The soil covering the moon may contain a remarkable record of ancient stars that exploded millions of years ago.
Scientists have developed a new way to read this scrambled history, potentially turning lunar soil into a cosmic archive of our solar system’s journey through the Milky Way.
The study, led by University of Hawaiʻi at Mānoa researcher Emily Costello, was published in Physical Review Letters.
Massive stars can end their lives in enormous explosions called supernovas. These explosions release material into space, including radioactive forms of elements that can travel hundreds of light-years.
Some of this material eventually reaches Earth and the moon.
Scientists have previously found evidence of ancient supernovas in deep-sea sediments on Earth. However, these deposits generally preserve a record extending only about 10 million years into the past. The moon could provide a much longer history.
According to Costello, lunar soil, known as regolith, may preserve evidence stretching back 80 million to 100 million years or even longer.
Reading that record is difficult because the lunar surface is constantly being disturbed.
Unlike Earth, the moon has no thick atmosphere to protect it from incoming space rocks. Meteorites ranging from tiny particles to large asteroids continually strike its surface. Over millions of years, these impacts dig up, bury and redistribute lunar material in a process called “impact gardening.”
This means that radioactive material deposited by a supernova does not remain neatly arranged in layers. Instead, it gradually becomes mixed throughout the soil.
Costello and her colleagues developed a mathematical model designed to reconstruct this scrambled history. The model considers several processes happening at the same time, including impacts that bury or excavate material, soil compaction, radioactive decay and changes caused by exposure to space.
It also calculates when radioactive material from individual supernova events arrived on the moon and how that material would subsequently move through the lunar soil.
Scientists already have evidence that supernovas occurring hundreds of light-years away sent radioactive material toward our solar system around 2.3 million and 7.3 million years ago.
To test their model, the researchers compared its predictions with measurements from lunar soil cores collected during the Apollo missions. The model successfully reproduced patterns showing how radioactive isotopes were distributed at different depths.
It also accurately predicted the distribution of iron-60, a radioactive isotope associated with supernova explosions, in Apollo lunar samples.
The researchers then used the model to predict how other rare radioactive elements, including plutonium-244, iodine-129, hafnium-182 and curium-247, could become buried and redistributed over millions of years.
The findings could be particularly useful as humans prepare to return to the moon.
NASA’s Artemis program is expected to provide opportunities to collect new lunar samples, including deeper cores that may contain much older material than samples currently available.
By combining these future samples with the new model, scientists may be able to reconstruct supernova activity over tens of millions of years. This could reveal when exploding stars scattered material across our solar system and provide clues about how the sun, Earth and moon have traveled through the galaxy.
In this way, ordinary-looking moon dust could become a time capsule preserving the remains of stars that disappeared millions of years ago.
Source: KSR.
