Secrets of the Lunar Garden: How Meteorites Mix Cosmic Dust express
Lunar soil is a garden that meteorite impacts constantly dig over. Instead of a shovel, asteroids shake up the surface, scattering cosmic dust and bringing deep layers to the top. This cosmic “tending of the bed” goes on for millions of years, creating a uniform layer.
A new computer model has, for the first time, combined two effects of impacts: the transport and mixing of particles. Testing it with data from the Apollo missions, researchers saw how the content of iron-60—alien atoms that came from supernova explosions (studied by Zwicky)—changes with depth. It turned out that stardust is distributed evenly, without mixing with local iron. The lunar garden works so thoroughly that the soil in different spots on the planet is identical, as if it’s constantly sifted through a giant sieve. Now the model predicts where to look for traces of even rarer events — for example, plutonium-244, born in the merger of neutron stars.
Original abstract
as written by the authors arXiv:2604.09524
The vertical redistribution of materials in the lunar regolith - ranging from continuously produced space-weathering products to sporadic pulses of supernova- or kilonova-derived isotopes - remains a fundamental problem in planetary science. We present a unified stochastic model of regolith gardening induced by the impact flux. Treating gardening as a competition between impact-driven advection and diffusion predicts the maturity profiles of Apollo cores over more than two orders of magnitude in time ($$1.4 \times 10^7$$ to $$4.5 \times 10^8$$ years). This model describes well the depth profiles of live Fe60 in Apollo regolith samples, suggesting that supernova dust capture is independent of native iron abundance, and is consistent with a uniform influx at the latitudes of the Apollo landing sites. We extend our model to predict lunar signals for live r-process species that might originate from supernovae or kilonovae: Pu244 tied to terrestrial detections, and I129, Hf182, and Cm247 based on r-process calculations. The Pu244/Fe60 depth profile can probe the origin of Pu244, motivating searches in Artemis regolith samples down to depths O(100) cm.
The mixed layer reaches several meters, as if a gardener dug a bed to the depth of a three-story building.
Arthur C. Clarke, in *A Fall of Moondust*, described mining rare resources on the Moon. Perhaps in the future, we’ll go there for traces of supernovae and other cosmic catastrophes.