NASA GSFC - 2010 March 04
Shortly after the Moon formed, an asteroid smacked into its southern hemisphere and gouged out a truly enormous crater, the South Pole-Aitken basin, almost 1,500 miles across and more than five miles deep.
"This is the biggest, deepest crater on the Moon -- an abyss that could engulf the United States from the East Coast through Texas," said Noah Petro of NASA’s Goddard Space Flight Center in Greenbelt, Md. The impact punched into the layers of the lunar crust, scattering that material across the Moon and into space. The tremendous heat of the impact also melted part of the floor of the crater, turning it into a sea of molten rock.
That was just an opening shot. Asteroid bombardment over billions of years has left the lunar surface pockmarked with craters of all sizes, and covered with solidified lava, rubble, and dust. Glimpses of the original surface, or crust, are rare, and views into the deep crust are rarer still.
Fortunately, a crater on the edge of the South Pole-Aitken basin may provide just such a view. Called the Apollo Basin and formed by the later impact of a smaller asteroid, it still measures a respectable 300 miles across.
Image 1: This is elevation map covering the eastern portion of South Pole-Aitken basin, including the Apollo Basin,
made using data from Japan’s Kaguya spacecraft. The false colors indicate height; red represents highlands, and
blue represents the lowest areas. Dashed circles mark the location of the main and inner ring of Apollo. The dashed
line marks the location of the topographic profile illustrated in the Image 2 below. (JAXA/NASA)
Image 2: This is a graph of the elevation (in meters) from the rim of the South Pole-Aitken basin through the Apollo basin
made using data from Japan’s Kaguya spacecraft. The endpoints (A and A’) are marked in Image 1 above. (JAXA/NASA)