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Scientists puzzled at discovery of rust on the Moon

Published Sep 4th, 2020 4:26PM EDT
moon rust
Image: NASA

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  • Scientists have discovered traces of rust minerals on the Moon’s surface.
  • The Moon has iron, but no liquid water or oxygen, so rust shouldn’t be possible.
  • A new theory suggests that the Moon gets oxygen particles from Earth’s atmosphere, and tiny bits of water on its surface could trigger the formation of rust.

When you gaze up at the Moon on a clear night you’ll see a big, pale, dusty white orb. Our planet’s friendly little neighbor has always shined a bright white in the night sky — unless you’re seeing it at an extreme angle, in which case it might be slightly off-white — but according to NASA, that’s slowly changing.

The Moon is rusting. Yes, rusting. The Moon’s surface has a lot of iron, but no atmosphere. Mars, the iconic Red Planet, is orange for the same reason, but it’s had a long history and, at one point, a much more robust atmosphere that combined oxygen and water to turn the planet’s surface orange. The Moon doesn’t have that kind of history, but it’s beginning to rust nonetheless.

The discovery, which is the subject of a new paper published in Science Advances, was made using data from the Chandrayaan-1 orbiter. The spacecraft, which was launched by the Indian Space Research Organization (ISRO), studied the makeup of the Moon’s surface from a distance. It found that areas of the Moon appeared to have a mineral called hematite, a form of rust.

With no oxygen or liquid water on its surface, the Moon’s iron shouldn’t have a chance to rust, but it appears to be doing so anyway. The researchers considered many possibilities for why this could be the case and came up with one that seems quite plausible: the Moon’s rusting is Earth’s fault.

“At first, I totally didn’t believe it. It shouldn’t exist based on the conditions present on the Moon,” Abigail Fraeman of NASA’s Jet Propulsion Laboratory said in a statement. “But since we discovered water on the Moon, people have been speculating that there could be a greater variety of minerals than we realize if that water had reacted with rocks.”

So where is the oxygen coming from? As it turns out, despite a lack of atmosphere, the Moon does have a tiny bit of oxygen floating around, courtesy of its host planet, Earth. “Earth’s magnetic field trails behind the planet like a windsock,” JPL explains. “In 2007, Japan’s Kaguya orbiter discovered that oxygen from Earth’s upper atmosphere can hitch a ride on this trailing magnetotail, as it’s officially known, traveling the 239,000 miles (385,00 kilometers) to the Moon.”

The Moon and the Earth aren’t exactly snuggled up next to each other, but they’re close enough that when the Moon is in the right spot, it can take on oxygen from Earth. But this is just one half of the puzzle, and the other big ingredient to be accounted for is water.

The researchers propose that water ice particles scattered about on the Moon may briefly turn to water when impacted by the dust and debris that routinely slam into its surface. The timing of this marriage of iron, water, and oxygen would have to be perfect, but it’s possible that this is the source of the Moon’s rust.

In the future, crewed missions to the surface of the Moon may be able to weigh in on this hypothesis and either prove or disprove it based on their own observations and data collection.