The Moon’s surface is covered by impact craters, ranging from microscopic pits to massive basins over 1,000 kilometres across.
These craters formed primarily during the Late Heavy Bombardment period about 4 billion years ago, when the inner Solar System experienced an intense period of asteroid and comet impacts.
Unlike Earth, where weathering, erosion, and tectonic activity continually reshapes the surface, the Moon lacks an atmosphere and significant geological activity, allowing these impact features to remain preserved for billions of years.
This remarkably preserved cratering record serves to capture crucial history of the formation and evolution of our Solar System.
During the formation of craters a significant quantity of the ejected lunar material achieves the Moon’s escape velocity and reaches Earth. Studying these rocks helps us to understand how material moves between the two bodies.
A team of researchers have turned their attention to this study and their paper has recently been published.
The research, led by Jose Daniel Castro-Cisneros utilises better computer models than previous studies to track how Moon debris reaches Earth.
The study uses simulations to examine more starting conditions over longer time periods to better estimate how much lunar material reaches Earth and whether it contributes to near Earth objects.
The team also hoped that by studying Moon debris trajectories, they would be able to piece together Earth’s impact timeline and how it affected life and geology. They are also especially interested in objects like Kamo’oalewa, believed to be between 36-100 metres in diameter orbiting near Earth that might actually be a piece of the Moon.
Previous studies of lunar ejecta were improved upon by using the REBOUND simulation package to track particles from the Moon for 100,000 years. Unlike earlier work that used separate phases, the team simultaneously model Earth and the Moon using a more realistic ejection velocity distribution.
They recorded data every five years and collision events defined as ejecta reaching 100 km above Earth’s surface, providing a more comprehensive picture of how material transfers from the Moon to Earth.
The model employed, used simplified vertical impacts, though natural oblique impacts would direct more material toward Earth at lower angles, the approach simplified the process.
Current environmental conditions were assumed but historically, when the Moon was closer and experiencing heavier bombardment (over 1.1 billion years ago), even more lunar material would have reached Earth. Future research should incorporate oblique impact models and ancient orbital configurations to better understand early Earth-Moon material exchange.
The team were able to conclude that, following lunar impacts, Earth collects about 22.6% of the ejected material over 100,000 years, with half of these collisions occurring within the first 10,000 years.
The collision rate follows a power-law distribution over time (a relationship where a change in one quantity results in a proportional relative change in another) independent of the initial size of those quantities.
Material launched from the Moon’s trailing side has the highest Earth collision probability, while the leading side produces the lowest.
When hitting Earth, lunar ejecta travel at 11.0-13.1 km/s and predominantly strike near the equator (with 24% fewer impacts at the poles). These impacts are nearly symmetrically distributed between morning and evening hours, peaking around 6 AM/PM.
This research significantly advances our understanding of lunar-Earth material exchange, showing that nearly a quarter of lunar impact ejecta reaches Earth—half within just 10,000 years.
The findings about equatorial impact concentration and the importance of lunar launch location reveal previously unknown patterns in this process.
These results enhance our understanding of the Earth-Moon system’s shared impact history while supporting the lunar origin hypothesis for objects like Kamo’oalewa.
Written by Mark Thompson/Universe Today.
