ISRO's Chandrayaan 1 Spots Rusting On The Moon

• 05 Sep 2020

• By studying data from the Chandrayaan-1's Moon Mineralogy Mapper instrument (M3) built by the National Aeronautics Space Administration’s (NASA) Jet Propulsion Laboratory (JPL), scientists think that the Moon may be rusting along the poles.

A Riddle

• The occurrence of rust is a riddle because even though the Moon is known to have iron-rich rocks littered across the surface, it’s not known for the presence of water and oxygen — two elements that need to interact with iron to create rust.

Explanation by the Researchers

• Researchers at the National Aeronautics and Space Administration (NASA) believe that this could because Earth’s own atmosphere.

Role of Earth’s Atmosphere

The Puzzle of Oxygen

• The Moon is constantly bombarded by solar particles coming off the Sun. Without an atmosphere to protect itself, the hydrogen should make it difficult for rust to form because Hydrogen is a reducer, it adds electrons to the material it touches. For iron to rust, it needs the opposite — an oxidiser which removes electrons instead.
• Earth’s magnetotail — the part of its magnetic atmosphere that extends away from the Sun — is capable of blocking out 99% of the solar wind aimed at the Moon when it’s in its Full Moon phase.
• That part of the lunar cycle gives iron on the Moon occasional windows of opportunity for rust to form.
• Earth’s magnetotail does more than just provide the Moon with a shield. During that interaction, some of the oxygen from the planet also gets transferred over. This was confirmed by Japan’s Kaguya orbiter in 2007.
• So, even though the Moon isn’t rich in oxygen, it does have access to oxygen during the same window of opportunity when it’s not being bombarded with hydrogen.

The Puzzle of Water

• Even though the rest of the Moon is bone dry, its poles have long been suspected of hosting water. Albeit only in shadowed craters located on the far side of the Moon — far from where the rust has been detected.
• Researchers propose that fast-moving dust particles, which regularly pelt the Moon, could release surface-borne water molecules and mix them with iron in the lunar soil. Compounding the interaction, the resulting heat from these impacts could increase the oxidation rate.
  

So if all three ingredients are in place — a Full Moon phase, water molecules and oxygen travelling from Earth — the perfect storm to create rust can in fact occur.

Questions still left Unanswered

• Exactly how water is interacting with lunar rocks.
• Why rusting is occurring on the far side of the moon, where it’s blocked off from Earth’s oxygen.