Tuesday, May 29, 2012

LROC: Balcony over Plato

A distinctive rock outcrop attracts attention along the north rim of nearside landmark crater Plato (51.6°N; 9.4°W). Illumination from the southeast, downslope toward bottom of a field of view approximately 325 meters across; LROC Narrow Angle Camera (NAC) observation M168257774L, LRO orbit 9930, August 17, 2011. Resolution 0.44 meters from 33.43 kilometers [NASA/GSFC/Arizona State University].
James Ashley

Much of the Plato crater walls exhibit relatively smooth slopes. This small area, however, displays an eye-catching pattern of rocks protruding from the surrounding surface. 

The outcrop represents a locally resistant bedrock unit on the steeply sloping walls. Note how the rock protrusions appear to be aligned in horizontal rows. Does this mean that the rocks are layered? 

Compare with other images of clearly layered units in crater walls.

This NAC context image shows a relatively isolated region of resistant rock surrounded by the smooth sloping walls of Plato crater [NASA/GSFC/Arizona State University].
From the context images above and below, we see that the rocks have likely been sculpted by slumping in the crater walls, which also accounts for wall smoothness in the area surrounding the outcrop. Plato is a 109-km diameter crater that is isolated from Mare Imbrium by these walls. Its floor is filled with lava deposits like those of Imbrium and other mares, but there is no direct connection to other mare deposits. Lava must have entered Plato through fissures in its floor, and filled the crater to the level we see today. What a fine vantage point this balcony of natural benches would have provided to the fortunate astronaut were it possible to travel through time to watch the floor of Plato flood with orange-red lava more than three and half billion years ago!

This LROC Wide Angle Camera (WAC) monochrome (643nm) view of the north wall of Plato shows the outcrop hundreds of meters over the mare inundated crater floor. Field of view is approximately 32 km across, resolution about 55 meters from 39 kilometers, February 4, 2010 [NASA/GSFC/Arizona State University].
On a good night, Plato can be seen clearly through a backyard telescope within the terrain between Mare Imbrium and Mare Frigoris.

Explore the full LROC Narrow Angle Camera frame HERE.

Other examples of rock outcrops exposed by impact craters on the Moon can be examined in the following Featured Image posts: Layering in Messier A, At the Top of the Avalanche, and Lava Flows Exposed in Bessel Crater.

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