After cruising across 460 million kilometers of interplanetary space over 6½ months, NASA's 2001 Mars Odyssey spacecraft reached the red planet yesterday. The spacecraft was "captured" into a looping 18.7-hour orbit after being slowed by a 20-minute-long rocket firing beginning at 7:23 p.m. Pacific time (2:23 Universal Time on October 24th). Most of the burn occurred with the spacecraft behind Mars and out of communication with Earth, and once radio contact was reestablished, anxious engineers determined that the complicated maneuver was executed flawlessly. "Hundreds and hundreds of things had to go right," noted project manager Matt Landano, "and they did." In fact, analysis shows that the spacecraft hit its target, 300 km above the Martian surface, to within 1 km.

The success of this all-important orbit maneuver is helping ease painful memories of NASA's two previous Mars missions, each of which failed just as it reached the planet. On September 23, 1999, the Mars Climate Orbiter entered the planet's atmosphere too low upon arrival — due to an infamous mixup involving metric-English conversions — and likely burned up. Ten weeks later, on December 3rd, Mars Polar Lander and its hitchhiking payload of two Deep Space 2 probes disappeared without a trace as they descended to the surface and presumably crashed.

Thus, Mars Odyssey represents a chance at redemption for NASA and its outgoing administrator, Daniel Goldin. In the weeks ahead, the spacecraft will pass through the planet's thin upper atmosphere some 380 times, using air friction to gradually bleed off velocity and altitude. By February the craft should be in its final, circular orbit, traveling pole to pole at an altitude of 400 km. Then its scientific survey work will begin. Mars Odyssey carries an infrared imaging system, called THEMIS, that will use infrared spectroscopy to determine the composition of mineral deposits on the surface. THEMIS is designed to work in concert with the spacecraft's gamma-ray spectrometer, which should map the abundance of hydrogen just below ground level (hydrogen is a proxy for the presence of water). A third experiment, for studying the planet's radiation environment, failed to respond to commands from Earth in August and has been shut down.