The National Aeronautics and Space Administration's Mercury Surface, Space Environment, Geochemistry, and Ranging, or MESSENGER, spacecraft also returned hundreds of new photos and measurements of the planet's surface, atmosphere and magnetic field.

The spacecraft flew by Mercury shortly after 4:40 a.m. EDT, Oct. 6, completing a gravity assist maneuver to keep it on course to orbit Mercury again in 2011.

"The region of Mercury's surface that we viewed at close range for the first time this month is bigger than the land area of South America," said Sean Solomon, the mission's principal investigator and director of the Department of Terrestrial Magnetism at the Carnegie Institution of Washington. "When combined with data from our first flyby and from Mariner 10, our latest coverage means that we have now seen about 95 percent of the planet."

Scientists said the spacecraft's science instruments took more than 1,200 pictures of the surface, while topography beneath the spacecraft was profiled with a laser altimeter.

MESSENGER is the seventh in NASA's Discovery Program of lower-cost, scientifically focused missions.