MESSENGER captures new images of Mercury during a third passage

NASA craft gets first detailed views of some parts of the planet

Flying within 228 kilometers of the surface of Mercury on September 29, the MESSENGER spacecraft snapped portraits of a portion of the planet that had never before been imaged close-up.

PLANET PIN-UP The MESSENGER spacecraft has imaged previously unimaged terrain of Mercury, outlined in red here, and located in a wide vertical strip near the left edge of the planet. A newly imaged impact basin and the Rembrandt basin are also labeled. NASA, Johns Hopkins University Applied Physics Laboratory, Carnegie Institution for Science

The September 29 encounter was the third and last flyby and gave the craft the gravitational assistance it needs to settle in March 2011 into a yearlong orbit around Mercury, the solar system’s innermost and least explored planet.

The first images from the latest encounter, which detail 5 percent of the planet that hadn’t been examined by spacecraft before, were released on September 30 and more are expected over the next few days.

The craft did have some trouble, however. MESSENGER unexpectedly went into hibernation mode, shutting down all observations, when it passed within 800 kilometers of Mercury, shortly before reaching its closest approach. That shutdown, which lasted nearly seven hours, prevented radio observations and altimeter measurements that were to be taken during closest approach. Also prevented were the most sensitive observations with the craft’s gamma ray and neutron spectrometer, designed to record the chemical composition of the planet’s crust.

In addition, observations planned for just after closest approach, including infrared and visible-light portraits of the surface and studies of Mercury’s thin atmosphere, were also not possible, notes MESSENGER principal investigator Sean Solomon of the Carnegie Institution for Science in Washington, D.C.

“We are disappointed that a number of our special targeted observations were not completed, but the spacecraft and payload are healthy and the primary objective of the flyby — to head the probe toward insertion into orbit about Mercury in March 2011 — was successfully accomplished,” says Solomon. 


A camera on MESSENGER homed in on the sunlit portion of Mercury’s northern horizon. The surface at the lower right corner in this image is near Mercury’s terminator, the line between the day and night side of the planet. Toward the horizon, smooth plains extend for large distances, similar to plains imaged during MESSENGER’s second flyby of Mercury in October 2008.

Credit: NASA, Johns Hopkins University Applied Physics Laboratory, Carnegie Institution for Science


This impact basin on Mercury was imaged for the first time by the MESSENGER spacecraft during its third flyby. The basin has a double-ring structure and its outer diameter is about 260 kilometers. The basin’s floor consists of smooth material and shows concentric troughs, which are rare on Mercury.

Credit: NASA, Johns Hopkins University Applied Physics Laboratory, Carnegie Institution for Science

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