Featured Image - (06/03/2008)
Lambert R: Buried by lava
The Apollo 15 Metric camera captured the dynamic interaction between mare volcanism and lunar craters in southern Mare Imbrium. The crater with the deeply shadowed interior is Lambert, an Erastosthenian-aged feature with a diameter of 30 km. The unusual 55 km-wide circular feature just south of Lambert is known as Lambert R.
What is Lambert R?
Geologist interpret mare wrinkle ridges as structural deformation features caused by the subsidence and cooling of mare lavas, but sometimes similar ridges are caused by the interaction between flowing mare lavas and the preexisting topography. Lunar scientists think that Lambert R is actually an impact crater that was flooded by massive lava flows. As the lava buried the crater, it cooled, shrank, and molded to the shape of the crater rim, resulting in the circular ridges. On the lunar surface, we see both lunar craters and large impact basins that have been buried by lavas, but are still detectable because of these circular ridge patterns. While buried lunar features don't sound very useful, it turns out that they are! The only reason that lunar scientists know the location of the inner ring of the giant Imbrium impact basin, for example, is because we can see its circular ridge features in Mare Imbrium. Similarly, Lambert R has a diameter of 55 km. By finding a similarly-sized crater that is not buried and measuring its rim height relative to its surroundings, we can estimate the thickness of the regional flood lavas that buried Lambert R, one of several techniques that lunar scientists can use to reconstruct lunar stratigraphy. The new data returned by the Lunar Reconnaissance Orbiter and other ongoing and planned lunar missions will let us more accurately map similar lunar features in underexplored areas all over the Moon's surface as we prepare for the next generation of human lunar exploration.
Apollo metric image showing Lambert and the buried Lambert R craters in southern Mare Imbrium. (Apollo Image AS15-M-1010 [NASA/JSC/Arizona State University])