A new study based on data collected by Japan’s Kaguya lunar orbiter confirms that oxygen from Earth’s atmosphere is traveling to the Moon, where it gets trapped in surface rock.
Kaguya was launched in 2007 and orbited the Moon for a year and eight months as part of an effort to trace its history and evolution.
While looking at Kaguya data, a team of researchers discovered that for about five days during the Moon’s orbit around the Earth, the probe’s plasma detector measured a large amount of high-energy oxygen ions approaching the Moon.
Like all other solar system bodies, the Moon is bombarded with streams of charged particles from the Sun, known as the solar wind.
However, during the five days in its monthly orbit when it passes through Earth’s magnetotail, the part of our planet’s magnetic field that extends away from the Sun, the Moon is shielded from the solar wind.
During this time, charged oxygen ions from Earth’s atmosphere are able to travel to the Moon without obstruction.
Significantly, Kayuga’s plasma detector detected high-energy oxygen ions only during the days the Moon passed into Earth’s magnetotail.
Osaka University astrophysicist Kentaro Terada, a member of the research team conducting the study, said he and his colleagues determined the oxygen came from Earth’s atmosphere rather than from particles in the solar wind.
The majority of Earth’s oxygen comes from biological sources, specifically photosynthesis conducted by plants.
Some oxygen from Earth makes its way into the magnetosphere, where electric fields and plasma waves accelerate it and heat it up. It then is easily brought to the Moon.
The energy level of this oxygen detected by the research team was so high that the researchers suspect it is lodging between 100 and 1,000 nanometers into the lunar surface.
“By simulation, we know that such an ion with high energy can penetrate into the lunar soil,” Terada said.
Because oxygen, nitrogen, and other noble gases have been found trapped inside lunar rock samples, scientists long suspected this process was happening but only now have the necessary proof.
Confirmation that oxygen from Earth really is being transported to the Moon could also explain why some oxygen isotopes found in Earth’s ozone layer are identical to those found in Moon rocks.
Transportation of oxygen from the Earth to the Moon has likely been occurring since oxygen formed on Earth, about 2.4 billion years ago, meaning particles from Earth’s ancient atmosphere could still be lurking within lunar soil.
Findings of the study are published in the latest issue of the journal Nature Astronomy.