Messenger shuts down after returning new images

A NASA spacecraft shut itself down shortly after beaming back images from a close approach of Mercury on Tuesday, its third and final flyby of the solar system's innermost planet before entering its orbit in 2011.

The Messenger probe went into "safe" mode, shutting down to prevent damage from an anomaly that engineers are now analyzing.

"I don't think anyone is concerned at this point, but any time a spacecraft goes into safe mode, you need to understand why," said Dwayne Brown, a spokesman at NASA headquarters in Washington, D.C. "It could be something very minor."

It was not immediately clear if Messenger was able to return some or all of the data from the flyby, when the spacecraft whizzed within 142 miles of Mercury.

The top picture was taken as Messenger flew about 16,700 miles above the planet; a vertical strip of the sunlit area shown at left had never before been seen.

Messenger was a bit closer -- 10,100 miles above the surface - for the lower photo.

The flyby made its closest approach at 5:55 p.m. Tuesday.

Less than two hours later, a mission update said radio signals received after the spacecraft emerged from behind Mercury indicated the spacecraft was operating "nominally," taking images and scientific measurements with seven instruments.

The flyby's primary purpose was to slow Messenger's speed by about 6,000 mph to line up its trajectory for orbit insertion planned in March 2011. The spacecraft's sun shade heated up to above 600 degrees Fahrenheit.

Messenger launched from Cape Canaveral Air Force Station in August 2004 aboard a Delta II rocket.

It is the second spacecraft to visit Mercury; Mariner 10 made three flybys in 1974 and 1975.

Messenger mission scientists plan to discuss findings from the three recent flybys - including two last year - on Thursday at Johns Hopkins University's Applied Physics Laboratory in Laurel, Md.

We'll provide an update on the spacecraft's health as soon as it becomes available.

IMAGE NOTES: At top, Mesesnger's Wide Angle Camera image shows portions of Mercury's surface that had remained unseen by spacecraft even after the three flybys by Mariner 10 in 1974-75 and Messenger's two earlier flybys in 2008. The newly imaged terrain is located in a wide vertical strip near the limb of the planet (on the left side of Mercury’s partially sunlit disk). Below: In this image, Mercury's northern horizon cuts a crisp line against the blackness of space. The surface in the lower right corner of the image is near Mercury's terminator, the line between the light dayside and dark night side of the planet. Looking toward the horizon, smooth plains extend for large distances, similar to volcanic plains seen nearby during MESSENGER's second flyby of Mercury. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.