New research indicates that planet Earth has been providing the moon with oxygen for at least 2.4 billion years. Throughout the period, approximately 4 trillion trillion trillion oxygen atoms have become embedded in the lunar soil.
Oxygen is leaving our atmosphere
Air is continuously leaving our atmosphere and heading into space, simply because some atoms and molecules located at the top of the atmosphere move so fast that they overcome the planet’s gravitational thug and escape. For each 24 hour period, an average of 90 metric tons of air leave the atmosphere this way.
Charged particles are known to be accelerated to very high speeds by Earth’s magnetic field. When these rapidly moving particles leaves the atmosphere they don’t just wander out into space haphazardly – they are held within the Earth’s magnetosphere.
Earth’s magnetosphere is the region above the ionosphere that is defined by the extent of the Earth’s magnetic field in space. Earth’s magnetosphere extends several tens of thousands of kilometres into space and protects our planet from charged particles that would otherwise strip away our upper atmosphere (including our ozone layer).
Earth’s magnetosphere shields the moon for dive days a month
During a majority of each month, the moon gets bombarded with highly charged atoms from the sun. (These particles are brought to the moon from the sun by the solar wind.)
But five days a month are different, because during these five days Earth’s magnetosphere is located between the moon and the sun, shielding the moon from the solar particles. During these five days, slower speed particles from planet Earth reach the moon instead.
The interesting findings onboard the Kaguya moon-orbiting probe
In 2008, sensors on Japan’s Kaguya moon-orbiting probe detected something interesting. During a small part of each month, there was a dramatic change in what kinds of oxygen ions that reached the craft. These ions moved slower and had just a single positive charge – very different from the ions normally carried to the craft by the solar wind.
Further investigation revealed that this change always occurred within the five day period when the solar wind was blocked by Earth’s magnetosphere.
These factors led researchers at Osaka University in Toyonaka, Japan to suggest that the oxygen ions hailed from Earth.
The oxygen is coming from Earth’s ozone layer, says Japanese researchers
According to research carried out by a team headed by cosmochemist Kentaro Terada at Osaka University in Toyonaka, Japan, an estimated 26,000 ions passed through each square centimetre of the sensor during each burst of oxygen.
The team now suggest that the earthly oxygen deposited on the moon comes from the Earth’s ozone layer. Ozone (trioxygen) is a molecule consisting of three oxygen atoms. Certain wavelengths of sunlight are capable of breaking up this molecule into one single oxygen atom and a molecule consisting of two oxygen atoms (dioxygen). The single oxygen atoms will then filter up towards the top of the atmosphere, from where they can continue to journey into space and eventually end up on the moon.
If the oxygen on the moon comes from Earth’s ozone layers, that might help explain something that has been puzzling the scientific community since Apollo astronauts first brought back soil samples from the moon. When these samples were analysed, a few of the grains showed surprisingly high levels of oxygen-17 and oxygen-18 isotopes. This was unexpected, since it is generally assumed that the known universe’s overall supply of oxygen is dominated by oxygen-16. In Earth’s ozone layer however, the overall proportions of oxygen isotopes are skewed towards oxygen-17 and oxygen-18.
Nature Astronomy 1, Article number: 0026 (2017)
Published online 30 January 2017
- Kentaro Terada
- Shoichiro Yokota
- Yoshifumi Saito
- Naritoshi Kitamura
- Kazushi Asamura
- Masaki N. Nishino