Astronomers have revealed the moon's recent geological activity -- they claim the Earth's natural satellite's crust is being stretched, forming minute valleys in a few small areas on the lunar surface.

A team, led by the Center for Earth and Planetary Studies at Smithsonian's National Air and Space Museum in Washington, says that this geologic activity occurred less than 50 million years ago, which is considered recent compared to the moon's age of more than 4.5 billion years.

Analysing images from NASA's Lunar Reconnaissance Orbiter, the planetary scientists found small, narrow trenches on moon, typically much longer than they are wide.

This indicates the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon's crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have been found across the lunar surface.

"We think the moon is in a general state of global contraction because of cooling of a still hot interior. The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart.

"This means the contractional forces shrinking the moon cannot be large, or the small graben might never form," said Thomas Watters, who led the team.

The weak contraction suggests that the moon, unlike the terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon's exterior initially melted forming an ocean of molten rock.

Based on the size of the scarps, it is estimated that the distance between the moon's centre and its surface shank by approximately 300 feet, NASA said in a release.
"This pulling apart tells us the moon is still active," said Richard Vondrak, LRO Project Scientist at NASA's Goddard Space Flight Center in Greenbelt.

The findings are to be published in an upcoming edition of the 'Nature Geoscience' journal.