The Messenger -Unlocking the Secrets of Mercury

NASA's MESSENGER spacecraft is set for a historic Jan. 14 flight past Mercury that will explore some of the last major "white space" -the unseen terrain on the map of the inner solar system. Image above is sunrise on Mercury.

MESSENGER, launched in 2004,  is the first NASA mission sent to orbit Mercury, the planet closest to the sun. But on Jan. 14 it will pass close by the planet  and use Mercury's gravity for a critical assist needed to keep the spacecraft on track for its ultimate orbit around the planet three years from now. Still, the spacecraft is also expected to throw back some never-before –seen images, NASA said.  The flyby also will gather essential data for planning the overall mission. After flybys of Earth, Venus, and Mercury, it will start a year-long orbital study of Mercury in March 2011, NASA said.

Specifically MESSENGER has two cameras -- one wide-angle, and one narrow-angle -- to help the "two-eyed" Mercury Dual Imaging System (MDIS) create a map of the planet's landforms, NASA said.   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. Once MESSENGER does orbit 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.

A 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, NASA said.

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. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) will be able to determine Mecury’s atmosphere and also detect minerals on the surface. The instrument is extremely sensitive to light from the infrared to the ultraviolet, NASA said.

Until now, NASA’s Mariner 10 was the first and only spacecraft to reach Mercury, according to NASA’s Web site.  Mariner 10 flew to within 460 miles of Mercury on March 29, 1974. It swept past the planet again on Sept. 24, 1974, and on March 16, 1975. During those flights, the spacecraft photographed portions of the surface of Mercury. It also detected Mercury's magnetic field, according to NASA’s Web site.

Posted by Josh Hill.