Of ghosts and graveyards

Innumerable impact craters have formed throughout the Moon’s 4.6-billion-year history. The formation of subsequent craters and basins obliterated many previously existing impact craters, while lava flows surrounded, flooded or completely buried others. Eroded craters are shallow structures with rounded rims and are morphologically less dramatic than those that lava flows affect. Mare lavas breach crater rims, fill many large craters, cover ejecta deposits, nearly bury some craters, and totally erase others from the geological record.

One of the best places to observe the various stages of lava inundation is Unlike typical maria, this 700-km-wide expanse isn’t surrounded by rim remnants and lacks the gravitational anomalies found in other basins. The only hint that this particular mare fills an impact basin is that its centre is roughly 400 metres deeper than its edges. Nubium probably was an ancient basin that exists now only as a shallow pond of lava. This thin veneer of basalt is what makes it an ideal crater graveyard, with all the stages of crater/ lava interaction on display.