Courtesy SOHO/LASCO (ESA & NASA)
Early in the morning of October 28, the space-based Solar and Heliospheric Observatory recorded an enormous mass of plasma erupting from the surface of the sun and heading almost directly toward Earth. The titanic explosion, which occurred above a short-lived solar magnetic tempest known as sunspot 10486, produced the third most powerful solar X-ray flare ever detected. Within seconds, our planet was bombarded with a flood of intense radiation, which ionized the upper layers of the atmosphere and disrupted radio communication. Immediately after, Earth was pounded by a storm of high-energy protons that interfered with the electronic components of satellites, although no serious damage was reported.
The explosion blew off a coronal mass ejection—a vast bubble of electrified gas, or plasma—that quickly expanded to more than 10 times the diameter of the sun. The solar plasma raced toward Earth at 4.6 million miles per hour, five times faster than a normal coronal mass ejection. The blast hit Earth’s atmosphere at approximately 1 a.m. EST on October 29, triggering a category G5 geomagnetic storm, the most intense on atmospheric scientists’ scales. The resulting twists and turns of Earth’s magnetic field disrupted airline communication, endangered satellites, threatened power grids, and increased auroral activity.
The solar flare, seen here in images snapped by telescopes aboard the Solar and Heliospheric Observatory, was categorized as an X17.2 explosion. Solar flares are grouped into three classes, X, M, and C, based on their intensity, and then further subdivided, for example from X1 to X20. X-class flares are the powerful ones, capable of releasing as much energy as a billion megatons of TNT and causing planet-wide radio blackouts and long-lasting radio storms. The largest solar flare on record, an X20, occurred on April 2, 2001, but it was hurled off the limb of the sun away from Earth and so did no damage. The second largest, which erupted on August 16, 1989, and also initiated a level G5 geomagnetic storm, shut down the power grid in Quebec, Canada, leading to widespread electrical blackouts.
Solar turmoil continued on later on October 29. A category X10 solar flare, one of the top 10 most powerful on record, erupted at 3:37 p.m. EST and hurled another coronal mass ejection directly toward Earth. It hit the atmosphere around 10 a.m. EST on October 30.