U.S. spacecraft poised to fly past Mercury next week

By Will Dunham

WASHINGTON (Reuters) - A NASA spacecraft will whiz over Mercury's crater-scarred surface next Monday, getting a look at the third of the planet closest to the sun that has never been seen close-up before.

It is a return engagement for the car-sized MESSENGER probe, which darted past Mercury on January 14 during its ongoing mission to explore the small and rocky sun-baked world.

MESSENGER is due to fly about 124 miles above Mercury's surface at nearly 15,000 mph .

The only previous times Mercury was visited by a spacecraft was in 1974 and 1975 when NASA's Mariner 10 flew past it three times and mapped about 45 percent of its surface. January's fly-by by MESSENGER covered another 20 percent of the surface, the U.S. space agency said.

Next week's fly-by will cover about 30 percent more, on the opposite side of the planet from the one seen in January.

"That represents an area bigger than the land area of South America that will be seen for the first time by our spacecraft," Sean Solomon of Carnegie Institution of Washington, the mission's lead investigator, told reporters.

The probe is due to take 1,200 images during the encounter with Mercury, which is two-thirds closer to the sun than Earth.

Data from the January fly-by showed that volcanic activity played a key role in forging Mercury's surface and that the planet has been shrinking more than expected over time.