Probe Detects Varying Densities in Martian Air

As NASA’s Mars Odyssey spacecraft completed its 100th orbit of the Red Planet on Wednesday, scientists were having to contend with a surprisingly fickle Martian atmosphere in guiding and slowing the robotic probe.

Since Odyssey entered orbit Oct. 23, scientists have guided the spacecraft on a series of controlled skims through the atmosphere, using the drag to slow the spacecraft and shape its orbit.

With each pass, the drag of the tenuous atmosphere shaves about five minutes from a full orbit. As of Wednesday, it was taking Odyssey 6.32 hours to whip around Mars, down from the 18.6 hours when it arrived in orbit. From orbit to orbit, however, scientists have discovered wider than expected swings in the density of the Martian atmosphere, making it harder to control the rate of slowing. The changes in density seen so far have been up to 100% and have been most dramatic over the north pole.

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Compiled by Times medical writer Thomas H. Maugh III