Sky's Up - Fall 2015 - Page 16

Quadrant 46: — Images and text provided by Howard Eskildsen Lansberg to Mare Cognitum This region features broad expanses of basaltic lava plains interrupted by craters large and small, fresh or ruined. Mountain peaks punctuate the landscape here and there, and rocky rubble litters the upper right margin of this image. All tell stories, like the pages of a book, of triumph and disaster on the moon. Lansberg at the top of the image is well preserved with all the features of a large crater distinct, except for the absence of rays radiating from its rim. Simple craters such as Euclides, Eppinger, Kuiper and Darney dot the landscape as well. Of the four mentioned, only Euclides shows any hints of rays suggesting that the others are more than a billion years old, since space weathering tends to eliminate rays within a billion years. This is partly due to “gardening” from meteoroids impacting and from the effects of solar wind changing iron oxides into tiny flecks of iron known as nanophase iron, which gives the undisturbed lunar surface its characteristic color. Other unlabeled craters also show some rays, revealing their “youthful” Copernican age. Mountains also punctuate the surface as isolated peaks or as curious partial arcs, such as the Riphaeus Mountains. Look closely and you will find other curving ridges. They all hint at the primary cause of mountain building on the moon: crater-forming impacts. They were all at one time or another parts of crater rims, but were subsequently partially buried or eroded into their current forms. The burying is obviously from the lavas, also known as mare basalts that pave much of the visible surface in this image. But what could cause massive erosion and scouring such as seen at Fra Mauro, Bonpland and Parry? The region labeled Imbrium Ejecta is similar to the rough rubble 6VV