Get the key facts about this story in our quick 1-minute read
- Unexpected discovery: Despite lacking air and water, scientists detected hematite – a form of rust – on the Moon in 2020 via data from India’s Chandrayaan-1 mission
- Rust needs iron, oxygen, and water: While Moon rocks are rich in iron, the necessary oxygen and water shouldn’t be available, making this discovery puzzling
- Earth’s magnetic tail: Earth’s magnetic field stretches into space and forms a ‘tail’ that the Moon passes through for about six days each lunar cycle, near full Moon
- Borrowed oxygen: During those periods, Earth’s oxygen may hitch a ride along the magnetotail to the Moon, supplying the oxygen required for rust formation
- Solar wind protection: Earth’s magnetotail also blocks most of the solar wind’s hydrogen (a reducer that prevents rust) during full Moon, creating a rare window for oxidation
- Moon’s water: Though there’s no liquid water, water molecules and hydroxyl detected on the lunar surface (especially at the poles) could offer the moisture needed for rust to form
- Dust plays a role: Micrometeorite impacts may release or bring water molecules into contact with iron, helping trigger the rusting reaction when conditions align
- Mystery remains: This model explains why rust appears mainly on the near side facing Earth, but minor rust on the far side remains unexplained, and needs more data