Messenger ready for final Mercury flyby

WASHINGTON, Sept. 23 (UPI) -- NASA says its Messenger spacecraft will make its third and final flyby of Mercury next Tuesday.

The Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft known as Messenger will pass less than 142 miles above the planet's rocky surface for a final gravity assist that will enable it to enter Mercury's orbit in 2011, the space agency said.

Determining the composition of Mercury's surface is a major goal of the orbital phase of the mission, NASA said, noting the spacecraft already has imaged more than 90 percent of the planet's surface. The Messenger team will activate instruments during next week's flyby to view specific features to uncover more information about Mercury.

"This flyby will be our last close look at the equatorial regions of Mercury, and it is our final planetary gravity assist, so it is important for the entire encounter to be executed as planned," said Sean Solomon, the project's principal investigator at the Carnegie Institution in Washington. "As enticing as these flybys have been for discovering some of Mercury's secrets, they are the hors d'oeuvres to the mission's main course -- observing Mercury from orbit for an entire year."

The spacecraft has completed nearly three-quarters of its 4.9-billion-mile journey to enter orbit around Mercury. The trip includes more than 15 trips around the sun.