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MESSENGER Mission News
June 22, 2012

MESSENGER Completes Its 1,000th Orbit of Mercury
MESSENGER will complete its 1,000th orbit of the planet closest to the Sun at 11:22 p.m. EDT tonight. "Reaching this milestone is yet another testimony to the hard work and dedication of the full MESSENGER team that has designed, launched, and operated this highly successful spacecraft," says the mission trajectory lead Jim McAdams of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md.

The spacecraft was inserted into orbit around Mercury in mid-March 2011, after travelling more than 15 times around the Sun through the inner solar system and completing six planetary flybys. "Since arriving at Mercury, MESSENGER took a little more than 15 months to reach this mark," McAdams notes. "But because the orbital period has been reduced from just under 12 hours to 8 hours, it will take only 11 months to complete the next 1,000 orbits."

During its primary mission, which concluded on March 17, 2012, MESSENGER performed the first global reconnaissance of the geochemistry, geophysics, geologic history, atmosphere, magnetosphere, and plasma environment of Mercury. The spacecraft is now more than one-quarter of the way into a one-year extended mission that is building on this knowledge to address new questions raised by the initial orbital observations.

"Mercury is in a tough neighborhood, with high temperatures and increasingly frequent streams of solar energetic particles," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "It is therefore all the more remarkable that this spacecraft has met the challenge to perform as designed after 1,000 orbits about the innermost planet in our solar system. There is much more science ahead for this mission."

Paper on MESSENGER's Magnetosphere Garners Top Student Presentation Award

University of Michigan graduate student and MESSENGER team member Gina DiBraccio received an Outstanding Student Paper Award from the American Geophysical Union's Planetary Sciences Section for her presentation, "MESSENGER observations of magnetopause structure at Mercury," delivered at the AGU Fall Meeting in San Francisco last December. The presentation explored the mechanism by which energy and momentum are transferred from the solar wind into Mercury's magnetosphere.

"The processes at the boundary to Mercury's magnetosphere, in particular magnetic reconnection, are similar to what has been found at Earth's magnetopause, except that Mercury experiences much shorter timescales and a higher frequency of events," explains DiBraccio. "This has led us to question what causes the difference in timescales and intensity of magnetopause magnetic reconnection at various planets. We find that the changes in plasma and magnetic pressures affect solar-planetary interaction throughout the heliosphere, as do the orientation and strength of the interplanetary magnetic field that drapes around the planetary magnetopause."

DiBraccio's interest in space science dates back to the third grade, when she declared that she wanted to be an astronaut. "After noticing my decision, my parents strongly supported and encouraged me," she says. "They would leave daily news clippings regarding NASA and new discoveries, take me to the local planetarium and observatories, and bring me to special events at museums, and they even bought me a telescope."

She attended the University of Pittsburgh, earning a dual B.S. degree in physics and astronomy, as well as a B.S. in business administration. She also worked as a co-op student at the NASA Glenn Research Center in Cleveland, Ohio, and then later at the NASA Goddard Space Flight Center in Greenbelt, Md.

DiBraccio is now working on a Ph.D., and she plans to continue research with MESSENGER data. "There are many outstanding questions pertaining to planetary magnetospheres, and MESSENGER makes it possible to explore this exciting topic so we may compare our results to those at other planets with intrinsic magnetic fields," she says.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and entered orbit about Mercury on March 17, 2011 (March 18, 2011 UTC), to begin a yearlong study of its target planet. MESSENGER's extended mission began on March 18, 2012. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as Principal Investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA.

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