Earth's magnetic field may move tiny air particles to the Moon ^{CEFR B2}

New simulations from a team at the University of Rochester, published in Nature Communications Earth and Environment, indicate that Earth's magnetic field could have funnelled tiny amounts of the upper atmosphere onto the lunar surface over billions of years. Samples returned by the Apollo missions show the lunar regolith contains volatiles — including water, carbon dioxide, helium, argon and notably nitrogen — amounts that the solar wind alone cannot fully explain. A 2005 proposal suggested terrestrial atmosphere reached the moon only before Earth developed a magnetic field, but the new models reach a different conclusion.

The researchers tested two scenarios with advanced computer modelling: an early Earth with no magnetic field and a stronger solar wind, and a modern Earth with a strong magnetic field and a weaker solar wind. The simulations indicate particle transfer is more efficient in the modern scenario. In that case, charged particles in the upper atmosphere are knocked loose by the solar wind and then guided along Earth's magnetic field lines; some of those lines extend far enough into space to intersect the moon, producing a slow but persistent funneling effect.

The findings imply the moon may hold a long-term chemical record of Earth's atmosphere, climate, oceans and even life, and that greater volatile abundance could ease logistics for a sustained human presence by reducing how much must be shipped from Earth. The study also has broader implications for understanding atmospheric escape on planets such as Mars. The work received funding from NASA and the National Science Foundation.