NASA's Messenger spacecraft has returned pictures of previously unseen areas of Mercury's surface, along with hundreds of new photos and measurements of the planet's surface, atmosphere and magnetic field.
Messenger flew by Mercury on October 6. It completed a critical gravity assist to keep it on course to orbit Mercury in 2011 and got a look at 30 percent of Mercury's surface which had never before been seen by a spacecraft.
Cameras took more than 1,200 pictures of the surface, while topography beneath the spacecraft was profiled with a laser altimeter. The comparison of magnetosphere observations from the spacecraft's first flyby in January with data from the probe's second pass has provided key new insights into Mercury's magnetic field.
"The previous flybys by Messenger and Mariner 10 provided data only about Mercury's eastern hemisphere," explains Brian Anderson of the Johns Hopkins University Applied Physics Laboratory. "The most recent flyby gave us our first measurements on Mercury's western hemisphere, and with them we discovered that the planet's magnetic field is highly symmetric."
Many new features were revealed during the third flyby, including a region with a bright area surrounding an irregular depression, suspected to be volcanic in origin. Other images revealed a double-ring impact basin approximately 180 miles across, similar to a feature scientists call the Raditladi basin, which was viewed during the probe's first flyby of Mercury in January 2008.
"Now that Messenger's cameras have imaged more than 80 percent of Mercury, it is clear that, unlike the moon and Mars, Mercury's surface is more homogeneously ancient and heavily cratered, with large extents of younger volcanic plains lying within and between giant impact basins," said co-investigator Mark Robinson of Arizona State University.
There's more information here.