The Moon is rusting - thanks to 'wind' blown all the way from Earth

"Scientists have found that oxygen particles blown from Earth to the Moon can turn lunar minerals into hematite, also known as rust. The discovery adds to researchers' growing understanding of the deep interconnection between Earth and the Moon - and shows how the Moon keeps a geological record of those interactions, says Ziliang Jin, a planetary scientist at Macau University of Science and Technology in China. He and his colleagues reported their findings earlier this month in Geophysical Research Letters."

"Most of the time, both Earth and the Moon are bathed in a stream of charged particles emanating from the Sun. But for around five days each month, Earth passes between the Sun and the Moon, blocking most of the flood of solar particles. During that time, the Moon is exposed mainly to particles that had been part of Earth's atmosphere before blowing into space - a phenomenon known as Earth wind."

"In 2020, scientists reported that India's Chandrayaan-1 mission had spotted hematite near the Moon's poles. Hematite is an iron-rich mineral that can form when rocks react with water and oxygen. But the Moon's chemical environment isn't conducive to the presence of oxygen, meaning that the oxygen for the hematite might have arrived from somewhere else. The 2020 paper's authors proposed that it might have arrived in the Earth wind."

Earth periodically shields the Moon from solar wind for about five days each month, exposing the lunar surface mainly to ions from Earth's upper atmosphere known as Earth wind. Earth wind carries hydrogen, oxygen, and nitrogen ions that can implant into the upper layers of lunar soil and drive chemical reactions. Hematite, an iron-rich mineral formed by reaction with oxygen and water, was detected near the lunar poles. Laboratory simulations accelerating hydrogen and oxygen ions into iron-rich lunar mineral crystals produced oxidation consistent with hematite formation, indicating that oxygen from Earth's atmosphere can create rust on the Moon.

Read at Nature