NASA spacecraft to make historic flyby over Mercury

They expect to harvest some 1,200 images and other data from instruments aboard the MESSENGER spacecraft that could shake up the study of the solar system, officials said Thursday.

"I think we're in for some big surprises," participating scientist Faith Vilas said in a teleconference with reporters.

"This is raw scientific exploration and the suspense is building by the day," said Alan Stern, associated administrator for NASA's science Mission directorate, in a statement.

MESSENGER will measure the mineral and chemical composition of Mercury's surface, study its atmosphere and magnetosphere and collect data about the magnetic tail that sweeps behind it.

The spacecraft will fly as low as 124 miles (200 kilometers) above Mercury's cratered, rocky surface, and will use the planet's gravitational pull, in this flyover and two others planned this year and next, to position itself to enter the planet's orbit.

MESSENGER is scheduled to fly over Mercury again in October 2008 and September 2009, then return for a final sweep in 2011 when it will enter Mercury's orbit for a year-long study of the planet.

The spacecraft has already flown once past Earth and twice past Venus since its August 2004 launch. It will have travelled 7.8 billion kilometers (4.9 billion miles) when it completes its six and a half year odyssey.

The historic flyby Monday will be the first since the Mariner 10's March 1975 visit, when that spacecraft conducted three flights over the planet closest to the Sun. Mariner surveyed only one hemisphere of Mercury, using weaker observational tools.