A US space probe will fly over Mercury next week to photograph the solar system's smallest planet, in the second of three planned passes, NASA announced on Wednesday.

The spacecraft MESSENGER (MErcury Surface, Space ENvironment, GEochemistry and Ranging) will glide past the innermost planet on Monday at an altitude of 201 kilometers (125 miles) with its camera taking more than 1,200 images of the cratered surface.

Mercury is the closest of all the planets to the Sun, and because of the high-risks of its proximity -- the Sun's enormous gravitational pull, and massively high levels of radiation -- it is one of the most mysterious bodies in the solar system, even though it is relatively close to Earth.

"The results from MESSENGER's first fly-by of Mercury resolved debates that are more than 30 years old," said Sean Solomon, the mission's principal investigator from the Carnegie Institution of Washington.

"This second encounter will uncover even more information about the planet."

MESSENGER first flew past Mercury in January this year, and will make its final pass in September 2009. By that time it would have orbited the Sun 15 times and covered eight billion kilometers.

Next week's trip hopes to investigate the opposite side of the planet than the one seen on the first visit, said Louise Prockter, instrument scientist for the spacecraft's Mercury Dual Imaging System at the Johns Hopkins University Applied Physics Laboratory, in Laurel, Maryland.

Scientists and observers hope the probe will yield more answers to the physical processes that govern Mercury's atmosphere, along with more information about the charged particles located around the planet's dynamic magnetic field.

The craft is equipped with an altimeter to measure the planet's topography, which, for the first time, will allow scientists to correlate precise topography measurements with high-resolution images of the planet's surface.

The January visit showed scientists that volcanic eruptions produced many of Mercury's expansive plains, littered with meteor craters, and that its magnetic field appears to be actively generated in a molten iron core.

Before MESSENGER, the only other craft to visit Mercury was Mariner 10, which passed the planet three times in 1974 and 1975.