LROC: A small crater's disappearing floor

Floor of unnamed crater inside the western rim of the Humboldt 'walled plain.' LROC Narrow Angle Camera (NAC) observation M113440414L, LRO Orbit 1851, November 21, 2009; resolution 51 cm per pixel, incidence angle 54° from 46.93 km. Field of view 296 meters across. View the wider full size LROC Featured Image HERE [NASA/GSFC/Arizona State University].

Hiroyuki Sato
LROC News System

Humboldt crater is a large (207 kilometers) floor-fractured crater on the eastern limb, as seen from the Earth, just before the 80° east meridian (in the Zone of Libration), about 760 km south of Mare Smythii. The edges of its fractured-floor are partially covered by dark mantle deposits, which are suspected to be pyroclastic in origin.

Today's Featured Image is the bottom of an unnamed 5.7 km crater near the western edge of the Humboldt crater floor (26.25°S, 78.41°E). The boomerang-shaped flat area in the center of this image is the original floor, surrounded by continuous slopes from the crater rim.

LROC Wide Angle Camera 100 m Global Mosaic fixed to an initial LOLA laser altimetry-based digital terrain model in a scene built up through the NASA ILIADS platform, where a variety of lunar probe data bases from multiple NASA centers are made available to the public.The asterisk marks the location of the field of view within the LROC Featured Image and the yellow rectangle indicates the LROC NAC image footprint from which it was taken [NASA/ILIADS].

The initial shape just after the impact event is generally thought to be a symmetric bowl-shape, with mass wasting gradually modifying the crater cavity. Especially for the small craters on the Moon, bowl-shaped cavities are transformed by this process into inverted cone shapes. This unnamed crater in Humboldt may be undergoing such a process now to become a complete cone shape at some point in the future. If so, we are fortunate to observe its original floor before complete burial obscures it from view.

A second, more recent LROC WAC monochrome (604 nm) mosaic of the western interior of the Humboldt plain, for comparison with the afternoon illumination further up it shows the unnamed crater in a field of view approximately 45 kilometers wide under early morning illumination. LROC WAC observations M161801162C, M161794365CE & M161787569CE in LRO orbits 8976-8978, June 4, 2011; average resolution 66.75 meters, incidence angle 70.8° from 47.45 kilometers [NASA/GSFC/Arizona State University].

LROC WAC monochrome mosaic around Humboldt, with a false-color overlay representing the LROC photography-based digital terrain model (DTM), at (default) 30% opacity and 250 meter resolution, as viewed through the LROC QuickMap web-based application. The unnamed crater and its surroundings are seen in the wider context of Greater Humboldt on the western edge of the larger crater floor, with its high walls and radial fractures. View the full size original LROC WAC context image HERE [NASA/GSFC/Arizona State University].

Explore the last portion of this unnamed crater floor in the full NAC frame yourself!

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