Last week, I told you all about InSight detecting its first likely Marsquake. In the article, I mentioned how scientists have been studying quakes on the moon since the Apollo missions.
Recently, Nature Geoscience published a new paper where they took another look at these shallow moonquakes to establish possible connections to some very young surface features, known as lobate thrust fault scarps.
Our moon has these basins called “mare” where it is thought that the last geologic activity occurred long before the dinosaurs roamed Earth. These mare, thought to be tectonically dead, were surveyed using over 12,000 images taken by the Luna Reconnaissance Orbiter Camera (LROC).
It was revealed that at least one of the lunar mare has been cracking and shifting as much as other parts of the Moon. In fact, it’s possible that this is still happening.
“Wrinkle ridges” are curved hills and shallow trenches that are thought to be created by a lunar surface that is contracting as the Moon loses heat and shrinks. These features were revealed in the images taken by LROC and the findings were published in Icarus on March 7, 2019.
While previous research had found similar features in the Moon’s highlands, these wrinkle ridges have never been seen in the basins, until now.
Nathan Williams, a post-doctoral researcher at JPL, led the study that was published in Icarus. He and his co-authors focused on a region known as Mare Frigoris (Cold Sea) that is near the Moon’s north pole.
In this study, they estimated that while some of the ridges may have emerged in the last billion years, while others might be no older than 40 million years. In geologic terms, that’s pretty young, especially given that these basins were thought to have been dead for the last 1.2 billion years.
Because there is no liquid core, or molten movement under the surface of the Moon, there are no tectonic plates. Instead, the tectonic activity happens as the Moon slowly loses heat from when it was formed billions of years ago. And this heat loss is causing the interior to shrink, thus crinkling the surface which creates these distinctive features.
“The Moon is still quaking and shaking from its own internal processes,” Williams said. “It’s been losing heat over billions of years, shrinking and becoming denser.”
So how are scientists able to determine how old these wrinkled ridges are?
Easy – by studying impact craters.
As meteor impacts happen, the surface material is flung up, covering nearby terrain. More impacts mean more debris. This process, known as impact gardening, alters the landscape. Because smaller craters (about the size of a football field) can typically fill to the brim with this type of debris in under a billion years, this gives scientists a basis for time measurement.
Since the images captured by LROC revealed crisp tectonic features, like the wrinkle ridges that cut through the debris, this allowed Williams and his team to deduce that the ridges emerged within the past billion years or so. And these wrinkle ridges are slowly giving the Moon a raisin-like appearance.
Not to worry, though. The lunar shrinkage is indictable to the naked eye. It will still be eons before life on our planet notices measurable changes to the Moon when it’s full. Until then, take yourself outside and look up! The Moon still shines in all her lunar glory, and Jupiter has become visible in the night sky, once again. And you never know what else you’ll see, if you just keep your eyes to the skies!
And if you have a question about the universe, send it to firstname.lastname@example.org and I’ll feature it in an upcoming article!