This NAC image from MESSENGER’s second Mercury flyby shows a crater with a
set of light-colored rays radiating outward from it. Such rays are formed
when an impact excavates material from below the surface and throws it
outward from the crater. These bright rays, consisting both of ejecta and
the secondary craters that form when the ejected material re-impacts the
surface, slowly begin to fade as they are exposed to the harsh space
environment. Mercury and other airless planetary bodies are constantly
being bombarded with micrometeorites and energetic ions, an effect known
as space weathering. Craters with bright rays are thought to be relatively
young because the rays are still visible, suggesting that they have had
less exposure to weathering processes. The crater in the center of this
image has rays that have already begun to fade, implying that it is older
than some other rayed craters on Mercury’s surface. Images of younger
craters with much brighter and more striking rays have been previously
released (see PIA11355).
Date Acquired: October 6, 2008
Image Mission Elapsed Time (MET): 131771863
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 240 meters/pixel (0.15 miles/pixel)
Scale: Image is approximately 240 kilometers (150 miles) wide
Spacecraft Altitude: 9,500 kilometers (5,900 miles)
These images are from MESSENGER, a NASA Discovery mission to conduct the
first orbital study of the innermost planet, Mercury. For information
regarding the use of images, see the MESSENGER image use policy.