Scientists believe that about 4 billion years ago, during a period called the Late Heavy Bombardment, the moon took a severe beating, as an army of asteroids pelted its surface, carving out craters and opening deep fissures in its crust. Such sustained impacts increased the moon’s porosity, opening up a network of large seams beneath the lunar surface.
Now scientists at MIT and elsewhere have identified regions on the far side of the moon, called the lunar highlands, that may have been so heavily bombarded — particularly by small asteroids — that the impacts completely shattered the upper crust, leaving these regions essentially as fractured and porous as they could be. The scientists found that further impacts to these highly porous regions may have then had the opposite effect, sealing up cracks and decreasing porosity.
Scientists believe that about 4 billion years ago, during a period called the Late Heavy Bombardment, the moon took a severe beating, as an army of asteroids pelted its surface, carving out craters and opening deep fissures in its crust. Such sustained impacts increased the moon’s porosity, opening up a network of large seams beneath the lunar surface.
Now scientists at MIT and elsewhere have identified regions on the far side of the moon, called the lunar highlands, that may have been so heavily bombarded — particularly by small asteroids — that the impacts completely shattered the upper crust, leaving these regions essentially as fractured and porous as they could be. The scientists found that further impacts to these highly porous regions may have then had the opposite effect, sealing up cracks and decreasing porosity.
The researchers observed this effect in the upper layer of the crust — a layer that scientists refer to as the megaregolith. This layer is dominated by relatively small craters, measuring 30 kilometers or less in diameter. In contrast, it appears that deeper layers of crust, that are affected by larger craters, are not quite as battered, and are less fractured and porous.
Jason Soderblom, a research scientist in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says the evolution of the moon’s porosity can give scientists clues to some of the earliest life-supporting processes taking place in the solar system.
“The whole process of generating pore space within planetary crusts is critically important in understanding how water gets into the subsurface,” Soderblom says. “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.”
Soderblom and his colleagues, including Maria Zuber, the E.A. Griswold Professor of Geophysics and MIT’s vice president for research, have published their findings in the journal Geophysical Research Letters.
Researchers analyzed the gravity signatures of more than 1,200 craters (in yellow) on the far side of the moon. Credit MIT researchers.
Read more at MIT.
