The Moon is rusting – and Earth is to blame

The Moon has long been viewed as dry and nearly devoid of atmosphere. But recent research reveals something unexpected: rust is forming on its surface. The surprising cause isn’t water but oxygen escaping from Earth’s atmosphere. This oxygen reaches the Moon through the so-called Earth Wind – a stream of particles released from the planet’s upper atmosphere when Earth lies between the Sun and the Moon. These particles then settle on the lunar surface.

In 2020, India’s lunar mission Chandrayaan-1 detected the iron-rich mineral hematite near the Moon’s poles. Hematite is a reddish, crystalline form of iron oxide (Fe₂O₃), commonly linked to rust on Earth. Since it typically forms in the presence of water and oxygen, its discovery on the dry, nearly atmosphere-free Moon was initially a mystery. But a study published on September 2, 2025, in Geophysical Research Letters now provides experimental evidence of its origin – the rust appears to come from Earth.

For about five days each month, when Earth moves between the Sun and the Moon, it blocks the solar wind. During this time, ions of oxygen, hydrogen and nitrogen can escape from Earth’s upper atmosphere and reach the Moon. These particles settle into the lunar surface layer and trigger chemical reactions. Laboratory experiments led by Ziliang Jin at the Macau University of Science and Technology showed that oxygen ions promote the formation of hematite, while hydrogen can partially reverse the process.

The findings highlight that Earth and the Moon are more geochemically connected than previously believed. The Moon preserves evidence of its long-term interactions with Earth, effectively serving as a geological archive. Upcoming missions to retrieve lunar samples containing hematite are expected to confirm whether the oxygen truly originates from Earth. If so, this could significantly reshape our understanding of the Earth–Moon relationship.