BY DR EMILY BALDWIN
Posted: 23 June, 2009
The new orbit gains sensitivity for infrared mapping of Martian minerals by the orbiter’s Thermal Emission Imaging System (THEMIS), but at a cost, for the Gamma Ray Spectrometer (GRS) suite will no longer be operational. The GRS provided the dramatic discovery of water-ice near the Martian surface in 2002 and has also mapped global distribution of many elements, such as iron, silicon and potassium.
A recently acquired THEMIS image revealing differences in the composition and nature of a 88 by 32 kilometre portion of the southern highlands of Mars. Dark areas mark exposures of relatively cold ground with abundant bare rock, while warmer basaltic sand covers the light blue-green regions. Reddish areas likely have a higher silica content, due either to a different volcanic composition or to weathering. Image: NASA/JPL/Arizona State University.
“The orbiter is now overhead at about 3:45 in the afternoon instead of 5 p.m., so the ground is warmer and there is more thermal energy for the camera’s infrared sensors to detect,” says Mars Odyssey project scientist Jeffrey Plaut. Odyssey’s two-hour orbit is synchronized with the Sun such that the local time on the ground remains the same whatever part of Mars the spacecraft is flying over – 3:45 p.m. on the dayside or 3:45 a.m. on the nightside.
One advantage of the new orbit is that it makes for a greater temperature difference between day and nighttime measurements, which brings out more clearly the compositional variations in the surface rocks. “The new orbit means we can now get the type of high-quality data for the rest of Mars that we got for 10 or 20 percent of the planet during the early months of the mission,” says Philip Christensen of ASU’s School of Earth and Space Exploration. “At visual wavelengths, THEMIS has photographed about half of the Martian surface. We’re really looking forward to filling the holes in the coverage.”
Mars Odyssey has been orbiting the Red Planet since 2001 and has just entered a new orbit configuration to gain sensitivity for infrared mapping of Martian minerals by the orbiter’s Thermal Emission Imaging System Image: NASA/JPL-Caltech.
In another operational change, Odyssey will make more sideways-looking observations than pointing straight down, a flexible approach that will permit observations of latitudes near the poles that never pass directly underneath the orbiter. This configuration will also allow THEMIS to fill in some of the gaps left by previous imaging, and allow stereoscopic three-dimensional images to be created.
“We are using the spacecraft in a new way,” says mission manager Gaylon McSmith. In addition to extending the scientific output of the mission, Odyssey continues in its role as radio relayer for the Mars Exploration Rovers, and will also help with relaying information during NASA’s Mars Science Laboratory mission, scheduled to put the rover Curiosity on Mars in 2012.