The Moon has been stretched within the past 50 million years — a surprising and relatively recent sign of extensional tectonics for a body that has been around for 4.5 billion years.

Credit: ARIZONA STATE UNIV./GSFC/NASA

Using a camera on NASA's Lunar Reconnaissance Orbiter, Thomas Watters of the Smithsonian Institution in Washington DC and his colleagues spotted graben — long, narrow blocks of rock that drop down and form trenches as the Moon's crust is stretched. Some of the graben are as shallow as one metre, suggesting that, in geological terms, they are fresh.

The authors suggest that their findings are inconsistent with models that predict that the primordial Moon was completely molten and would have contracted so much that local extensional pressures would have been quashed. Instead, the graben may reflect an environment of weaker contractions that resulted from the early Moon having only a molten exterior.

Nature Geosci. http://dx.doi.org/10.1038/ngeo1387 (2012)