Lunar soil reads as a cosmic time capsule for exploding stars

When a star enters the final stages of its life, it explodes in a bright, powerful supernova, scattering material throughout the universe. A recent study led by a researcher at the University of Hawai'i at Mānoa has found that the lunar soil can serve as a cosmic time capsule for supernovas. The research, published in the journal Physical Review Letters, was conducted by Emily Costello and her team, who created a mathematical model to decode the history stored in the lunar surface.

Unlike deep-sea deposits on Earth, which only preserve interstellar debris for about 10 million years, the lunar regolith provides a long-term cosmic archive that can preserve history spanning 80–100 million years or more. This is because the regolith undergoes continuous mixing through a process called impact gardening, which occurs when meteorites collide with the moon's surface, flipping, mixing, and redistributing the soil over time.

The researchers developed a unified stochastic model that accounts for the various physical mechanisms involved in impact gardening, such as compaction, excavation, radioactive decay, and space weathering. By balancing these forces, the model can accurately separate the broader interstellar signal from local variability. The team validated their model using data from deep-sea sediments on Earth and lunar soil samples collected during the Apollo missions.

By comparing their model to the actual depth-concentration profiles of certain radioisotopes found in Apollo core samples, the researchers were able to demonstrate that their model accurately reproduced these profiles. They then used this validated model to predict how other heavy elements, such as plutonium-244, iodine-129, hafnium-182, and curium-247, would be buried over time in the lunar regolith.

The study's findings have important implications for future lunar exploration. When NASA's Artemis program returns humans to the moon and collects new samples of lunar regolith, researchers can use the gardening model to interpret these samples and gain new insights into the history of supernovas in our solar system. By understanding how stardust is preserved in the lunar soil, scientists can better trace the journey of our solar system through the galaxy.