© 2019 - All Rights Reserved
|The moon up close as seen by Japan’s Kaguya lunar orbiter. Scientists said the probe detected signs of oxygen that came from Earth and was present on the lunar surface. Credit: JAXA/NHK|
|This diagram shows how the solar wind and Earth’s magnetic field funnel oxygen ions from Earth to the moon. Japan’s Kaguya lunar orbiter detected the oxygen isotope on the moon. Credit: Osaka University/NASA|
Terada told Space.com that the evidence for where the ions came from was the isotope oxygen-16. Earth’s upper atmosphere and the moon have relatively little oxygen-16, whereas the solar wind has more. The lunar soil’s oxygen content has three components: One is rich in oxygen-16, and that is from the solar wind. Another is poor in oxygen-16, and it wasn’t clear where that came from, until the team looked at the data and compared this component to the ions in Earth’s atmosphere.
“Interestingly, the isotopic opposition of the unknown [oxygen-16]-poor component of lunar soil is quite identical to that of ozone layer,” Terada said.
The third feature is that the ions from the sun are more highly charged. Neutral oxygen atoms have eight protons and eight electrons. Oxygen atoms from Earth usually lose only one electron (and are noted as O+). The ones from the sun are often stripped of more electrons than that; they will be O5+, for instance, meaning the atom lost five electrons. A highly ionized solar oxygen atom would be unlikely to duplicate the behavior of a singly ionized atom from Earth, the researchers said, because the ion from the solar wind would have to regain some of the electrons that got stripped off. It’s unlikely that the electrons and the atoms would meet by chance to recombine, the scientists said.
Another piece of evidence that this oxygen came from Earth was how far the ions penetrated into the lunar soil, the scientists said. The ions from Earth fell into the same range as the oxygen ions the team found on the moon: about 1,000 electron volts. Those ions originating from the sun carried much higher energies, and penetrated deeper, the study said.