hot cross bun" image, show the shorelines stayed about the same. This indicates that the northern lakes are not transient weather events, unlike a temporary darkening seen around the equator after a rainstorm in 2010.