At 4:41 a.m. on October 6--for the second time in less than a year--NASA's MESSENGER spacecraft will swoop just 125 miles (200 kilometers) above the cratered surface of Mercury, snapping hundreds of pictures and collecting a variety of other data from the planet as it gains a critical gravity assist that keeps the probe on track to become the first spacecraft ever to orbit the innermost planet beginning in March 2011.

Reporters are invited to the MESSENGER Situation Room at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., to watch operators maneuver the spacecraft through closest approach from 4:00 a.m. - 6:00 a.m. ET on Monday, October 6, 2008. Members of the MESSENGER operations and science teams will be available to discuss the mission and Mercury flyby activities. Space is limited and registration is required. Reporters interested in attending should contact Paulette Campbell at (240) 778-6792 or Paulette.Campbell@jhuapl.edu by October 3, 2008.

This flyby event, along with one additional pass by Mercury and two deep-space maneuvers, will slow the spacecraft sufficiently to allow it to be inserted into orbit around Mercury on March 18, 2011. This flyby promises to reveal new and unexpected discoveries, as MESSENGER images 30 percent of the surface previously unseen by spacecraft. Its instruments will capture more than 1,287 images of the planet, and the team will begin to make additional progress on the mission goals to:

• Map the elemental and mineralogical composition of Mercury's surface;
• Image globally the surface at a resolution of hundreds of meters or better;
• Determine the structure of the planet's magnetic field;
• Measure the planet's gravitational field structure; and
• Characterize exosphere neutrals and accelerated magnetosphere ions.

Much of the science data from close approach will be sent back to Earth in the days following the flyby, and scores of images will be transmitted and made available on the MESSENGER and NASA websites.

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a NASA-sponsored scientific investigation of the planet Mercury and the first space mission designed to orbit the planet closest to the Sun. The spacecraft launched on August 3, 2004, and after flybys of Earth, Venus, and Mercury, will start a yearlong study of its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the mission as principal investigator. The Johns Hopkins University Applied Physics Laboratory built and operates the MESSENGER spacecraft and manages this Discovery-class mission for NASA. Visit http://messenger.jhuapl.edu/ for the latest images from Jupiter and mission status reports.