The new topographic map of the Titan surface, the contour lines are each 200 meters apart. (Image: NASA / JPL-Caltech / ASI / JHUAPL / Cornell / Weizmann)
He has clouds, rain, an atmosphere and even vast lakes - the Saturn moon Titan is an exception among the moons of our solar system. Although clouds and lakes are not water but methane and ethane, titanium is still considered the most earth-like world in our cosmic neighborhood. So far, however, there has been little information about what it looks like on the moon. Because its surface is denied by a dense, opaque veil all eyes. Only the radar sensors of the NASA spacecraft Cassini can penetrate it. Now, NASA researchers have created and published the first topographical map of Saturn's moon from all the data available to date on this probe. With a diameter of about 5, 150 kilometers, the Titan is larger than the planet Mercury - but much colder. Because on the surface of the moon frosty minus 178 degrees Celsius prevail. There is no liquid water on this moon. But there, another molecule has taken over the role that water has on Earth: methane. This hydrocarbon exists on the Titan in both gaseous and liquid and even frozen form - and like the water here, there is a large cycle in which the methane evaporates, rises, reacts in the atmosphere and dries off and gets into lakes the surface collects.

The existence of lakes on Titan was discovered by NASA's Cassini probe a few years ago. Their radar instruments located, especially near the Titan North Pole, flat, well-defined locations whose reflection suggested a fluid surface. This made it clear that Titan is the first known celestial body outside the earth on which lakes exist.

But because the spacecraft Cassini does not orbit the Titan, but only occasionally flies by on its way through the Saturn system past him, there was so far no map of the moon, which shows its landscape forms at a glance. "Titan has so much interesting activity - flowing fluids, migratory sand dunes - but to understand these processes, we need to know what the terrain is like, " explains Cassini card manager Ralph Lorenz of Johns Hopkins University in New York Laurel. Because the course of rivers, the formation of clouds and generally the entire weather are strongly influenced by the elevations and depressions of the landscape. "Especially for researchers studying the hydrology and climate of the moon, it is important to know whether they should start with their models of flat or high altitude, mountainous terrain, " said Lorenz.

Lowering in the polar regions and mountains on the equator display

To facilitate the exploration of the Saturn moon, NASA researchers have now for the first time created a preliminary topographic map of the titanium surface. "We did not cover more than half of the surface and had to extrapolate in many places - but we felt we could not wait until 2017 when the Cassini mission ends, " the researcher explains. Therefore, they have decided to evaluate all the data collected from 2004 to 2012 and to create a map. At the sites where there was no data, the researchers used an algorithm that determined from the height of the surrounding data points what height of the ground at that location would most likely have.

"With this new topographic map, we are now seeing three of the world's most intriguing and dynamic worlds of our solar system for the first time, " said Steve Wall of the Cassini team at NASA's Jet Propulsion Laboratory in Pasadena. The map shows, among other things, that the polar regions of the moon are shallower and lower than the area around the equator. There, numerous mountains and plateaus line up, while in the far north and south depressions dominate. In the next few years, Cassini will fly past the Titan several times and will map piece by piece the not yet recorded areas of the moon. For the time being, however, this preliminary overview map already helps to model the climate and material cycles on the Titan more precisely and thus to better understand them.

Ralph Lorenz (Johns Hopkins University, Laurel) et al., Icarus, doi: 10.1016 / j.icarus.2013.04.002 © science.de - === Nadja Podbregar

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