Boulders on an otherwise smooth floor are seen on the Mare Tranquillitatis pit crater on the surface of the Moon in this NASA image taken by the NASA's Lunar Reconnaissance Orbiter and released September 14, 2010. When the Sun is well overhead, the floor of the Mare Tranquillitatis pit is illuminated. Scientists estimate the depth to be a bit over 100 meters. REUTERS
Boulders on an otherwise smooth floor are seen on the Mare Tranquillitatis pit crater on the surface of the Moon in this NASA image taken by the NASA's Lunar Reconnaissance Orbiter and released September 14, 2010. When the Sun is well overhead, the floor of the Mare Tranquillitatis pit is illuminated. Scientists estimate the depth to be a bit over 100 meters. REUTERS