MESSENGER Spacecraft Reveals New Information About Mercury

The first spacecraft designed by NASA to orbit Mercury is giving scientists a new perspective on the planet's atmosphere and evolution.

Launched in August 2004, the Mercury Surface, Space Environment, Geochemistry and Ranging spacecraft, known as MESSENGER, conducted a third and final flyby of Mercury in September 2009. The probe completed a critical maneuver using the planet's gravity to remain on course to enter into orbit around Mercury next year.

Data from the final flyby has revealed the first observations of ion emissions in Mercury's exosphere, or thin atmosphere; new information about the planet's magnetic substorms; and evidence of younger volcanic activity than previously recorded. The results are reported in three papers published online in the July 15 edition of Science Express.

The distribution of individual chemical elements that the spacecraft saw in Mercury’s exosphere varied around the planet. Detailed altitude profiles of those elements in the exosphere over the north and south poles of the planet were also measured for the first time.

"These profiles showed considerable variability among the sodium, calcium, and magnesium distributions, indicating that several processes are at work and that a given process may affect each element quite differently," said Ron Vervack, lead author of one of the papers and the spacecraft's participating scientist at the Johns Hopkins University Applied Physics Laboratory , in Laurel, Md.

In addition to flying by Mercury, the spacecraft flew past Earth in August 2005 and Venus in October 2006 and June 2007. Approximately 98 percent of Mercury's surface has been imaged by NASA spacecraft. After this spacecraft goes into orbit around Mercury for a yearlong study of the planet, it will observe the polar regions, which are the only unobserved areas of the planet.

The spacecraft was designed and built by APL. The mission is managed and operated by APL for NASA's Science Mission Directorate in Washington.