MESSENGER is short for “MEcury Surface, Space ENvironment, Geochemistry and Ranging).

Launched on August 3, 2004, the spacecraft’s one-year mission is to study the characteristics and environment of Mercury while in orbit about Mercury, the closest planet to the Sun.

Specifically, MESSENGER will study the composition of its surface, the geologic history of the planet, its magnetic field and core, its gravitational field, and the poles of the planet.

The mission is also historic because MESSENGER will become the first human spacecraft to orbit Mercury. The Mariner 10 mission only flew by the planet, and was not inserted into orbit about the planet.

The January 14th flyby is the first flyby of the planet by the MESSENGER craft. Its closest approach on this date is scheduled to be at 2:04 p.m. Eastern Standard Time (EST) (0704 GMT) as it approaches the planet by around 124 miles (200 kilometers).

The last flyby of Mercury was done by Mariner 10 on March 16, 1975.

The flyby by MESSENGER will be the first of three flybys—January 14, October 6, both in 2008, and September 29, 2009—that will help to slow down the spacecraft so that it can accomplish an insertion into orbit about the planet on March 18, 2011.

However, the three flybys are important not only to help the spacecraft make its orbit about the planet. They are also important to astronomers who want to take measurements of the planet. During the flybys the cameras onboard MESSENGER will take hundreds of images of Mercury while approaching, encountering, and leaving the vicinity of the planet.

The MESSENGER mission is also very important because over thirty years of scientific advancements since Mariner 10 will allow scientists to learn much more about the planet than what is currently known.

Its instruments will provide the first measurements of the chemical composition of the surface of Mercury. Spectrometers (instruments that measure radiation spectrum) onboard the spacecraft will help to pinpoint the different types of minerals on the planet. Instruments to measure the gravitational field of the planet will help determine the size of Mercury's core and internal structure.

In actuality, the three flybys will give information that will be not be possible during the orbital phase of the mission.

Much more information about MESSENGER is available on the web. Three informative sites are:

NASA/Johns Hopkins University's Applied Physics Laboratory/Carnegie Institution of Washington: http://messenger.jhuapl.edu.

NASA: http://www.nasa.gov/mission_pages/messenger/main/.

NASA/Solar System Exploration: http://solarsystem.nasa.gov/missions/profile.cfm?MCode=MESSENGER.

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