An article published in the journal “Geophysical Research Letters” describes a research on the implications of multiple asteroid impacts on the Moon some four billion years ago. Using data collected by NASA’s GRAIL (Gravity Recovery and Interior Laboratory) twin space probes, a team of scientists led by MIT (Massachusetts Institute of Technology) discovered a significant porosity in the lunar surface and a network of large seams below it.
The mission of Ebb and Flow, the GRAIL spacecraft, ended in late 2012 with them crashing on the Moon’s surface. This mission was primarily intended to create a gravitational map of the Moon to analyze its characteristics. The two twin probes collected data until almost the last minute so their analysis continued in time and they were used for this research on the Moon’s crust.
In particular, the researchers focused on the effects of the asteroid impacts that occurred about four billion years ago. This is the time when there was the so-called late heavy bombardment. At that time, a huge amount of asteroids hit planets and satellites and the Moon still bears its consequences.
The researchers identified regions on the far side of the Moon called the lunar highlands that may have been bombarded in a way so intense, particularly by small asteroids, that the impacts have completely shattered the upper crust. This left those regions as porous and fractured as possible. Subsequent impacts may have had the opposite effect, sealing the fractures and decreasing porosity.
The effects were observed on the upper layer of the lunar crust, the one scientists call megaregolith. This layer is dominated by relatively small craters, with a diameter of 30 kilometers (less than 19 miles) or less. The lower layers of the crust contain instead larger craters but less fractured and porous.
The data from the GRAIL mission alowed to map the gravitational field in the area of more than 1,200 craters on the far side of the Moon. These lunar highlands represent the area with the greatest amount of craters and they’re also the most ancient. To map the gravity below the surface, in the lunar crust, the researchers subtracted the gravitational effects of mountains, valleys and other topological features from the total gravitational field.
It’s not just a scientific research to better understand what has happened during the late heavy bombardment. MIT researcher Jason Soderblom stated that the process of porosity generation in planetary crusts is critical in understanding how water gets into the subsurface. On Earth, life might have evolved somewhere in the subsurface so it’s important to understand these mechanisms and the Moon, where there have been limited changes to the crust, is the ideal place to study them.
[ad name=”eBayUSUKNASA”]
