Thursday, November 8, 2012

Ghost crater in Mare Imbrium

A high reflectance near-buried ghost crater rim curves through a flat portion of mare basalt in Mare Imbrium. The line is elevated relative to the basalt and is populated with bright boulders. A 986 meter-wide field of view from LROC Narrow Angle Camera (NAC) M1098979692LE, LRO orbit 14305, August 7, 2012; resolution in original 1.7 meters [NASA/GSFC/Arizona State University].
Dew Enns
LROC News System

Today's Featured Image is a portion of a larger structure - a ghost crater!

Last week we explained how ghost craters are formed - basalt fills in and covers an older crater. The curved structure above is made up of high reflectance boulders on a ridge, hinting at the 5 km crater underneath. Ghost craters aren't just cool to look at though, they also help answer some questions about the lunar surface!

We know that the maria cover only about 17% of the Moon's surface, but how deep are they really? One way to estimate their depth is to catalog ghost craters that have been covered by mare basalt.

Context for the LROC Featured Image, released November 7, 2012 (64m resolution from LROC QuickMap). The ghost crater is located at 45.67° N, 338.89°E. Nearby (Laplace F) crater has a similar diameter to the ghost crater, implying that they are both excavated similar depths of material [NASA/GSFC/Arizona State University].
Impact craters have consistent depth:diameter ratios that we can model. If we measure the diameters of a ghost crater, we can estimate its depth, and we can then infer a minimum thickness of much basalt filling in the crater. Cataloging craters throughout the maria can inform us of the regional variation in basalt thickness.
Explore more of Mare Imbrium in the full LROC NAC, HERE.

Related Posts:
Ghost Crater in Southern Mare Crisium!
Balcony Over Plato
Archimedes - Mare Flooded Crater!

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