Map of Saturn’s largest moon reveals clues about landscape
JPL-Caltech/NASA, ASI, USGS
SAN FRANCISCO — For a frigid hunk of rock and ice more than a billion kilometers away, Titan acts a lot like Earth. Lakes and seas that adorn Saturn’s largest moon may have formed in ways similar to those that created Earth’s bodies of water, according to an analysis of the newest map of Titan’s surface.
Vast, elongated seas and smaller, roundish lakes filled with oily liquid speckle the moon’s north pole. They could be the handiwork of tectonics and sinkholes, reported geophysicist Randolph Kirk of the U.S. Geological Survey in Flagstaff, Ariz., at the American Geophysical Union’s fall meeting on December 12.
“Earth has seas, and rivers, and rain, and tectonics, and volcanism and glaciers,” Kirk said. “Titan’s got the full list from Earth, except for life.”
Scientists got their first up-close look of the big moon in 2004, when Cassini, a spacecraft orbiting Saturn, snapped radar images of Titan’s surface. The spacecraft spotted hundreds of lakes and a few large seas in 2006, but until now scientists didn’t have a full picture of Titan’s north pole.
The latest mosaic is a patchwork of coarse and fine images from Cassini’s flybys. Filling in the northern landscape’s details helped Kirk figure out the forces that may have shaped the moon’s geography.
This summer, when Kirk first looked at the new images, he noticed that the large seas seemed to cluster together. “Wow, that’s really weird,” Kirk remembered thinking. “It looks like a rectangular area.”
The seas’ coastlines run parallel to the edges of the rectangle. “When geologists see straight lines, they immediately jump to the idea of tectonics,” Kirk said.
Tectonics, or fracturing of a planetary body’s crust, carves its signature into a landscape with the same lines and angles seen around Titan’s seas, he said. The seas’ layout resembles the Basin and Range Province of western North America, a series of parallel ridges that formed when Earth’s crust stretched around 17 million years ago. On Earth, these stretch marks indicate tectonic activity, although on Titan the tectonic process may be different.
Previous researchers studying Titan’s surface had suggested that rivers might be formed via tectonics, said geophysicist Howard Zebker of Stanford University. Kirk’s data bolster the case for tectonics on this moon. Still, Zebker added, there’s a lot left to learn. “The problem with tectonics on Titan is the same as the problem with tectonics on Earth,” he said. “We don’t know what drives it.”
Another Earthlike mechanism may have formed Titan’s lakes, Kirk thinks. On Earth, water can dissolve rock and create sinkholes that fill with liquid. The resulting lakes look similar to those on Titan, he said.
If sinkholes did fashion Titan’s lakes, that may hint at another geological surprise, Kirk said. On Earth, groundwater can whittle soluble rock into caves. Similar underground caverns might exist on Titan, he said.
R.L. Kirk. Cassini RADAR observes Titan’s Kraken Mare, The largest extraterrestrial sea. American Geophysical Union Fall Meeting, San Francisco, December 13, 2013.