A coronal mass ejection is a significant release of plasma and magnetic field from the Sun’s corona into the heliosphere.
These ejections are often linked to solar flares and other solar activity, though the precise relationships remain incompletely understood. When a coronal mass ejection enters interplanetary space it becomes an interplanetary coronal mass ejection, capable of reaching Earth’s magnetosphere and triggering geomagnetic storms, auroral displays and, in rare cases, damage to electrical infrastructure. The largest recorded event was the solar storm of 1859 — the Carrington Event — which disabled sections of the United States telegraph network, igniting fires and shocking operators. The frequency of coronal mass ejections follows the Sun’s eleven-year cycle: near solar maxima the Sun produces roughly three per day, dropping to one every five days near solar minima. These plasma bursts shape space weather and pose a persistent challenge for satellite operations, power grids and high-latitude navigation.
Coronal mass ejections feature in our Field Notes coverage of environmental science and global change.
