The Earth’s magnetic field, shaped by the solar wind
One of the significant finds coming from India’s first lunar orbiter, Chandrayaan-1, was the detection of hydrogen in many places across the entire lunar surface, in places where it seemed impossible for hydrogen to be there, even if it was locked in a molecule like water.
Researchers in Hawaii now think they have found an explanation by linking that data to the Earth’s long magnetotail, formed by the solar wind pushing against the Earth’s magnetic field. The graphic to the right illustrates that process. The scientists focused on the kind of weathering processes that occurred both when the Moon was inside that tail, and when it was not.
Li and co-authors analyzed the remote sensing data that were collected by the Moon Mineralogy Mapper instrument onboard India’s Chandrayaan 1 mission between 2008 and 2009. Specifically, they assessed the changes in water formation as the Moon traversed through Earth’s magnetotail, which includes the plasma sheet.
“To my surprise, the remote sensing observations showed that the water formation in Earth’s magnetotail is almost identical to the time when the Moon was outside of the Earth’s magnetotail,” said Li. “This indicates that, in the magnetotail, there may be additional formation processes or new sources of water not directly associated with the implantation of solar wind protons. In particular, radiation by high energy electrons exhibits similar effects as the solar wind protons.”
In other words, the evidence suggests that the hydrogen signal seen by Chandrayaan-1 might have been a very temporary implacement of that hydrogen by the solar wind, which ceases during the Moon’s periodic passages through the magnetotail. The Moon’s harsh environment then causes that hydrogen to vanish, only to reappear when it is once again exposed to the solar wind.
None of this is confirmed, so some skepticism is required. If true, however, it would provide further evidence that the hydrogen signal seen at the lunar poles that scientists hope is evidence of ice in the permanently shadowed craters might be nothing of the sort, and we shall find little ice there.
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