While most scientists believe that the moon was severely pummeled by an array of asteroids roughly four billion years ago, a new study from research scientists at MIT and elsewhere has found that this event may have had a greater-than-expected impact on the lunar surface.
Known as the Late Heavy Bombardment, the sustained asteroid impacts were so heavy in some regions of the dark side of the moon that they completely shattered the upper crust. These areas, known as the lunar highlands, were left as fractured and porous as they could be – until additional impacts sealed back up the previously created cracks.
Jason Soderblom of the MIT Department of Earth, Atmospheric, and Planetary Sciences and his fellow investigators explained in a statement that they observed this effect in the upper layer of the lunar crust (also known as the megaregolith). Small craters no more than 30 km in diameter dominate this layer, while deeper layers have larger craters and less porous terrain.
The authors, who published their findings in the journal Geophysical Research Letters, used data from the NASA Gravity Recovery and Interior Laboratory (GRAIL) satellites to map the gravity field in and around more than 1,200 craters in the lunar highlands, then used that information in a series of calculations to determine if an impact increased or decreased porosity.
For craters smaller than 30 km in diameter, Soderblom’s team found impacts that both increased and decreased porosity in the upper layer of the moon’s crust. Larger craters, on the other hand, were found much deeper in the moon’s crust and only increased in porosity further down, which indicates that the deeper layers are less fractured than the megaregolith.
Research could provide insight on origins of life, Late Heavy Bombardment
The evolution of the moon’s porosity could give scientists new insight into some of the earliest life-supporting processes occurring in the solar system, as the interaction of water and rock can provide a significant source of energy and may have played a key role in the evolution of life on Earth, Soderblom explained to redOrbit via email.
“A rocky layer that is porous and fractured has an increased surface area, which increases the rates at which water-rock reactions occur. Understanding how porosity formed and evolved in Earth’s crust, therefore provides insight into these reaction rates,” Soderblom said. “The moon has undergone little modification over the lifespan of the solar system, and so it provides us a great way to look back in time at what the Earth, and the other terrestrial planets, might have looked like in the early solar system.”
In addition, he and his co-author hope to discover where these different types of impactors came from, and as a result, to understand more about the origins of the Late Heavy Bombardment. As Soderblom explained, the total number of craters that formed on the moon (its cumulative record of craters) is one of “the great outstanding questions in the history of the solar system.”
However, the far side of the moon simply has too many craters to retrieve this information, he said. Thus, he and his colleagues hope to use the structure of the subsurface to retrieve this data. To this end, they are developing a model that will simulate the evolution of impact-generated porosity in the lunar subsurface.
“Knowing this will allow us to understand the magnitude of the Late Heavy Bombardment – and, in fact, test whether it occurred at all – and to investigate the significance of this event for other planetary bodies throughout the Solar System,” he concluded.
—–
Feature Image: MIT
Comments