The NASA Jet Propulsion Laboratory at the California Institute of Technology reports that the moon is rusting. Which sounds weird enough on the surface, but gets even stranger when you consider that the moon doesn't have any oxygen or liquid water—the two things typically required to turn iron and iron-rich rocks into rust.
The mystery starts with the solar wind, a stream of charged particles that flows out from the Sun, bombarding Earth and the Moon with hydrogen. Hydrogen makes it harder for hematite to form. It's what is known as a reducer, meaning it adds electrons to the materials it interacts with. That's the opposite of what is needed to make hematite: For iron to rust, it requires an oxidizer, which removes electrons. And while the Earth has a magnetic field shielding it from this hydrogen, the Moon does not.
"It's very puzzling," [Shuai Li of the University of Hawaii] said. "The Moon is a terrible environment for hematite to form in." So he turned to JPL scientists Abigail Fraeman and Vivian Sun to help poke at M3's data and confirm his discovery of hematite.
"At first, I totally didn't believe it. It shouldn't exist based on the conditions present on the Moon," Fraeman said. "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."
After taking a close look, Fraeman and Sun became convinced M3's data does indeed indicate the presence of hematite at the lunar poles. "In the end, the spectra were convincingly hematite-bearing, and there needed to be an explanation for why it's on the Moon," Sun said.
More research is still needed into this strange phenomenon. But right now, their leading theory is that oxygen from Earth can hitch a ride on the planet's own magnetic field—also known, no joke, as a magnetotail—with enough momentum to travel the 239,000 miles to the Moon. It's possible that the oxygen even made the trip billions of years ago, when the Earth and Moon were closer to one another.
The current working theory also posits that the Earth's magnetotail might occasionally block solar wind currents from certain parts of the moon, which would otherwise carry the hydrogen that would prevent the oxidation that leads to rust. And then of course, while there's no known liquid water on the moon—the third piece of the rusting puzzle—there is ice:
Li proposes that fast-moving dust particles that regularly pelt the Moon could release these surface-borne water molecules, mixing them with iron in the lunar soil. Heat from these impacts could increase the oxidation rate; the dust particles themselves may also be carrying water molecules, implanting them into the surface so that they mix with iron. During just the right moments – namely, when the Moon is shielded from the solar wind and oxygen is present – a rust-inducing chemical reaction could occur.
The cosmos are wild.
The Moon Is Rusting, and Researchers Want to Know Why [NASA Jet Propulsion Laboratory / California Institute of Technology]
The Earth is making the moon rust [Jessie Yeung / CNN]
Image: Public Domain via Pixnio
