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How fast can coronal mass ejections travel?

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Space weather Earth's full North Polar auroral oval, in an image taken in ultraviolet light by the U.S. Polar spacecraft over northern Canada, April 6, 1996. In the colour-coded image, which simultaneously shows dayside and nightside auroral activity, the most intense levels of activity are red, and the lowest levels are blue. Polar, launched in February 1996, was designed to further scientists' understanding of how plasma energy contained in the solar wind interacts with Earth's magnetosphere.

Coronal mass ejections (CMEs) are launched from the Sun's outer atmosphere at a wide variety of speeds. These eruptions of magnetized plasma can travel at velocities ranging from less than 10 km (6 miles) per second to more than 2,000 km (1,200 miles) per second.12

CMEs that travel faster than the background solar wind—which typically moves at an average speed of about 400 km (240 miles) per second—are classified as fast CMEs. These high-speed eruptions are particularly significant for space weather, as they are capable of driving interplanetary shocks and triggering intense geomagnetic storms upon reaching Earth.12