Analyses of data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft’s second flyby of Mercury in October 2008 show that the planet’s atmosphere, magnetosphere, and geological past are all characterized by much greater levels of activity than scientists first suspected.

On October 6, 2008, the probe flew by Mercury for the second time, capturing more than 1,200 high-resolution and color images of the planet unveiling another 30 percent of Mercury’s surface that had never before been seen by spacecraft and gathering essential data for planning the remainder of the mission.

“MESSENGER’s second Mercury flyby provided a number of new findings,” says MESSENGER Principal Investigator Sean Solomon at the Carnegie Institution of Washington. “One of the biggest surprises was how strongly the planet’s magnetospheric dynamics changed from what we saw during the first Mercury flyby in January 2008. Another was the discovery of a large and unusually well preserved impact basin that was the focus for concentrated volcanic and deformational activity. The first detection of magnesium in Mercury’s exosphere and neutral tail provides confirmation that magnesium is an important constituent of Mercury’s surface materials. And our nearly global imaging coverage of the surface after this flyby has given us fresh insight into how the planet's crust was formed.”

These findings are reported in four papers published in the May 1 issue of Science magazine. See the MESSENGER site for more

Credit: Image produced by NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS.