MESSENGER image of planet Mercury (left)
September 29, 2009
Image Mission Elapsed Time (MET):
Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
7 (748 nanometers)
Mercury's diameter is 4880 km (3030 mi.)
Dawn image of asteroid Vesta (right)
July 18, 2011
Dawn Framing Camera
, clear filter
Vesta's diameter is about 530 km (329 mi.)
In March 2011, MESSENGER became the first spacecraft to orbit the planet Mercury. In July of the same year, the Dawn
spacecraft became the first to orbit a main-belt asteroid, Vesta. Both MESSENGER and Dawn are missions in the Discovery program
, NASA's lowest-cost category of planetary mission.
The image above shows Mercury
on the left, and Vesta
on the right. Both surfaces are marked by impact craters, but the most immediately noticeable difference is that Vesta has a much more irregular shape. This is a consequence of Mercury's far larger gravity, which has squeezed the planet into a sphere. Vesta's weak gravity is less able to overcome the strength of the rocks. Mercury's mass is about 1300 times greater than that of Vesta.
The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation
are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury?
section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MDIS is scheduled to acquire more than 75,000 images in support of MESSENGER's science goals.
Dawn Vesta image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
MESSENGER Mercury image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
For information regarding the use of MESSENGER images, see the image use policy.