Planetary scientists have discovered a series of ridges on the nearside of the Moon that might indicate new geological activity on the surface of our natural satellite. They think these are the results of a cataclysmic collision that happened long ago, on the other side of the Moon.
As reported in the journal Geology, the researchers discovered regions of exposed bedrock around and inside the lunar maria (seas), the darker regions we can see on the face of the Moon. The lunar surface is covered in regolith, a powdery soil made of ground-up rocks from the constant fall of tiny meteorites and the occasional larger object. Finding a bare area is certainly a hallmark of activity.
"Exposed blocks on the surface have a relatively short lifetime because the regolith buildup is happening constantly," co-author Professor Peter Schultz, from Brown University, said in a statement. "So when we see them, there needs to be some explanation for how and why they were exposed in certain locations."
The key to this work is in the difference in temperature between lunar regolith and these rocks. During the lunar night, which lasts 14 days, the exposed rocks stay warmer. Lead author Adomas Valantinas spotted their heat signature using the NASA's Lunar Reconnaissance Orbiter. Valantinas found more than 500 patches of exposed bedrock.
A crucial find in this study is that the newly observed ridges match extremely well with a network of ancient cracks in the lunar crust detected in 2014 by NASA’s GRAIL mission. This suggests, according to the scientists, that these ancient magma intrusions pushed upwards, exposing the rocks. A movement that might be still going on today.
"It's almost a one-to-one correlation," Schultz added. "That makes us think that what we're seeing is an ongoing process driven by things happening in the Moon's interior."
The Moon has its own quakes but it hasn’t got the complex flurry of activity that goes on under our feet. So where do these ridges come from? Valantinas and Schultz point the finger at the catastrophic impact that created the South Pole–Aitken basin. About 4.3 billion years ago, an object about 200 kilometers across hit the Moon at a shallow angle, creating the largest known crater in the Solar System. It appears the ancient impact still has an effect on the Moon, with the surface still adjusting to the event.