- Moon's radius has shrunk by 45 metres in the past 400 million years, study finds
- Lunar Reconnaissance Orbiter Camera images were used for analysis over 17 years
- Moon continues shrinking at 6-11 cm per million years, slower than Earth's plate movement
Moon, earth's only natural satellite, is contracting and scientists now know how fast the process is happening. In a study published in The Planetary Science Journal on October 14, says moon's radius has shrunk by 148 feet (45 metres) in the past 400 million years. The study was led by Thomas R Watters, scientist emeritus in the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum and used observations from the Lunar Reconnaissance Orbiter Camera (LROC).
Researchers analysed millions of images captured by LROC over a period of 17 years to understand the moon's structure as it continues to cool.
Going by the current rate of decrease, the study concluded that the moon will keep shrinking 6-11 centimetres per million years. This is much less than the average rate that Earth's plates move, about 1.5 centimetres per year - about the same rate fingernails grow - driven by heat loss from Earth's interior.
Though the moon has been shrinking for millions of years, scientists had earlier said that it will not shrink out of the view.
Another area highlighted by the study titled 'Thrust Faulting and the Late-Stage Contraction of the Moon' is the wrinkling and cracking of the moon's outer crust that form small cliffs called lobate scarps.
This shrinking causes moonquakes along thousands of small faults across the lunar surface, which agencies like NASA must account for while planning future missions like Artemis. They also spotted more than 10,000 young faults across the lunar surface.
The reason for concern is that unlike Earth, the cooling and shrinking can generate slips and faults anywhere on the lunar surface, said the study. On Earth, about 90 per cent of all the seismic activity occurs near the boundaries between lithospheric plates. But the moon is a single-plate body with faults that act like an unbroken shell.
This means moonquakes can occur anywhere on the lunar surface.
Scientists believe that the moon had a violent birth. When one large object crashed into Earth billions of years ago, large hot debris were thrown into the space that coalesced into the moon.
