Impact History of Earth-Moon System

The Moon’s surface contains a complete record of the impact history of the inner solar system that stretches back to the formation of the Earth-Moon system, unlike the Earth, where rocks are recycled through plate tectonics or weathered away by fluvial and aeolian processes. Understanding the Moon’s impact history can therefore help us better understand the impact history of the Earth-Moon system and how these impacts affected our own planet.

The brightly illuminated Earth in nearly full view over the dimly lit lunar surface in the foreground. The Earth is seen in the center but is partly cut off on the bottom by the Moon’s surface. There is a flurry of white clouds in the southern hemisphere past the tip of Africa. The African continent peaks through Earth’s busy atmosphere and the sapphire blue ocean shines brilliantly around it.

The Lunar Reconnaissance Orbiter (LRO) captured this breathtaking image of Earth as it was orbiting the Moon. This is a composite image from a series of pictures taken October 12, 2015, when the spacecraft was approximately 134 km above the lunar crater, Compton. The image was created by using the high-resolution black-and-white Narrow Angle Camera (NAC) and lower-resolution color imaging Wide Angle Camera (WAC). These two cameras used together allowed scientists to put a clear and colorful image together of the Earthrise on the Moon.

Returning samples from the giant South Pole-Aitken (SPA) Basin on the far side of the Moon will enable us to determine the age of the basin and anchor the early Earth-Moon impact-flux curve. Returned samples and studies of crater statistics indicate that the lunar impactor flux was relatively constant over the last 3 billion years but was much higher before this time period. Some models of planet formation suggest there was a “late heavy bombardment” period around 3.9 billion years (just about the time life on Earth was emerging), when the impact flux in the inner solar system was incredibly high. Dating SPA will help us better determine whether there was a spike in impacts during this time interval, and if so, how that may have affected life on Earth.