Over the past decades, we have finally become convinced that the Moon is not at all waterless. Water ice is dispersed in the local soil, hiding in deep darkness at the bottom of the craters. However, its origin here remains a mystery. If water ended up on a satellite after the fall of ice comets, it would quickly evaporate due to the lack of an atmosphere capable of retaining moisture.
Water can appear directly on the moon. According to one of the new promising hypotheses, the solar wind protons reach its surface, which is not protected by either the atmosphere or the magnetosphere, like our Earth. Here they interact with oxides in the composition of minerals, forming new water molecules and constantly replenishing the supply of moisture evaporating into space.
Then, during periods when the Moon is briefly sheltered from the solar wind, the amount of water on its surface should decrease. Computer simulations predict that in a few days around the full moon, as a satellite passes through the long, elongated “tail” of the Earth’s magnetosphere, water content should drop very noticeably at high latitudes.
This process was reviewed by the authors of a new article published in the Astrophysical Journal Letters. Using data collected by the Japanese lunar probe Kaguya, they recorded changes in the flow of the solar wind, “washing” the satellite. And observations of the Indian apparatus Chandrayaan-1 helped to assess the distribution of water in the circumpolar regions. However, the results turned out to be rather unexpected: no significant changes in the amount of ice occur on the prescribed days.
Therefore, scientists put forward another hypothesis for the origin of water on the moon, not related to the effects of the solar wind. The fact is that the Earth’s magnetosphere is also capable of directing protons and watering the lunar surface with no fewer particles than the solar wind: although not so strongly accelerated. The stream contains both protons and oxygen ions from the upper layers of the earth’s atmosphere. This “earth’s wind” may be enough to form new water molecules on the moon.
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