Late bombardment of the Moon revealed

The moon with clearly visible craters formed by asteroid impacts. NASA/Goddard Space Flight Center Planetologists from Münster investigate origin of heavy bombardment of the Moon 3.9 billion years ago / Publication in "Science Advances" The lunar surface is covered by numerous craters that date back to the impacts of asteroids. Age determinations on lunar rocks formed during these impacts show a surprising clustering at ages of about 3.9 billion years before present, or about 500 million years after the Moon was formed. These observations have led to the theory of a Late Heavy Bombardment of the Moon (or LHB). But what was the origin of this late bombardment and where did the asteroids that hit the Moon come from? Scientists discuss two possibilities. One is that these bodies could represent the leftover material from the main phase of Earth's formation that hit the Moon with continuously decreasing frequency. Another hypothesis is that about 3.9 billion years ago, instabilities in the orbits of the gas giant planets led to a sudden sharp increase in impacts from asteroids and comets from the outer solar system.