May 3, 2009
A Basin Full of Lava
image by John F M Maley, Herefordshire, UK
The 1160 km diameter ring defined by the arc of Apennine and Carpathian mountains is full of mare basalts. We don't know how thick the lavas are in the basin, but based on deductions from its gravity anomaly (or mascon) the best estimate is about 5 km. What we can see is that most of the subsequent impact craters larger than 5-10 km in diameter are in the outer third of the mare; the largest craters closest to the basin center are Timocharis (33 km) and Lambert (30 km). This is consistent with the center portion of the basin being the deepest, and the edges being most shallow - which is exactly what would be expected. The fact that there are no large craters near the middle implies that any that were created in the interval between basin formation and lava filling were completely covered over by the thick pile of lava. Fifty-five km wide Lambert R is an example of a crater that was nearly completely obliterated.
see image margin
Rükl plate 11 (and many more)
Yesterday's LPOD: Smaller And Smaller Rilles
Tomorrow's LPOD: La Voyage Dans La Lune