At 3:14 p.m. ET Wednesday, Odyssey fired its thrusters for 25 seconds and decreased the velocity of the spacecraft by less than 2 meters per second (less than 4 miles-per-hour). On Monday, a similar 15-second firing had increased the probe's speed by a little more than 1 meter-per-second (about 2.5 miles per hour).

"These small orbit trim maneuvers complement the larger maneuvers we executed two weeks ago and tweak the orbit to get just the right altitude and ground track coverage that we desire," Mase said. "The net effect is that we move the periapsis point, the point nearest the planet, directly over the south pole and keep it there."

The mission's major goal is to map the amount and distribution of chemical elements and minerals that make up the Martian surface.

Engineers continue to check out the spacecraft systems and science instruments in preparation for the science mapping mission that will begin in February. Two of the science instruments, both neutron spectrometers that are part of the gamma ray spectrometer suite, are currently operating and collecting science data about the composition of the Mars surface.

One important task is to follow up on preliminary observations in December that indicated vast reservoirs of hydrogen near the surface, which could indicate the presence of water ice.

Odyssey Special Report