February 16, 2021
Originally published July 29, 2011
images from Lunar Reconnaissance Orbiter Featured Image (NASA/GSFC/Arizona State University)
Sitting on the northeast rim of the Crisium Basin is Eimmart, an old degraded crater with a bright crater, Eimmart A, just touching its rim. A new LRO image release shows flows extending down slope from the sharp rimcrest of "A". These flows presumably are impact melt that originally started where ejected melt splashed onto the rim, ponded a little and then flowed downhill. But these flows have been beheaded - their starting points are missing. Presumably the original starting points have slid down into the floor of Eimmart A - in fact, hairline faults concentric to the rim are visible showing where future rim collapses may occur, truncating more of these melt flows. EImmart A is visible from Earth in backyard telescopes. Look for it in a few days when illumination returns to the eastern limb, and imagine what it was like when molten red impact melt flowed down the rim.
I remember that one of the lunar meteorites has an unusual composition that matched a unique chemical anomaly at Eimmart. If so, we may have a piece of the Moon ejected during the formation of Eimmart A. But I can't find which meteorite it was - does any one know?
Rükl plate 27
Yesterday's LPOD: Big Guns
Tomorrow's LPOD: Endless Moons