First observation of a mini-magnetosphere above a lunar magnetic anomaly using energetic neutral atoms

The Sub‐keV Atom Reflecting Analyzer (SARA) instrument on the Indian Chandrayaan‐1 spacecraft has produced for the first time an image of a lunar magnetic anomaly in backscattered hydrogen atoms. The image shows that a partial void of the solar wind, a mini‐magnetosphere, is formed above the strong magnetic anomaly near the Crisium antipode. The mini‐magnetosphere is 360 km across at the surface and is surrounded by a 300‐km‐thick region of enhanced plasma flux that results from the solar wind flowing around the mini‐magnetosphere. The mini‐magnetosphere is visible only in hydrogen atoms with energy exceeding 150 eV. Fluxes with energies below 100 eV do not show corresponding spatial variations. While the high‐energy atoms result from the backscattering process, the origin of the low‐energy component is puzzling. These observations reveal a new class of objects, mini‐magnetospheres, and demonstrate a new observational technique to study airless bodies, imaging in backscattered neutral atoms.