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cientists are eagerly awaiting new images and observations when a MESSENGER spacecraft flies over Mercury in the first visit in almost 33 years to the mysterious small planet.

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 on 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," Alan Stern, associated administrator for NASA's science Mission directorate said.

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 200 kilometres 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 planets 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 kilometres when it completes its six and a half year odyssey.