Sep 23, 2009

MESSENGER Set for Final Flyby of Mercury

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Sept. 23, 2009: NASA's MESSENGER spacecraft will fly by Mercury for the third and final time on Sept. 29. MESSENGER will pass less than 142 miles above the planet's rocky surface for a final gravity assist required to enter Mercury's orbit in 2011.

"This flyby is our final planetary gravity assist, so it is important for the entire encounter to be executed as planned," said Sean Solomon, principal investigator at the Carnegie Institution in Washington. "As enticing as these flybys have been for discovering some of Mercury's secrets, they are the hors d'oeuvres to the mission's main course -- observing Mercury from orbit for an entire year."

Right: Yellow lines outline the parts of Mercury to be photographed during MESSENGER's Sept. 29th flyby. Black denotes previously unseen terrain. Click on the image to view a


As the spacecraft approaches Mercury, cameras will photograph previously unseen terrain, and as the spacecraft departs it will take high-resolution images of the southern hemisphere. Scientists expect the spacecraft's imaging system to take more than 1,500 pictures. So far, more than 90 percent of the planet's surface has been photographed. These new pictures will fill in some of the gaps and provide high-resolution imagery of targets of interest.

"We are going to collect high resolution, color images of scientifically interesting targets that we identified from the second flyby," said Ralph McNutt, a project scientist at the Johns Hopkins University Applied Physics Laboratory. "The spectrometer will make measurements of those targets at the same time."


Above: A gallery of images from MESSENGER's first two flybys of Mercury. Highlights include the great Caloris impact basin, the largest volcano on Mercury, a strangely-elliptical impact scar, and a fresh crater with spider-like rays. [more]

The spacecraft may also observe how the planet interacts with the solar wind. During this encounter, high spectral- and high spatial-resolution measurements will be taken of Mercury's super-thin atmosphere and comet-like tail, which may be strongly influenced by solar activity.


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"Scans of the planet's tail will provide important clues regarding the processes that maintain Mercury's fascinating atmosphere," said Noam Izenberg of the Johns Hopkins Applied Physics Lab. "The Mercury Atmospheric and Surface Composition Spectrometer will give us a snapshot of how the distribution of sodium and calcium in Mercury's atmosphere vary with solar and planetary conditions. [We also plan to] look for several new atmospheric constituents."

An altimeter will make a topographic profile of Mercury's surface along the instrument ground track. The data will support ongoing studies of the form and structure of Mercury's craters and large faults. The information also will extend scientists' equatorial view of Mercury's global shape and allow them to confirm the discovery made during the first and second flyby that Mercury's equatorial region is slightly elliptical.

Stay tuned to Science@NASA for results from the flyby.

Editor: Dr. Tony Phillips | Credit: Science@NASA

more information

MESSENGER -- home page

The MESSENGER project is the seventh in NASA's Discovery Program of low-cost, scientifically focused missions. The Johns Hopkins University Applied Physics Laboratory of Laurel, Md., designed, built and operates the spacecraft and manages the mission for NASA's Science Mission Directorate in Washington. Science instruments were built by the Applied Physics Laboratory; Goddard; the University of Michigan in Ann Arbor; and the University of Colorado in Boulder. GenCorp Aerojet of Sacramento, Calif., and Composite Optics Inc. of San Diego provided the propulsion system and composite structure.

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