August 18, 2013
Image Mission Elapsed Time (MET):
Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
2 (700 nanometers)
Scale: Prokofiev crater
(outlined in cyan in the upper left) has a diameter of 112 km (70 miles)
Polar stereographic about the north pole, with 180° E to the top
Outline of radar-bright regions
, acquired by the Arecibo Observatory (Harmon et al, 2011, Icarus, 211, 37-50)
This WAC image reveals the permanently shadowed surface within Prokofiev crater, the largest crater in Mercury's north polar region
to host radar-bright material. MESSENGER has found evidence
that the radar-bright material is water ice frozen in the cold, dark shadows of this crater, but this image reveals the surface at visible wavelengths for the first time. In the upper left, the full crater is shown outlined in cyan; the region in the pink box is shown in more detail in the image on the right. The WAC image here shows that the region that is radar-bright (outlined in yellow) has a higher reflectance in the image, interpreted to be due to water ice on the surface! The radar-bright surface is also covered with many craters. Since ejecta from the craters don't hide the higher reflectance surface, it suggests that the ice in this crater was emplaced on the surface after the craters were formed. Read more about the recently published study using this image and others in this news story
This image was acquired as part of MDIS's campaign to image within regions of permanent shadow in ice-bearing polar craters. Imaging with the WAC broadband clear filter, which has a bandwidth of 600 nanometers and is used for calibration imaging of stars, has the potential to reveal details of shadowed surfaces that are weakly illuminated by scattered sunlight. A variety of image exposure times and viewing conditions are employed to maximize the opportunity to resolve surface features of areas in permanent shadow.
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. In the mission's more than three years of orbital operations, MESSENGER has acquired over 250,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015.
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.