The Moon is renowned for its many craters, which still bear the signs of atmospheric turbulence. However, evidence of a series of lava flows that detail a different form of upheaval in the Moon’s past may be found just beneath the fractured lunar surface.
The Planetary Science Institute in Arizona astrophysicist Jianqing Feng, together with colleagues from China and the UK, intended to build on earlier studies of the lunar subsurface that, well, kind of fell flat.
Feng and his coworkers examined information from the Chang’e-4 rover, which touched down on the far side of the Moon in 2019. They also examined data from those earlier investigations. However, this time scientists were able to look deeper into the lunar surface using ground-penetrating radar at lower frequencies because they had access to considerably more data beyond Chang’e-4’s first few lunar days.
On Chang’e-4, there is a lunar penetrating radar. As the rover plods ahead, it sends pulsed signals into the lunar subsurface. These radar signals are bounced back up to the surface, where the receiver is waiting, if they clearly contrast two subsurface materials with distinct characteristics.
The top 40 meters (131 feet) of the Moon included only an old crater that was obscured by soil and debris from surrounding impacts.
Things started to get a little more interesting below 90 meters (295 feet).
Feng and colleagues wrote in their research, “Through our investigation, we have uncovered numerous strata in the upper 300 meters, which presumably reflect a sequence of basalt eruptions that occurred billions of years ago.
Recent debates have focused on lunar volcanism. On the opposite side of our satellite, researchers discovered an unusual hotspot last month that might be a hidden mass of hardened magma created by a previously unidentified sort of volcanism.
A billion years longer than previously believed, lava flowed from volcanoes on the Moon, as shown by the first lunar rocks to be collected in more than four decades.
Another trace of that lengthy history can be seen in the layers of lava that Feng and his team discovered. Deeper layers were discovered to be thicker, but they were thinner as they got closer to the surface, indicating a “gradual depletion of internal thermal energy that drove [lunar] volcanism” and “a decrease in eruption scale over time.”
The lava flows narrowed to around 5 meters wide at shallower depths close to the landing site, where the thickest layers were about 70 meters (or 230 feet) broad.
A thin layer of lunar dirt is sandwiched between the hardened rock in what Feng and colleagues believe to be at least three or four significant lava flow events, some of which appear to be relatively close together.
Researchers claim these layers are typical of underlying structures around the Von Kármán crater, where Chang’e 4 has been roving, after comparing their findings to those from the previous lunar module, Chang’e 3.
The only thing we can infer about the chronology of lunar volcanic episodes from remote sensing data is that they seem to get smaller with time until the Moon’s thermal energy peaked. Our understanding of the Moon’s most recent volcanic activity surges has some quirks that have recently been worked out by other investigations.
Low-frequency lunar penetrating radar data interpretation is a topic of discussion among space scientists. Some people claim that the subsurface layers discovered in earlier investigations are simply system noise. So anticipate that these fresh results will also be examined.
The study has been published in the Journal of Geophysical Research: Planets.