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Mercury, Get Ready for a Close-Up
Planet Mercury better be ready for its close-up.

The pioneering MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) mission will orbit the mysterious terrestrial planet, looking closely at its surface, its crust, its atmosphere -- even its magnetic field.

Loaded with seven advanced scientific instruments and one radio science experiment to pack in as much science as possible, the spacecraft makes the most of the first mission to Mercury since 1975. One of MESSENGER's goals is to learn as much as possible about Mercury's topography -- its barren, pockmarked surface. Three scientific instruments were specially designed to study Mercury's surface.

Spacecraft with different payload parts highlighted.Image to left: The pioneering MESSENGER spacecraft and its array of scientific equipment will tell us more about mysterious Mercury than we have ever known. Credit: JHUAPL

Two cameras -- one wide-angle, and one narrow-angle -- will help the "two-eyed" Mercury Dual Imaging System (MDIS) create a map of the planet's landforms. It will also trace different features on the surface. A special pivoting platform allows scientists to point the MDIS in whatever direction they choose.

The Mercury Laser Altimeter (MLA) will create topographic maps of the planet's surface in unprecedented detail. When the laser shines down and reflects off Mercury's surface, a sensor will gather the light, allowing scientists to track variations in the distance from the surface to the spacecraft.

As MESSENGER orbits Mercury's surface, the spacecraft will be attracted to areas where the mass is greater and gravity tugs a little harder, causing it to speed up slightly as it approaches and slow a bit as it recedes. The Radio Science experiment will use the Doppler Effect to track the changes in MESSENGER's velocity, and translate them into clues to how the planet's mass is distributed and where the crust is thicker or thinner.

Mercury gets as close as 57 million miles from Earth, but MESSENGER's mission profile calls for the spacecraft to travel nearly five billion miles to get there. MESSENGER isn't traveling all that distance just to get a good look at Mercury's topography. Three instruments will rely on a process called spectroscopy to tell scientists what elements are present in the rocks and minerals around the planet.

The X-ray Spectrometer (XRS) will detect X-rays emitted by certain elements in Mercury's crust. The Gamma Ray and Neutron Spectrometer (GRNS) works in much the same way, detecting gamma rays and neutrons emitted by various elements. GRNS may also help to determine if water ice really exists in permanently-shadowed craters at the planet's north and south poles -- as previous observations suggest.

MESSENGER rests on a processing standBut what gases might be present in Mercury's atmosphere? The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) will be able to determine this and also detect minerals on the surface. The instrument is extremely sensitive to light from the infrared to the ultraviolet.

Image to right: A technician checks the MESSENGER spacecraft after its move to a workstand at Astrotech Space Operations in Titusville, Fla., where final assembly and testing were completed. Credit: NASA/KSC

Some planets have a magnetic field that influences the behavior of electrically charged particles. The source of Mercury's field is not understood. MESSENGER's Energetic Particle and Plasma Spectrometer (EPPS) will measure the composition, distribution and energy of electrons and ions in Mercury's magnetosphere, the region surrounding the planet that is controlled by its magnetic field. Perched at the end of a nearly 12-foot-long boom, the Magnetometer (MAG) will map the planet's magnetic field and search for magnetized rocks in the crust.

Together, MESSENGER's advanced scientific instruments will shed light on how a terrestrial planet evolves, telling us more about our planet's own past. Whether Mercury is ready or not, the mission will give us a new look at our least-explored terrestrial neighbor, from the inside out.

For further information, visit:
The John Hopkins University's MESSENGER Web Site
Anna Heiney
NASA's John F. Kennedy Space Center