Earth can raise shields to protect itself against solar storms. For the first time, satellites and ground-based detectors have watched as the planet sends out a tendril of plasma to fight off blasts of charged solar matter. The discovery confirms a long-standing theory about Earth’s magnetic surroundings and offers us a way to keep track of the planet’s defences.
“It’s changed our thinking about how the system operates,” says Joe Borovsky at the Space Science Institute in Boulder, Colorado, who was not involved in the research. “Earth doesn’t just sit there and take whatever the solar wind gives it, it can actually fight back.”
Earth is always surrounded by a bubble of magnetism called the magnetosphere, which protects us from the bulk of the solar wind, a stream of high-energy particles constantly flowing from the sun.
But sometimes, the sun’s magnetic field lines can directly link up with Earth’s in a process called magnetic reconnection, which opens up cracks in the magnetosphere. Charged particles can flow along these lines into Earth’s atmosphere, leading to dazzling auroras as well as geomagnetic storms that can wreak havoc on navigation systems and power grids.