A high reflectance line curves through a flat portion of mare basalt. The line is elevated relative to the basalt and is populated with bright boulders. LROC NAC 1098979692LE, image width is 1700 [NASA/GSFC/Arizona State University].
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!
Context image for today's Featured Image. The ghost crater is located at 46.67° N338.89°E. A nearby crater has a similar diameter to the ghost crater, implying that they are both excavated similar depths of material. Image width is 70 km [NASA/GSFC/Arizona State University].
We know that the maria cover ~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. 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.