PerspectivePlanetary Science

Magnetic Twisters on Mercury

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Science  01 May 2009:
Vol. 324, Issue 5927, pp. 597-598
DOI: 10.1126/science.1173770

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Mercury is an enigmatic planet. Located closest to the Sun and without an atmosphere, it has only a weak planetary magnetic field to help it withstand the solar wind. The recent flybys of the MESSENGER spacecraft confirm the existence of the Hermean magnetosphere (1, 2), discovered 35 years ago by the Mariner 10 mission (3). This magnetosphere is rather small, with the magnetopause (the boundary between the interplanetary medium and the magnetospheric plasma) located as close as 1700 km above the planet surface. Not much is known about the structure and dynamics of the Hermean magnetosphere, and it is here where the observations by MESSENGER are shedding new light. Reports on the discovery of magnesium in the exosphere of Mercury by McClintock et al. on page 610 of this issue (4) and the detection of flux transfer events by Slavin et al. on page 606 (2) demonstrate that Mercury is directly exposed to the harsh conditions of the interplanetary medium.