Ghost craters on the Moon!

Here is a ghost crater, can you see it?

Ghost crater Lambert R, captured from orbit by NASA’s Apollo 17. Source: NASA

A ghost crater is a crater buried in lava, with only the crater rim visible. How do they form? Say a regular crater forms by an asteroid/meteor impact at some point. After that, during the time of active volcanism on the Moon, lava eruptions in the area may fill the crater to the brim, leaving behind just the rim. Many such ghost craters have been spotted on the Moon. My favorite is this one where the crater is fully submerged in lava, but the bright ejecta from the impact is still visible!

A 650-700 m ghost crater with visible ejecta. Credit: NASA Lunar Reconnaissance Orbiter (LRO)

Long-time Moon Monday readers will get reminded of the previously covered Lunar Kipuka, which is a similar feature. One of the ways scientists know these ghost craters really are craters is by imaging them from orbit at low-sun angles. Their rim, if it is a crater, casts a long shadow in such cases and makes its nature apparent.

More complex ghost craters have been observed on Mercury from past missions, decorated with graben and ridges! Fascinating stuff.

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