Credit: MESSENGER, NASA, JHU APL, CIW
Explanation: Why are many large craters on Mercury relatively smooth inside? Recent images from the robotic MESSENGER spacecraft that flew by Mercury in October 2008 show previously uncharted regions of Mercury that have large craters with an internal smoothness similar to the maria on Earth's own Moon. Therefore, like our Moon's maria, these craters on Mercury are thought to have been flooded by lava floes that are old but not as old as the surrounding more highly cratered surface. The above image mosaic of the western limb of Mercury was created by MESSENGER as it approached the Solar System's innermost planet last October. Old and heavily textured terrain runs across much of the image bottom, while across the middle left lies comparatively smooth impact basins where small craters may appear similar at first to protruding hills. MESSENGER will buzz past Mercury again next year before entering orbit in 2011.
MESSENGER Returns to Mercury
MESSENGER is the first mission sent to orbit the planet closest to the sun. On Oct. 6, 2008, at roughly 4:40 a.m. ET, MESSENGER flew by Mercury for the second time in 2008. During the encounter, the probe swung just 125 miles (200 kilometers) above the cratered surface of Mercury, snapping hundreds of pictures and collecting a variety of other data from the planet as it gains a critical gravity assist that keeps the probe on track to become the first spacecraft ever to orbit the innermost planet beginning in March 2011.
FOR MORE ON MESSENGER go to: http://www.nasa.gov/mission_pages/messenger/main/index.html
HIGHEST RESOLUTION PHOTO OF MERCURY 90 MINUTES AFTER MESSENGER FLYBY AT A DISTANCE OF 27,000 KM
(NEXT AND FINAL OF THREE FLYBYS IS TO OCCUR 0N 2009 SEPTEMBER 29 - ORBITAL INSERTION IN MARCH 2011)