The Moon may be liberally sprinkled with oxygen created by life on Earth, according to new research published Monday in Nature Astronomy. This opens up the possibility that "the Earth's atmosphere of billions of years ago may be preserved on the present-day lunar surface," in the words of the paper's authors, led by Osaka University planetary scientist Kentaro Terada.
The notion that Earth has been periodically sneezing its sky stuff on the Moon, spraying it with the exhalations of now-extinct lifeforms, is not entirely new. Previous teams have suggested that nitrogen and noble gases embedded in the Moon's soil originated on Earth.
But Terada and his co-authors are the first to present evidence that oxygen, an essential ingredient and byproduct of terrestrial life, is regularly peppered all over the Moon's surface.
The team used data collected by the Japanese Kaguya spacecraft in 2008 to show that Earth-brand oxygen ions can make this giant leap during a special five day period in the satellite's orbit, when Earth is located between the Sun and the Moon.
During this time, Earth's magnetic plasma sheet protects the Moon from the bombardment of the solar wind, which is a powerful stream of charged particles emitted by the Sun. But our planet's magnetosphere is filled with its own homegrown energetic particles, and the Kaguya orbiter's Ion Energy Analyzer (IEA) and the Ion Mass Analyzer (IMA) detected them during those five-day breaks from the onslaught of the solar wind.
"Even when the geomagnetic field was less developed or absent in ancient times, the Earth's plasma sheets could have existed and led to effective transportation from the Earth's atmosphere to the lunar surface," Terada's team reported. "This mechanism would be enhanced if the distance between the Earth and the Moon was much smaller than today, as it seems it was. A consequence of this finding is that the entire lunar surface can be contaminated with biogenic terrestrial oxygen, which has been produced by photosynthesis over a few billion years."
If that makes you want to hop on over Moonside in order to excavate the untapped respiratory history of life on Earth, you are not alone (and fortunately, the Moon is becoming a popular destination for landers again).
READ MORE: The Other First Moon Landing
But the paper's authors warn that it will be extremely challenging to differentiate between the ions embedded into the lunar soil by the solar wind, and those that came from Earth.
"It is the accumulated oxygen over billions years of both the solar wind and the Earth wind that the lunar soil preserves," Terada told me over email. "To decipher the accumulated oxygen, we need to distinguish which one is recent, and which one is ancient, even in the single grains."
In other words, it's not as if the lunar soil's oxygen ions come with a clear timestamp, or a paper trail about their origins. But Terada said that drilling into the Moon for a deeper core sample, representing older layers of regolith beneath the surface, might help solve the mystery.
In the meantime, however, Terada's strategy is to look to other worlds for analogous processes. "Very recently, NASA's MAVEN mission reported that even non-magnetic Mars also has plasma sheets," he told me. "So, we predict that ancient Mars' atmosphere is preserved in [the Martian moon] Phobos' soil."
"I believe that the JAXA Phobos mission in the near future will prove this hypothesis," he said. This mission is called Martian Moons eXploration (MMX), and is scheduled to launch to Phobos in 2022, where it will collect samples of the moon to be returned to Earth.
So, there you have it: Earth and Mars may have stashed valuable deposits of information about their atmospheric pasts into the soil of their natural satellites. That's should give you a premium bump of Sagan-level scientific wonder to start off your week.
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