May 16, 2013
Saturn Moon Titan Topographically Mapped By Cassini
April Flowers for redOrbit.com - Your Universe Online
The first global topographical map of Saturn´s moon Titan was created by scientists at the Cassini-Huygens mission. The map, published as part of a paper in the journal Icarus, will give researchers a valuable tool for learning more about one of the most Earth-like and interesting worlds in the solar system.With a radius of approximately 1,600 miles, Titan is Saturn´s largest moon. As the second-largest moon in the Solar System, Titan is larger than the planet Mercury. Titan is of scientific interest because it is the only moon in the system known to have clouds, surface liquids and a mysterious, thick atmosphere.
Like Earth, Titan´s atmosphere is mostly nitrogen. However, the organic compound methane on Titan acts the way water does on Earth. The methane forms clouds, falls as rain and carves rivers into the surface. Methane-derived organic chemicals are present in Titan´s atmosphere, lakes and rivers, and might just offer clues about the origins of life.
"Titan has so much interesting activity - like flowing liquids and moving sand dunes - but to understand these processes it's useful to know how the terrain slopes," said Ralph Lorenz, a member of the Cassini radar team based at the Johns Hopkins University Applied Physics Laboratory (JHU-APL).
"It's especially helpful to those studying hydrology and modeling Titan's climate and weather, who need to know whether there is high ground or low ground driving their models," Lorenz said in a statement.
The thick haze over Titan scatters light in ways that make it very difficult for remote cameras — the usual method for measuring topography on planetary bodies - to “see” landscape shapes and shadows. Nearly all the data we currently have on Titan comes from NASA´s Cassini spacecraft. Cassini orbits Saturn and has flown past Titan nearly 100 times over the last ten years, using a radar imager that can peer through the haze; the radar data can be used to estimate surface height.
"With this new topographic map, one of the most fascinating and dynamic worlds in our solar system now pops out in 3-D," said Steve Wall, the deputy team leader of Cassini's radar team, based at NASA's Jet Propulsion Laboratory (JPL). "On Earth, rivers, volcanoes and even weather are closely related to heights of surfaces - we're now eager to see what we can learn from them on Titan."
Surveying Titan isn´t without challenges, however. "Cassini isn't orbiting Titan," Lorenz said. "We have only imaged about half of Titan's surface, and multiple 'looks' or special observations are needed to estimate the surface heights. If you divided Titan into 1-degree by 1-degree [latitude and longitude] squares, only 11 percent of those squares have topography data in them."
The research team used a mathematical process called splining, which effectively uses smooth, curved surfaces to “join” the areas between grids of existing data. "You can take a spot where there is no data, look how close it is to the nearest data, and use various approaches of averaging and estimating to calculate your best guess," he said. "If you pick a point, and all the nearby points are high altitude, you'd need a special reason for thinking that point would be lower. We're mathematically papering over the gaps in our coverage."
The estimations derived from splining match up with current knowledge of the moon; for example, the polar regions are known to be “lower” than areas around the equator. However, connecting those points will allow scientists to add new depth to their studies of Titan´s surface. This is especially true for those researchers modeling how and where Titan´s rivers flow, and the seasonal distribution of methane rainfall.
"The movement of sands and the flow of liquids are influenced by slopes, and mountains can trigger cloud formation and therefore rainfall. This global product now gives modelers a convenient description of this key factor in Titan's dynamic climate system," Lorenz said.
The map was compiled from data obtained in 2012. Lorenz says they should revise the map when Cassini finishes its mission in 2017. More data will be accumulated, filling in some of the gaps in the present coverage.
"We felt we couldn't wait and should release an interim product," he says. "The community has been hoping to get this for a while. I think it will stimulate a lot of interesting work."