The insertion into orbit starts at about 9 p.m. ET on March 17. From that point on, Messenger will fly a 12-hour orbit at a minimum altitude of about 124 miles. The spacecraft's science instruments will be turned on and checked out starting on March 24.
The primary science phase begins April 4 and will last about one year; during that time, Messenger is expected to gather more than 75,000 images.
In this mosaic of what NASA calls the "eastern limb" of Mercury, from the January 2008 flyby (the first of the three by Messenger), the large gold-hued circular area is the Caloris basin, notable for its volcanic plains. The basin is about 960 miles in diameter, and Messenger was passing by at a distance of about 8,000 miles.
The name "Messenger," by the way, stands for a much longer phrase: MErcury Surface, Space ENvironment, GEochemistry, and Ranging.
The diameter of Mercury is 3,030 miles.