Washington: The first global topographic map of Saturn`s largest moon Titan has been created, giving researchers a valuable tool for learning more about one of the most Earth-like and interesting worlds in the solar system.
At 1,600 miles (2,574 kilometers) across, Titan is bigger than planet Mercury and is the second-largest in the solar system.
Scientists care about Titan because it`s the only moon in the solar system known to have clouds, surface liquids and a mysterious, thick atmosphere.
The cold atmosphere is mostly nitrogen, like Earth`s, but methane on Titan acts the way water vapor does on Earth, forming clouds and falling as rain and carving the surface with rivers. Organic chemicals, derived from methane, are present in Titan`s atmosphere, lakes and rivers and may 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, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., 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," Lorenz stated.
Titan`s thick haze scatters light in ways that make it very hard for remote cameras to "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 Saturn-orbiting Cassini spacecraft, which has flown past the moon nearly 100 times over the past decade.
On many of those flybys, Cassini has used a radar imager, which can peer through the haze, and the radar data can be used to estimate the surface height.
There are 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."
Lorenz`s team used a mathematical process called splining-effectively using smooth curved surfaces to "join" the areas between grids of existing data.
The estimations fit with current knowledge of the moon-that its polar regions are "lower" than areas around the equator, for example-but connecting those points allows scientists to add new layers to their studies of Titan`s surface, especially those modeling how and where Titan`s rivers flow, 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 noted.