STEREO-A’s lone encounter rewrites what a Carrington-scale solar storm would do to Earth

NASA’s STEREO-A happened to sit in the direct path of the July 2012 Carrington-class CME, taking the full hit while Earth avoided a direct strike. The spacecraft’s instruments recorded unprecedented in-situ measurements of magnetic fields, plasma density, and shock structure, creating a canonical dataset for extreme solar storms. Analyses using that data suggest a direct Carrington-type event could drive geomagnetic disturbances powerful enough to damage hundreds of high-voltage transformers across North America and Europe, underscoring the value of even hours of warning. The event also anchors statistical risk estimates (roughly 10–15% per decade) and confirms that a future Earth-directed storm could have devastating consequences if not anticipated.