Mercury, it's time for your close-up.

NASA's Mercury MESSENGER probe will shoot more than 1,200 photographs Monday as it flies by Mercury on its 4.9-billion-mile (7.9-billion-kilometer) journey that will eventually place it in orbit there 30 months from now. Scientists hope the photos will reveal more about the composition of Mercury; they will include images of regions on the planet's surface heretofore unseen.

This will be the second of three flybys of Mercury, the solar system's smallest planet (now that Pluto is no longer counted as one) and the world closest to the sun—a factor that's made it difficult to study from Earth.

Measurements taken by the spacecraft's magnetometer in a January pass indicated that Mercury's magnetic field may be generated by a large molten-iron core. Images showed that Mercury's plains resulted from volcanic eruptions, and that the planet has shrunk more than scientists previously believed.

"This second flyby will show us a completely new area of Mercury's surface, opposite from the side of the planet we saw during the first," Louise Prockter, an instrument scientist for the spacecraft's Mercury Dual Imaging System, said in a press release.

The flyby is more than a photo shoot, though. MESSENGER will also use Mercury's gravity to position itself for a March 2011 insertion into the planet's orbit—the first time a spacecraft will circle Mercury.
MESSENGER is an acronym for MErcury Surface, Space ENvironment, GEochemistry and Ranging. Its journey to Mercury uses the gravitational assist from three planets and includes more than 15 trips around the sun. After its August 2003 launch, MESSENGER flew by Earth in August 2005 as well as Venus in October 2006 and June 2007.

(Image of Mercury cliffs and craters/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)