Recent satellite observations have revealed the largest breach yet seen in the magnetic field that protects Earth from most of the sun's violent blasts. The discovery, made by a fleet of five small NASA satellites known as Themis, was reported at the American Geophysical Union meeting.
Last summer, Themis calculated a layer of solar particles to be at least 4,000 miles thick in the outermost part of the Earth's magnetosphere. Such breaches are temporary, and this one lasted about an hour.
