Planetary Science

Cracks in the Shield

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Science  06 Jun 2003:
Vol. 300, Issue 5625, pp. 1477
DOI: 10.1126/science.300.5625.1477a

Electrons spiraling down from space (carried by the solar wind) into the atmosphere give rise to colorful curtainlike displays that are seen at high latitudes (aurora borealis in the north and aurora australis in the south), usually at night. Spacecraft-based observations have revealed the existence of daytime or dayside auroras, which are caused by protons, another constituent of the solar wind. It has been suggested that protons can pierce Earth's magnetic shield as a result of energy released by “reconnection” between magnetic field lines in the magnetopause (where Earth's atmosphere and the solar wind meet).

Phan et al. report on simultaneous observations by five satellites that confirm reconnection as the source of dayside auroral emissions. On 18 March 2002, NASA's IMAGE spacecraft recorded a bright dayside auroral spot. At the same time, ESA's CLUSTER mission, which consists of four spacecraft flying in a triangular pyramidal formation, passed through a jet of energetic solar protons that were colliding with Earth's atmosphere, directly above the bright spot. In the future, observations of dayside auroral spots can be used to monitor the formation and mending of cracks in Earth's magnetic shield.—JFU

Geophys. Res. Lett. 30, 1509 (2003).

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