From FidoNet newsgroup fido.bama:
NASA’s MESSENGER probe is en route to Mercury now, and in March of 2011 it will become the first spacecraft to orbit the planet. During a year-long science mission, MESSENGER will beam back a stream of high-resolution pictures and data obtained using seven instruments designed to operate in the extreme environment near the Sun. This kind of coverage of planet #1 is unprecedented. Three flybys of Mercury by MESSENGER in 2008 and 2009 have already revealed much to be excited about.
For instance, Mercury has a long, comet-like tail, which whips around the sun in synch with the planet’s elliptical orbit, waxing and waning with Mercury’s distance from the sun. The tail is made of Mercury itself. Atoms and molecules are knocked off the planet’s surface by solar radiation, solar wind bombardment and meteoroid vaporization, forming the stuff of Mercury’s thin, elongated atmosphere (or “exosphere”). Researchers say it’s the most active planetary exosphere in the whole solar system.
MESSENGER has also found that Mercury’s magnetic field is “alive.” It is
generated by an active dynamo inside Mercury, probably akin to the magnetic
dynamo of our own planet. Buffeted relentlessly by solar wind, Mercury’s
magnetosphere is a hotbed of magnetic reconnection, the same basic physical
process that energizes auroras on Earth and sparks solar flares on the sun.
Mercury probably has its own brand of geomagnetic activity waiting to be
discovered when MESSENGER goes into orbit.
Even Mercury’s pitted landscape is interesting. Giant Caloris basin dwarfs
almost every other crater in the solar system, and it is ringed by volcanic
vents that paint the landscape with subtle but lovely colors. Towering scarps
tell a tale of a “shrinking planet” wrinkled in response to past contractions.
And the whole globe is dotted by an amazing variety of craters with names such
as Rembrandt and Picasso.
Mercury is definitely worth a look. The show begins at sunset.
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.