In addition to being one of the major plot points of my favorite video game, Portal 2, the Moon has been a source of scientific research for centuries. New research in the journal Nature Geoscience shows just how porous the Moon’s crust is. Porosity is a measure of the amount of empty space between rock particles.

In a period between 4.4 and 3.8 billion years ago, the Moon was hit by a significant number of space rocks during a time called the Heavy Bombardment. Previous assumptions thought that the Moon’s porosity happened evenly during the Bombardment. The new study from MIT found that the majority of the Moon’s crust was altered in a series of massive impacts early on, not spread out. The later craters actually compressed the surface. Also, the Moon may have only been hit by two times the impacts on its surface, not more as previously thought. According to study co-author Jason Soderblom: We know the moon was so bombarded that what we see on the surface is no longer a record of every impact the moon has ever had because, at some point, impacts were erasing previous impacts.

To determine these two things the team used data on 77 moon craters from NASA’s Gravity Recovery and Interior Laboratory, GRAIL, spacecraft. The 77 craters spanned the oldest through the newest parts of the Moon. The researchers analyzed the craters by age, size, and location. Using the youngest craters as a start, they computed how many impacts were needed to match the observed porosity of the oldest craters. The older craters were twice as porous as the younger craters.

The previously mentioned lower rate in the later period sets a bound on the asteroid impacts across the rest of the solar system and how cratering affects rocky bodies.

More Information

MIT press release

“Bombardment history of the Moon constrained by crustal porosity,” Ya Huei Huang et al., 2022 July 7, Nature Geoscience