September 28, 2010
Figure 1: Spatial variation of the energetic neutral hydrogen flux over the magnetic anomaly close to the Gerasimovic crater. (a) High energy hydrogen flux with energy indicates a ~50% flux reduction inside the magnetic anomaly compared to the surrounding area. (b) Hydrogen flux with lower energy of 30-100 eV fills the magnetic anomaly. (c) The albedo (reflectivity) map of the Moon with the spacecraft trajectories (white lines).
Scientists have discovered a new type of solar wind interaction with airless bodies in our solar system. Magnetized regions called magnetic anomalies, mostly on the far side of the Moon, were found to strongly deflect the solar wind, shielding the Moon’s surface. This will help understand the solar wind behaviour near the lunar surface and how water may be generated in its upper layer. Observational evidence for these findings were presented by Drs. Yoshifumi Futaana and Martin Wieser at the European Planetary Science Congress in Rome, on Friday 24th September.
Atmosphere-less bodies interact with the solar wind quite differently than the Earth: Their surfaces are exposed without any shielding by a dense atmosphere or magnetosphere. This causes them to be heavily weathered by meteoroids or the solar wind, forming a very rough and chaotic surface called regolith. Previously, the solar wind was thought to be completely absorbed by regolith. However, recent explorations of the Earth's moon by the Chang'E-1, Kaguya and Chandrayaan-1 spacecrafts have revealed that this interaction is not that simple.
A significant flux of high energy particles was found to originate from the lunar surface, most probably due to the solar wind directly reflected off the Moon’s regolith. “These results may change dramatically the way we understood the solar wind-regolith interaction so far,” says Dr. Futaana of the Swedish Institute of Space Physics. “Since the solar wind is one potential source of water on the Moon, we need to make better models of the lunar hydrogen circulation in order to understand how water molecules form in its upper layers. Also, it will be possible to remotely investigate the solar wind-surface interaction on other airless bodies, such as Mercury or the Martian moon Phobos, by imaging the energetic hydrogen atoms that are reflected back to space when the solar wind hits their surface,” he adds.
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