SPACE 14 January 2008 NASA MESSENGER due to make first pass by Mercury. Due to begin orbit in 2011

NASA launched the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission on 3 Aug 2004, and it is due to make the first of three flybys of Mercury on Jan 14. When it settles into the orbit of the planet closest to the Sun in 2011, it is expected to reveal the chemical composition of Mercury's surface, the geologic history, the nature of the magnetic field, the size and state of the core, the volatile inventory at the poles, and the nature of Mercury's exosphere and magnetosphere over a nominal orbital mission of one Earth year. The data will build on a surprise discovery in 2007.

Researchers working with high-precision planetary radars, including the Goldstone Solar System Radar of NASA's Jet Propulsion Laboratory in California, have discovered strong evidence that Mercury has a molten core, explaining a mystery left over from NASA's Mariner 10 mission in 1974 and 1975. Among its discoveries from three close passes was that Mercury had its own weak magnetic field - a factor associated with molten cores. But scientists at the time regarded the planet as too small to have a molten core.

MESSENGER flew by Earth one year after launch, and twice by Venus in 2007. Data collected during the Mercury flybys will be used to help plan the scientific campaign during the orbital phase.