The National Aeronautics and Space Administration spacecraft is to pass 125 miles above Mercury, taking more than 1,200 pictures. NASA said the flyby also will provide a critical gravity assist needed for the probe to become, in March 2011, the first spacecraft to orbit Mercury.
"The results from Messenger's first flyby of Mercury resolved debates that are more than 30 years old," said Sean Solomon, the mission's principal investigator from the Carnegie Institution of Washington.
During its first flyby Jan. 14, Messenger's cameras returned images of approximately 20 percent of Mercury's surface never before seen. Those images, among other things, showed Mercury's magnetic field appears to be actively generated in a molten iron core and the planet has contracted more than previously thought.
Messenger is now is more than halfway through its 4.9-billion-mile journey to enter orbit around Mercury.