Coronal Mass Ejections: The Billion-Tonne Plasma Bursts That Knock Out Satellites and Power Grids

The largest thing the Sun ever throws is not light. It is a coronal mass ejection, a bubble of magnetised plasma torn from the Sun's outer atmosphere and flung into the solar system at speeds ranging from 250 to 3,000 kilometres per second. A single ejection can carry more than a billion tonnes of charged particles. For context, that is roughly the combined mass of every ship ever built by humanity, moving fast enough to cross the distance between the Earth and the Moon in under ten minutes.

These events originate in the corona, the Sun's outermost atmospheric layer, where magnetic field lines can become so tangled and stressed that they snap and reconnect violently, a process called magnetic reconnection. The energy released in that snap is what launches the plasma cloud outward. The Sun produces anywhere from one coronal mass ejection every few days during its quieter periods to several per day near the peak of its roughly 11-year activity cycle. The Sun entered Solar Cycle 25 around 2019 and has been climbing toward its maximum, which means ejection frequency has been rising.

Not every ejection hits Earth. The Sun fires them in all directions, and most miss. But when one is aimed at us, it takes between one and three days to travel the 150 million kilometres of the journey. Earth's magnetic field, the magnetosphere, acts as the first line of defence, deflecting the bulk of the charged particles around the planet. The problem is what happens at the seams.

When the magnetic field embedded in the incoming plasma is oriented opposite to Earth's own field, the two fields partially cancel each other. This allows charged particles to pour into the magnetosphere in enormous quantities, triggering what scientists call a geomagnetic storm. The storm is measured on the Kp index, a scale from 0 to 9. A Kp of 5 is a minor storm. The Carrington Event of 1859, the most powerful geomagnetic storm in recorded history, would have scored close to a 9. It set telegraph wires on fire across Europe and North America. Operators reported receiving shocks from their equipment even after disconnecting the batteries, because the geomagnetically induced currents in the ground were strong enough to power the lines on their own.

A Carrington-scale event today would not burn telegraph wires. It would burn transformer cores inside high-voltage power substations. A 2008 report by the US National Academy of Sciences estimated that a storm of that magnitude could cause $1 to $2 trillion in damage in the United States alone and leave parts of the country without power for months, because the specialised transformers that would fail are manufactured in small numbers and take up to two years to replace.

The damage begins well before any current reaches the ground. During a geomagnetic storm, the upper atmosphere heats up and expands outward. Satellites in low Earth orbit suddenly find themselves pushing through denser air than their orbital calculations assumed, which increases drag and causes them to lose altitude faster than expected. The European Space Agency's Swarm constellation and dozens of other satellites had to perform unplanned manoeuvres after a series of strong solar storms in 2024.

GPS accuracy degrades during storms because the charged particles in the ionosphere, the layer of atmosphere between roughly 60 and 1,000 kilometres altitude, alter the speed at which GPS signals travel. A signal that normally takes a precisely known time to reach your phone arrives slightly late, and the receiver interprets that delay as distance. During a strong storm, GPS positioning errors can reach tens of metres, which is catastrophic for aircraft navigation, precision agriculture, and the timing systems that synchronise financial transactions and mobile networks.

Radio communications, particularly high-frequency bands used by aviation and maritime sectors, can black out entirely when a solar flare accompanies the ejection. The flare travels at the speed of light and arrives at Earth eight minutes after leaving the Sun, long before the plasma cloud does. This X-ray burst ionises the sunlit side of the ionosphere and absorbs radio signals, creating what is called a shortwave fadeout. Airlines flying polar routes, which pass through regions where the magnetic shielding is thinnest, are the most exposed.

India's solar observatory, Aditya-L1, was launched by ISRO in September 2023 and reached its operational position at the Sun-Earth Lagrange Point 1, about 1.5 million kilometres from Earth, in January 2024. From there, it has an unobstructed view of the Sun and sits far enough upstream in the solar wind to give Earth roughly an hour's warning before an incoming plasma cloud arrives. The spacecraft carries seven payloads, including the Solar Wind Particle Experiment and the Magnetometer, both designed to measure exactly the kind of conditions that precede and accompany a coronal mass ejection.

Aditya-L1 joins a network of spacecraft that includes NASA's Advanced Composition Explorer, which has been monitoring the solar wind from the same Lagrange point since 1997, and the Parker Solar Probe, which has been flying closer to the Sun than any previous spacecraft, passing through the corona itself in 2021, to study the mechanisms that accelerate solar wind and launch these ejections. The data from these missions feeds into space weather forecasting centres, including NOAA's Space Weather Prediction Center in the United States and the Indian Institute of Geomagnetism in Mumbai, which issue alerts to satellite operators, power grid managers, and aviation authorities.

The May 2024 geomagnetic storm, the strongest in about two decades, reaching G5 on NOAA's geomagnetic storm scale, produced auroras visible across northern India, including reports from Ladakh and parts of Himachal Pradesh. It also caused GPS disruptions and triggered protective shutdowns on some power grid equipment in North America and Europe. ISRO's Aditya-L1 was operational during the event and collected data on the multiple coronal mass ejections that caused it.

Space weather forecasting has improved substantially, but the warning window remains narrow. One hour of advance notice is enough to put a satellite into a protective safe mode. It is not enough to cold-start a national grid response. Power utilities in countries with mature space weather programmes, the United States, the United Kingdom, Sweden, have begun installing geomagnetically induced current monitors on transformer networks and running drills for storm scenarios. India's grid, which carries power across one of the largest and most complex interconnected systems in the world, is in earlier stages of this kind of hardening.

The Sun does not announce which ejection will be the large one. The Carrington Event was preceded by a smaller storm that had partially cleared the path through the solar wind, allowing the second, larger ejection to travel faster than it would have otherwise. That sequence, a clearing storm followed by a faster, more damaging one, is now called a cannibal coronal mass ejection, and forecasters watch for it specifically.

The billion tonnes of plasma the Sun threw in 1859 arrived at a world with copper telegraph wire and no satellites. The same mass, moving at the same speed, aimed at the same planet now, would find a civilisation that has built its navigation, communication, finance, and power distribution on systems that treat a stable electromagnetic environment as a permanent given. The storm does not change. The exposure does.