Every so often the sun emits an explosive burst of charged particles that makes its way to Earth and often wreaks havoc on power grids, aircraft and satellite systems. When clouds of high-speed charged particles come racing off the sun, they can bathe spacecraft, astronauts and planetary surfaces in damaging radiation. Understanding why the sun occasionally emits these high-energy particles can help scientists predict space weather. Knowing when solar energetic particles may hit Earth can help people on the planet take precautions.