New MIT research focusing on the gravitational signature of craters on the far side of the Moon is shedding light on the nature and origin of the Late Heavy Bombardment (LHB), as well as the earliest life-supporting processes that took place in our solar system.
The research drew on data from NASA's twin Gravity Recovery and Interior Laboratory (GRAIL) spacecraft. The GRAIL mission mapped the gravitational profile of around 1,200 craters on the Moon's far side by observing the push and pull between the spacecraft as they passed over the lunar surface.
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The team from MIT then subjected the data to Bouger correction, a process that removed the gravity readings created by mountains, valleys and other surface features. This left only gravitational readings taken from within the Moon's crust, allowing the researchers to determine whether impacts during the LHB and after had the effect of increasing or decreasing porosity.
According to the results of the study, the upper crust of the lunar highlands, one of the most ancient areas on the Moon, was completely pulverized during the LHB, an epoch that occurred roughly 3.9 billion years ago and lasted between 20 to 200 million years, and which saw the solar system subjected to an intense barrage of asteroid impacts.
This period of bombardment opened up great fractures in the Moon's surface and made the crust extremely porous. Surprisingly, the data also appears to show subsequent impacts having the reverse effect of reducing the porosity of Earth's closest companion.
The researchers determined that asteroids around 30 m (100 ft) in size had pummeled the upper layer of the Moon's crust, known as the megaregolith, punishing it to the extent that while further impacts may have slightly increased or decreased porosity, the average consistency of the layer could not be greatly altered. In contrast deeper layers of the crust were not so badly damaged, meaning that their porosity could still be altered by larger impacts.
By observing such structural characteristics on the Moon that stem from the LHB, researchers could potentially gain insights into the processes surrounding the creation of early life in our solar system.
"The whole process of generating pore space within planetary crusts is critically important in understanding how water gets into the subsurface," states research scientist Jason Soderblom, of MIT’s Department of Earth, Atmospheric and Planetary Sciences. "On Earth, we believe that life may have evolved somewhat in the subsurface, and this is a primary mechanism to create subsurface pockets and void spaces, and really drives a lot of the rates at which these processes happen. The Moon is a really ideal place to study this."
Furthermore, by studying the gravity signatures of larger subsurface craters, the researchers believe that they may in the future be able to ascertain the origin of the LHB, settling the argument as to whether the impactors came from the colossal asteroid belt surrounding our solar system, or if they invaded from even farther away.
A paper on the findings has been published in the online journal Geophysical Research Letters.