The moon is shrinking and shrivelling “like a wrinkled grape drying out to a raisin”, Nasa has said.
Scientists today said the moon is wrinkling as its interior cools, saying: “Just as a grape wrinkles as it shrinks down to a raisin, the moon gets wrinkles as it shrinks.”
The process is also causing “moonquakes” of up to 5.0 in magnitude, Nasa said in a statement.
“Unlike the flexible skin on a grape,” the release said, “the moon’s surface crust is brittle, so it breaks as the moon shrinks, forming ‘thrust faults’ where one section of crust is pushed up over a neighbouring part.”
Thomas Watters, senior scientist at the Center for Earth and Planetary Studies, said: “Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the moon continues to gradually cool and shrink.”
Mr Watters has been studying a new algorithm which has even prompted a review of past quakes on the moon.
In the ‘60s and ‘70s, astronauts placed instruments on the lunar surface during the Apollo 11, 12, 14, 15, and 16 missions. The Apollo 11 seismometer only worked for three weeks, but the four remaining instruments recorded 28 shallow moonquakes between 1969 to 1977.
Using the revised location estimates from the new algorithm, Mr Watters’ team found that eight of the 28 quakes were within 18.6 miles of the faults visible in lunar images.
Mr Watters said: “We think it’s very likely that these eight quakes were produced by faults slipping as stress built up when the lunar crust was compressed by global contraction and tidal forces, indicating that the Apollo seismometers recorded the shrinking moon and the moon is still tectonically active.”
The moon isn’t the only world in the solar system experiencing shrinkage with age.
Mercury has "enormous" thrust faults up to about 600 miles long and over a mile high. These are significantly larger relative to its size than those on the moon, Nasa said.