An aging but dependable NASA probe has tweaked its orbit around Mars to seek out warmer ground on the distant, red world.

NASA reckons the infrared cameras aboard the Mars Odyssey spacecraft will work better over regions exposed to more sunlight, so it shifted the probe's orbit in order to steer its camera eyes away from the evening shade. The move took nearly eight months, , but Odyssey's infrared camera now peers onto the planet during the Martian afternoon, earlier than it has during most of its seven-year mission.

"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," said Jeffrey Plaut planetary scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in a statement.

The orbital switch increases the sensitivity of the camera, called the Thermal Emission Imaging System, to allow for better mapping of Martian minerals. It now senses infrared radiation from a warmer surface that is receiving more sunlight.

A warmer Martian target

Temperatures on Mars range from as low as minus 195 degrees Fahrenheit (-125 degrees Celsius) near the poles during the winter to 70 degrees Fahrenheit (20 degrees Celsius) at noon near the equator. The average Martian temperature is about  minus 80 degrees Fahrenheit (-60 degrees Celsius).

On Sept. 30, 2008, Odyssey fired its thrusters for six minutes, entering into a "drift" pattern that gradually changed its orbit and the time-of-day during which it was over the planet. On June 9 of this year, the spacecraft fired the thrusters again, this time for 5.5 minutes. The burn ended the drift pattern and locked the spacecraft into the new orbit, always above the planet in the mid-afternoon.

"The maneuver went exactly as planned," said JPL's Gaylon McSmith, Odyssey mission manager.

Afternoons on Mars

This is not the first time the orbiter will see a sunnier side of Mars. Back in 2002, early in Odyssey's mission, it flew mid-afternoon passes over the planet and made important discoveries of minerals, including salt deposits that were apparently left behind by large bodies of water when they evaporated.

"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 those early six months," said Philip Christensen, an Arizona State University researcher who is principal investigator for Odyssey's Thermal Emission Imaging System.

The trade-off is that the new orbit will put one of the spacecraft's other instruments out of commission. The gamma-ray detector, one of a suite of three instruments that sense short light waves and neutrons, must be shut down or risk overheating. In 2002, the suite, called the Gamma Ray Spectrometer, made a dramatic discovery of large areas of water-ice near the Martian surface. The gamma ray detector has also mapped the global deposits of many elements, such as iron, silicon and potassium.

NASA launched the Mars Odyssey orbiter in 2001. The solar-powered spacecraft arrived at the red planet about a year later to begin its now seven-year Mars observation campaign.

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