LROC: Melt pit on the floor of Louville D

Fractured impact melt with a probable impact melt pit inside the crater Louville D. LROC Narrow Angle Camera (NAC) observation M170897609R, LRO orbit 10319, September 17, 2011; resolution 0.5 meters from 45.36 km [NASA/GSFC/Arizona State University].

Sarah Braden

LROC News System

Louville D is a young crater, 6.89 km in diameter, located in northeastern Mare Procellarum (46.85°N, 52.13°W), near Sinus Roris.

The Featured Image shows a group of fractures and one possible pit (center of image) within the impact melt at the bottom of Louville D.

How do we determine what is a possible impact melt pit and what is a shadow from a boulder? The most important source of information on this is multiple images at different viewing angles.

For instance, in one image the Sun is low in the sky and many shadows are cast due to crater rims, boulders, and fractures. In a different image with the Sun high in the sky there are almost no shadows. In this high-sun case, pits are extremely visible as dark areas that reflect very little light back into space. High-sun images result in an unambiguous identification of a lunar pit. But what happens when we do not have a high-sun image of a potential pit?

A smaller-scale image from LROC NAC M170897609R show the floor of Louville D in context with the contact zone with the 6.89 km-wide crater's walls [NASA/GSFC/Arizona State University].

While looking at an image with many shadows, it may be unclear if an area is a shadow or an actual pit in the impact melt. Most of the time you can see the boulders well enough to match a shadow to the corresponding boulder, but sometimes the boulders or the topography can be hard to see. A handy trick is to look at the amount of light in the dark area. In most cases, there is enough light in shadows for LROC to detect. This light is reflected into the shadows by surrounding objects. However, less light can reach the inside of a pit, and LROC will detect overall less light in pits.

LROC WAC context image of Louville D with Rima Sharp to the east. The full-size Wide Angle Camera mosaic field of view 100 km [NASA/GSFC/Arizona State University].

Explore a closer look at this possible impact melt pit and the floor of Louville D in another full resolution NAC frame (M142604009R), HERE.

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A view of Rima Sharp and Louville D and Louville DA from the north from a Planetary Camera image captured by Japan's lunar orbiter SELENE-1 (Kaguya) [JAXA/SELENE]

There's a lot more natural history engraved on this area of the lunar surface than meets the casual observation, shown by the USGS, reduced from USGS Rumker I805 [USGS].