Billions of tonnes of magnetised plasma are periodically ejected into space by the Sun’s churning convection currents in the upper layers of its atmosphere. These ‘coronal mass ejections’ (CMEs) travel at speeds of up to 11,000,000 kilometres per hour, and the Sun can fire off as many as 20 per week, depending on where it is in its 11-year activity cycle.
Although CMEs are common, they are launched in a narrow arc, and the chances of a large one hitting the Earth are relatively low. We had a near miss in 2012, but the last big strike was in 1859, before society became reliant on electricity.
If a CME on a similar scale was to strike the Earth today, it could damage the electronics in orbiting satellites, disrupting navigation and communications systems, as well as the GPS time synchronisation that the internet relies on to function. It would also create a surge of electromagnetic radiation in the atmosphere, causing huge currents in our power grids which could burn out electrical transformers, leading to length outages.
Without power, society itself would grind to a halt – not just the internet. But this is a worst-case scenario. Scientists monitoring the Sun would be able to give us a couple of days’ warning of a dangerous CME, and in that time, vulnerable satellites could be shut down temporarily, and power grids reconfigured, in order to limit the disruption.