№ 361/2009 from Dec 11, 2009
The research on Saturn's moon Iapetus is documented in a number of publications in the journals Science and Nature, where for several years, the latest findings from the cameras on the Cassini-Huygens spacecraft of Saturn and the Mars Express of Mars, have been made accessible to scientists worldwide. In the exploration of Saturn's moons, the scientists in Berlin are not only involved in the data analysis, but also crucially involved in the observation planning. For example, practically all the camera shots of Saturn's moon Iapetus were planned and prepared in Berlin.
Images from the Voyager 1 and Voyager 2 spacecrafts in 1980 and 1981 and the Cassini spacecraft since 2004 show the exact course of the brightness dichotomy on the surface. According to these images, the dark region near the equator, called the Cassini Regio, extends far into the trailing side (antapex) of Iapetus, while bright material near the pole is also found on the leading side (apex). Tilmann Denk from Freie Universität Berlin explains: "Slight temperature differences promote the sublimation of water ice, especially on the leading side. In the process dark, low-volatile material is left behind, which is further heated by solar radiation. The process reinforces itself, and after about 1 to 2 billion years the uppermost decimeters are virtually ice-free and very dark."
Critical to the emergence of the brightness dichotomy in the observed shape is the interaction with a second effect that was discovered in the image data. Due to a minimal but persistent incidence of infalling dust on the leading side of Iapetus, resulting in a light asymmetry in color and brightness, the thermally induced redistribution of water ice is not only a function of the local angle of incidence of solar radiation (thus of the latitudes of the moon), but also dependent on the longitudes and, for that reason, primarily on Iapetus's leading side. These effects are described in the two publications.
The Cassini-Huygens mission to Saturn is a joint endeavor of the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Italian Space Agency (ASI).
The Cassini research of the Remote Sensing and Planetary Sciences division of the Institute of Geological Sciences at Freie Universität Berlin is funded by the German Federal Ministry of Economics and Technology / German Aerospace Center (DLR Space Agency).