|This LROC Narrow Angle Camera (NAC) frame exposes two seemingly different lithologies; one dark with several craters, and one light with few. What are we observing? LROC NAC observation M1113062041RE, spacecraft orbit 16278, January 17, 2013; 70 cm resolution of a field of view 700 meters across [NASA/GSFC/Arizona State University].|
LROC News System
Today's Featured Image shows a very interesting dichotomy on the Moon. One half of the image displays a dark cratered surface, while the other half is lighter in tone with less craters and a different texture. What could cause the difference in brightness, cratering, and texture? What sort of geologic contact are we observing?
Perhaps the bright material is younger, and as a result has fewer craters. Young lunar craters and their ejecta have a higher reflectance than older ones, and their ejecta blankets are only lightly cratered. The darker material could be older lunar terrain that the ejecta has overlain, and we are looking at the contact between these two surface types.
We could also be observing the interior of a crater. The texture of the brighter material is consistent with textures we see on sloped surfaces such as a crater wall. The difference in crater density can be explained as a result of the sloped wall of the crater. The darker half might then be the impact melt at the bottom of the crater floor.
Another hypothesis might be that we are observing the geologic contact between mare basalts and the lunar highlands. The mare are darker than the highlands but should have fewer craters. But that is not what we observe, unless the lighter material is on a slope (such as in our crater interior hypothesis). Which one of these hypotheses is correct? Let's look at a contextual view from the LROC WAC for help.
|Context LROC Wide Angle Camera (WAC) 100 km-wide field of view designating the location shown at high resolution in the LROC Featured Image, released February 12, 2013. Northeast Mare Ingenii, just beyond the nearly buried rim of Thompson crater on the lunar far side. The contact coordinates are 31.069°S, 168.657°E. This Image width is 100 km [NASA/GSFC/Arizona State University].|
|Apollo 15, beginning its 14th orbit, 1971, reemerging into day high to the northwest, delivered this beautiful oblique context photograph of the area of interest, Thompson crater and the surrounding quadrant of northeast Mare Ingenii (the contact is near center in this full resolution inset from AS15-87-11724) in the stark relief of the lengthening shadows of late afternoon [NASA/JSC].|
|The full frame of the Apollo 15 frame of Mare Ingenii taken from a point nearly antipodal to the expedition's landing site at Hadley Rille. Catch the high-resolution reproduction at the Apollo Lunar Surface Journal HERE [NASA/JSC/ALSJ].|
Approach to Taurus Littrow Valley
Follow the highlands-mare boundary in Tsiolkovskiy!
Mare Moscoviense Constellation Site