Our cosmic homeland has a precious protective shield: The earth's magnetic field largely protects us from the stream of charged particles, which emanates constantly from the sun. This so-called solar wind consists mainly of ionized hydrogen, but also contains traces of other charged elements - including oxygen ions. In contrast to the earth, the particles of the solar wind normally bounce unhindered on the moon - but in five days of its orbital period this is not the case: When the earth lies between the moon and the sun, our Trabant is as it were in the lee of the magnetic field of the earth, whereby it is also shielded from the sun's particle radiation.
Oxygen shower in the lee of the earth
At this stage, ions can flow from the earth to the moon, as evidenced by earlier studies of lunar soil: Certain isotopic compositions of nitrogen and noble gases suggest that they were originally from Earth to the Moon. Whether charged particles of the oxygen of life reach the moon, however, has so far been unclear due to the ambiguous characteristics of the isotope patterns: the traces in lunar material could also have come from the solar wind. The researchers around Kentaro Terada from Osaka University in Toyonaka have now used another way to track down the possible oxygen flow: They used data from the research probe Kaguya of the Japanese space agency JAXA, which was in orbit from 2007 to 2009 was around the moon.
From the measurement results of certain instruments of the probe was clear: Whenever the moon is shielded by the terrestrial magnetic field from the solar wind, actually reached him also charged oxygen particles of our planet. They separate from the outer layers of the earth's atmosphere and then reach the lunar surface in a kind of earth wind. Due to their high speed, they can penetrate slightly into the surface material of the moon and remain there, the researchers explain.
Traces of earthly life on the moon
According to them, this process has been going on for about 2.5 million years - since the Earth's atmosphere has accumulated significant levels of oxygen. Since most of the Earth's oxygen is a product of life, it means that the Moon has been continuously showered with these traces of life for much of its history. Perhaps this could signify a chronological signature of the development of the biologically dominated earth atmosphere in the lunar soil, the researchers say. display
However, whether this archive can be used to explore the history of the earth remains questionable, say Terada and his colleagues. Presumably, it would be difficult to distinguish the oxygen, which has come through the solar wind on the moon, from the oxygen of the earth's wind, say the scientists. But one thing seems clear: earthly life has even left a mark on the moon.
Original work of the researchers:
- Nature, doi: 10.1038 / s41550-016-0026