Known as the Mercury Space Environment Geochemistry and Ranging mission, or Messenger, the spacecraft will carry seven miniaturized instruments, said Daniel Baker, director of CU-Boulder's Laboratory for Atmospheric and Space Physics. As part of NASA's new Discovery Program missions, Messenger will be the first spacecraft to visit Mercury in more than 30 years.

The only previous mission to Mercury was NASA's Mariner 10 spacecraft, which flew by the planet three times in 1974 and 1975.

The CU-Boulder instrument, the Atmospheric and Surface Composition Spectrometer, will be built under the direction of principal investigator and LASP Research Associate William McClintock and Baker to study the atmosphere, magnetosphere (the region surrounding Mercury that is permeated by its magnetic field) and surface of the planet.

The CU-Boulder instrument is expected to cost about $7 million to design, build and test, McClintock said. The entire Messenger mission is expected to cost about $286 million.

Baker is particularly interested in understanding Mercury's magnetic field and particle environment and to compare and contrast them with Earth's magnetosphere. Although Earth's magnetic field is thought to be generated by molten liquid swirling in the outer portions of its core, scientists believe Mercury's core should have solidified long ago because of the planet's size - less than half the diameter of Earth.

One big question is how such a strong magnetic field persists today, the CU-Boulder researchers said.

The CU spectrometer also will measure the tenuous atmosphere surrounding the planet and signatures of the minerals present on the surface. This information will help scientists to determine the composition of the surface rocks and to understand how the constituents in the atmosphere and magnetosphere are related to each other, McClintock said.

The chief mission scientist of Messenger is Sean Solomon of the Carnegie Institute in Washington, D.C. The project will be managed by John Hopkins University's Applied Physics Laboratory.

Messenger is slated to fly by Mercury twice in 2008, then enter a one-year orbit to map the entire planet and study the composition of its atmosphere and the behavior of its magnetosphere. Both graduate students and undergraduates at CU-Boulder will help to analyze the data that is returned to Earth, said Baker.