Cassini creates the first global topographic map of Titan
Sen—Scientists from NASA's Cassini radar team have created the first global topographic map of Saturn's moon Titan.
Titan's thick haze means remote cameras can't "see" landscape shapes and shadows, the usual approach to measuring topography on planetary bodies. Virtually all the data we have on Titan comes from NASA's Cassini spacecraft, which has flown past the moon almost 100 times over the past decade. On many of those flybys, Cassini used a radar imager to peer through the haze, to estimate the surface height.
"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, Maryland, who led the map-design team. "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."
"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, deputy team lead of Cassini's radar team, based at NASA's Jet Propulsion Laboratory in California. "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."
The upper panel of this graphic show where radar images have been obtained over almost half of Titan's surface.The lower panel shows the new topography map. Image credit: NASA/JPL-Caltech/ASI/JHUAPL/Cornell/Weizman
"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."
Lorenz's team used a process called splining, 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."
These polar maps show the first global, topographic mapping of Saturn's moon Titan, using data from NASA's Cassini mission. Image credit: NASA/JPL-Caltech/ASI/JHUAPL/Cornell/Weizmann
The estimations fit with current knowledge of the moon. Its polar regions are "lower" than areas around the equator, but connecting those points allows scientists to add new layers to their studies of Titan, especially those modelling Titan's rivers, and the seasonal distribution of its 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.
Lorenz hopes to revise the map when the Cassini mission ends in 2017 when more data is available. "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."
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. Cassini was launched in 1997 and entered Saturn's orbit in 2004. The Huygens space probe was launched with Cassini and landed successfully on Titan in 2005. Cassini continues to provide much information and stunning images of Saturn, its rings and its moons.