The MESSENGER spacecraft in orbit around the planet Mercury has been lowering its altitude slowly and as it gets closer to the surface of the planet it stands to reason the pictures should show more detail.
Judging from this image that is exactly what is happening. As MESSENGER enters its last year, the observations will become much more detailed. On 30 April the spacecraft altitide was 199 km (127 miles) and MESSENGER is supposed to get even lower, by about half. There is a orbit-correction manuever set for 17 June.
Those white spots along the crater rim are not washed out areas, they are hallows, depressions with bright centers. Apparently they only occur or are only noticed to occur on the sunlit areas.
Here’s the MESSENGER caption for the image:
As MESSENGER passes progressively closer to Mercury, we see ever more resolved features in the images the spacecraft returns. Here, at a pixel scale of 9 meters, we see the eastern portion of an unnamed crater 13 km (8 mi.) in diameter. The wall of the crater is replete with smaller, superposed craters, some of which appear elongate possibly because they impacted on the larger crater’s inclined wall. Interestingly, there are bright spots on the sunlight portion of this crater’s wall — which is where we might expect hollows to form.
This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury’s surface at resolutions much higher than the 200-meter/pixel morphology base map. It is not possible to cover all of Mercury’s surface at this high resolution, but typically several areas of high scientific interest are imaged in this mode each week.
Date acquired: March 3, 2014
Image Mission Elapsed Time (MET): 36136338
Image ID: 5862963
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 56.3°
Center Longitude: 301.6° E
Resolution: 9 meters/pixel
Scale: The field of view in this image is 11 km (7 mi.) across
Incidence Angle: 59.3°
Emission Angle: 43.0°
Phase Angle: 102.3°
North is to the right in this scene.
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. MESSENGER acquired over 150,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015.