The Moon was routinely pummelled by massive asteroids and comets during the creation of the solar system around 4.4 billion years ago and it still get hits by celestial objects today, albeit less frequently.
This period of intense bombardment ended around 3.8 billion years ago, leaving behind a heavily cratered face and a cracked and porous crust.
The team has shown through simulations that, early on in the bombardment period, the Moon was highly porous - almost one-third as porous as pumice. This high porosity was likely a result of early, massive impacts that shattered much of the crust.
Scientists have assumed that a continuous onslaught of impacts would slowly build up porosity. The team found that nearly all the Moon’s porosity formed rapidly with these massive impacts and that the continued onslaught by smaller impactors actually compacted its surface. These later, smaller impacts acted instead to squeeze and compact some of the Moon’s existing...