Science Alert:[2] Our Sun isn’t exactly a serene ball of scorching hot plasma. In fact, it belches out colossal eruptions on a somewhat frequent basis; such coronal mass ejections, when directed at Earth, are the cause of geomagnetic storms.
[3] From near-Earth space, we can measure them pretty well with satellites and other spacecraft.[4] But in 1998 something incredibly fortuitous occurred. Not only was a spacecraft in near-Earth space able to measure a coronal mass ejection (CME), another spacecraft out past Mars lined up in just the right way to also receive the solar blast.
[5] This meant the two spacecraft were able to measure the same CME at different points of its journey from the Sun, offering a rare opportunity to understand how these powerful eruptions evolve. Coronal mass ejections may not be as visible as solar flares (which they sometimes accompany), but they’re much more powerful.

They occur when twisted magnetic field lines on the Sun reconnect, converting and releasing tremendous amounts of energy in the process.

This happens in the form of a CME, in which vast quantities of ionised plasma and electromagnetic radiation, bundled up in a helical magnetic field, are launched into space on the solar wind. When they stream past Earth, CMEs can interact with the magnetosphere and ionosphere, creating observable effects such as satellite communication problems and aurorae.