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Unlike Earth, the Moon has preserved radioactive debris from supernovae dating back 80–100 million years. The surface of our planet’s natural satellite conceals radioactive remnants of ancient stellar explosions, resembling glitter mixed with cosmic dust.
An innovative computer model has allowed experts to distinguish microscopic dust from supernova explosions from ordinary lunar soil. This transforms the moon’s surface into a veritable time capsule, preserving comprehensive data on ancient cosmic catastrophes that occurred near the Solar System as it traveled through its orbit around the Galaxy.
The death of massive stars is accompanied by powerful explosions that scatter enormous amounts of matter into the surrounding space, including high-speed radioactive isotopes. Some particles of this stellar debris enter our system and settle on the surfaces of its planets and moons. Analysis of radioactive elements in deep-sea sediments on Earth, along with studies of samples of lunar regolith brought back by the Apollo mission crews, points to the existence of two relative surges in supernova activity that occurred approximately 2.3 and 7.3 million years ago.
According to planetary scientist Emily Costello of the University of Hawaii at Manoa, the ability to use the remnants of extinct stars to reconstruct the grand history of our cosmic neighborhood is fascinating, provided we have a clear understanding of the methodology for interpreting this stardust.
At the same time, most geological evidence of such a legacy on Earth has been irretrievably lost due to the constant effects of wind and water erosion, as well as processes of tectonic shift and plate subduction. As a result, reliable terrestrial records cover a period of only up to 10 million years. Unlike our planet, the Moon presents entirely different conditions: the absence of an atmosphere precludes weathering or rain erosion, and plate tectonics are completely absent there. Consequently, the lunar surface is capable of preserving a record of supernova explosions dating back 80–100 million years or even much further.
Despite the absence of the destructive factors common on Earth, the Moon is subject to another phenomenon that experts call “impact gardening.” The fall of celestial bodies – from microscopic micrometeorites to massive asteroids – constantly churns and mixes the upper layers of regolith, blending even the radioactive debris from supernovae into a single mass.
To make sense of this chaos and determine the specific depths to which various radioisotopes have sunk, a team led by Costello developed a mathematical algorithm capable of deciphering the treasures hidden in the lunar soil.
Costello explained that creating a detailed model of impact gardening required balancing an entire system of physical processes. These included impact compaction, rock removal, radioactive decay, and space weathering, all of which occur simultaneously within a single, continuous physical system. The proposed mathematical approach treats soil mixing as a constant tug-of-war between the processes of burying material and its subsequent excavation due to new impacts, while simultaneously accounting for the natural decay of radioactivity and recording the exact times and locations of new stardust influxes from individual explosions.
The researchers confirmed the validity of the model by comparing the calculated values of radioisotope concentration and depth of occurrence with real data obtained from the analysis of Earth’s ocean sediments and samples from the Apollo program.
Costello noted that when she first presented the results of her calculations to her colleagues, they were impressed by the high degree of agreement between the theoretical model and the actual measurements. This level of agreement between empirical data and physical calculations is extremely encouraging and significant.
The developed system accurately predicted the depth distribution of iron-60 in Apollo regolith samples, as well as other heavy elements, including plutonium-244, iodine-129, hafnium-182, and curium-247, which have been trapped beneath the surface for extended periods.
However, a full-fledged scientific breakthrough is expected once participants in future Artemis expeditions bring back to Earth new samples of lunar soil extracted from greater depths.
Costello emphasized that new samples from the Moon’s depths, combined with the developed mixing model, will help shed light on previously unknown chapters in the history of stellar explosions. Understanding the physics of regolith mixing will enable scientists to properly interpret the mixed layers once astronauts retrieve deeper cores, allowing for a complete reconstruction of the Solar System’s path through the Galaxy.
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