Earth’s atmosphere may have been leaking onto the Moon for billions of years.
Light volatile elements found in the lunar regolith, such as nitrogen and noble gases, appear to come from a mix of solar wind and ions escaping from Earth’s atmosphere. New computer simulations, reported December 11 in Communications Earth & Environment, show that this transfer happens efficiently only when the Moon orbits through Earth’s magnetotail, a region extending from the planet’s nightside where the magnetic field stretches out like a windsock.
The findings suggest that the non-solar parts of these elements in lunar soil were implanted mostly during Earth’s long history with an active magnetic field, rather than any short period without one in the distant past.
“The non-solar contribution to the lunar soil is best explained by implantation during the long history of the geodynamo under present-day solar wind conditions, rather than by any brief, putatively unmagnetized epoch of the early Archean Earth,” the researchers write.
The Moon lacks a thick atmosphere or strong magnetic field, making its surface directly exposed to incoming particles. Solar wind, a stream of charged particles from the Sun, implants ions into the lunar soil. But elements like nitrogen show abundances and isotopic ratios that do not match solar wind alone, pointing to another source.
In the study, the team used three-dimensional magnetohydrodynamic simulations to model how solar wind interacts with Earth’s atmosphere under different conditions: one with Earth’s current magnetic field, generated by its dynamo in the core, and another without it, representing a possible early phase of Earth around 4 billion years ago. They tracked how atmospheric ions escape and mix with solar wind, eventually reaching the Moon.
The simulations reveal that Earth’s magnetic field shapes the escape of atmospheric ions. In the magnetized case, the field creates a protective bubble but also extends the atmosphere outward, allowing ions to be picked up by solar wind in the magnetotail. Without a magnetic field, the transfer is less efficient overall, and the stronger ancient solar wind would have dominated, leaving less room for Earth’s contribution.
The models match data from Apollo samples, which show isotopic mixtures of elements like nitrogen, hydrogen, helium, neon, and argon. These mixtures fit curves corresponding to an escape boundary in Earth’s atmosphere no lower than about 190 kilometers, where ions are freed to flow outward.
“Our results indicate that the elemental abundances of Apollo samples are highly sensitive to Earth’s hydrodynamic escape boundary, which, at the time of ion implantation, was never smaller than 190 km,” the researchers note.
This implantation focuses on the Moon’s nearside, facing Earth, because the magnetotail directs the flow there. The farside likely receives more pure solar wind. Buried layers of lunar soil, undisturbed by recent impacts, could preserve a record of how Earth’s atmosphere evolved over time, including changes in composition that might relate to the rise of life.
“This further suggests the history of the terrestrial atmosphere, spanning billions of years, could be preserved in buried lunar soils,” the team concludes.
Citations
S. Paramanick et al. Terrestrial atmospheric ion implantation occurred in the nearside lunar regolith during the history of Earth’s dynamo. Communications Earth & Environment. Published online December 11, 2025. DOI: 10.1038/s43247-025-02960-4
