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Oxygen from Earth’s atmosphere may be traveling all the way to the Moon’s surface

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The byproducts of life are sprinkling onto lunar soil

How oxygen from Earth’s atmosphere may be getting to the Moon
Osaka Univ. / NASA

Despite orbiting nearly 240,000 miles from Earth, our Moon may be periodically mingling with our planet’s atmosphere. New research shows that oxygen from Earth could be journeying all the way out to the Moon, where it then gets lodged inside the lunar soil. It’s a process that’s likely been happening for 2.4 billion years, ever since oxygen formed around our planet, meaning the Moon’s soil may contain trapped particles from Earth’s ancient atmosphere.

This oxygen exchange, detailed in a study published today in Nature Astronomy, supposedly occurs for just a few days during the Moon’s 27-day orbit. Most of the time, the Moon is constantly being blasted with solar wind — fast streams of charged particles emanating from the Sun. But for five days of every lunar orbit, the Moon passes into Earth’s magnetotail, the portion of the planet’s magnetic field that stretches outward away from the Sun. This tail shields the Moon from the solar wind, and allows charged oxygen ions from Earth to travel to the lunar surface, according to the study.

That means the Moon — a dead rock incapable of supporting life — is being showered with the byproducts of life here on Earth. In fact, the source of most of the oxygen in our atmosphere is biological, created by plants during photosynthesis. “Such biogenic oxygens have ... contaminated the lunar surface,” Kentaro Terada, an astrophysicist at Osaka University, tells The Verge.

It’s a process that experts have suspected for a while but haven’t been able to confirm until today. Researchers have also suggested that other atmospheric components, such as nitrogen and noble gases, are getting to the Moon this way based on lunar soil samples. Terada and his team were able to figure out this exchange was happening for oxygen after looking over data collected by the Japanese SELENE lunar orbiter. Launched in 2007, the spacecraft — nicknamed Kaguya — orbited the Moon for a year and eight months to help figure out the evolution and origin of the lunar satellite.

How the Moon passes through the magnetotail of Earth.
Tim Stubbs/University of Maryland/GSFC

The researchers noticed something interesting whenever the Moon and the vehicle passed into Earth’s plasma sheet — a region of hot, charged particles trapped inside the planet’s magnetotail. Kaguya’s plasma detector picked up a significant amount of high-energy oxygen ions. Because these types of ions were only picked up when the Moon was in the plasma sheet, Terada and his team concluded that the oxygen was coming from Earth and not the particles in the solar wind. Some of the oxygen from Earth’s atmosphere may be leaking out into the magnetosphere — the magnetic field bubble that surrounds our planet — where it is heated up and accelerated by electric fields and plasma waves. From there, it’s rapidly transported to the surface of the Moon, the study says.

Given the high energy of the oxygen detected by Kaguya, the researchers believe the ions are capable of lodging into the lunar soil around 100 to 1,000 nanometers in depth. “By simulation, we know that such an ion with high energy can penetrate into the lunar soil,” says Terada. It could help explain why certain oxygen isotopes found inside lunar rocks are identical to isotopes found in the Earth’s ozone layer, according to Terada. However, he and his team argue it may be hard to use lunar samples to study Earth’s atmosphere from eons past, since it’ll be difficult to distinguish the oxygen from the solar wind and the Earth wind in Moon soil.

The Moon is thought to have formed from the leftover debris of a collision between Earth and another Mars-sized object more than 4 billion years ago. And since its formation, the Moon has held physical influence over the Earth, by affecting the ebb and flow of the Earth’s tides and by stabilizing our planet’s rotational axis. Today’s study marks another unique way in which the Earth and the Moon are connected to one another. “The Earth and Moon system have been coevolving not only ‘physically’ but also ‘chemically,’ in spite of the distance,” says Terada.