What are Coronal Mass Ejections?

Coronal mass ejections, or CME’s, are huge bubbles of plasma with embedded magnetic fields that are ejected from the surface of the Sun [1]. These CME’s contain billions of tons of coronal material and can travel as fast as 3000 km/s (1% the speed of light) as they expand and shoot through space. These are among the most powerful explosions in our solar system, along with solar flares, which erupt with the power of 20 million nuclear bombs. Solar flares and CME’s are often associated with each other as they sometimes occur together, however there has been no definitive relationship established between the two phenomena [2].

The cause of coronal mass ejections is not fully understood, however most scientists agree that the main cause is due to fluctuations in the Suns magnetic field [3]. As the Sun is fluid and is affected by turbulence, its magnetic field can become tangled and kinked which can catapult huge amounts matter out into space. As CME’s are ejected in all directions, most of them are not aimed directly towards us, but occasionally they do impact Earth. The frequency of CME’s vary with the activity of the Sun, which changes over an 11 year period [4]. At periods of high activity (solar maxima) the size and recurrence of CME’s increases, which can have huge effects for us on Earth.

CME’s and the Northern Lights

The Earth’s magnetosphere shields the planet from harmful solar particles such as those produced in CME’s and prevents the erosion of the atmosphere by the continuous flow of charged particles from the Sun, known as the solar wind. Because of the constant bombardment of the magnetosphere by this solar weather, it is compressed on the side facing the Sun and extends into a long tail on the dark side of the Earth [5]. Some of the charged particles can reach the Earth’s atmosphere at the poles, guided by Earth’s magnetic field lines, and interact with oxygen and nitrogen in the upper atmosphere. These interactions produce the commonly known phenomenon of aurorae, which typically form 80 to 500km above the surface [6]. Large coronal mass ejections that reach Earth can create major geomagnetic storms and cause these amazing aurorae to expand away from the poles towards the equator.


Image taken by ESA astronaut Alexander Gerst of aurora from the International Space Station on Aug. 29, 2014. Image Credit: NASA/ESA/Alexander Gerst

How would a large CME affect Earth?

A particularly large CME could have major consequences for us on Earth, especially in relation to technology. The potentially huge disruption to Earth’s magnetic field could induce electric currents causing power surges, which could blow out transformers and cripple the electrical grid. Although the Earth’s atmosphere protects us from the dangerous radiation that accompanies them, unprotected astronauts in space would be at a much greater risk.  Furthermore the electronics onboard satellites in orbit could be damaged, causing huge disruptions to communications networks and GPS systems. This would effectively halt the transportation network due to the complete shutdown of air traffic communications. The largest recorded solar storm occurred in 1859, known as the Carrington Event [7]. This storm induced huge currents in electrical circuits, leaving many telegraph lines in North America inoperable. The storm also caused aurorae to be seen as far south as Hawaii and the Caribbean.

Studying Solar Activity

Due to the huge risk that coronal mass ejections pose to the way of life of our modern, technology-dependent civilisation, astronomers study the Sun in order to be more prepared for a large solar event. An impending coronal mass ejection impact can be spotted using a special type of telescope called a coronagraph. The coronagraph blocks out the main bright light of the Sun using a circular shade called an occulting disk. This allows the weaker detail of the corona to be observed. CME’s that are directed towards Earth are called halo events and can be observed using these coronagraphs, which could provide us with the necessary time to plan shutdowns to protect essential communications networks and the electrical grid. Halo events get their name from their appearance, as the ejected coronal matter appears to surround the Sun like a halo as it approaches Earth. Halo event coronal mass ejections usually reach Earth in around two to four days, giving time for scientists to plan an appropriate response.


Illustration of CME in the direction of Earth. The blue lines illustrate the arrangement of earths magnetic field as a consequence of solar weather. Image credit: ESA

In summary, large CME’s have the potential to wreak havoc on our modern technology by affecting communication networks and electrical circuits which have far-reaching effects in all aspects of life. As we approach the next expected solar maximum in 2025, with the predicted increase in solar activity and the frequency of CME’s, it is important for us as a civilisation to watch this Space…


Written by Thomas Jones.


[1]. The Heliopedia. NASA. (2022). Retrieved 11 May 2022, from https://www.nasa.gov/mission_pages/sunearth/the-heliopedia.

[2]. Coronal mass ejection – Wikipedia. En.wikipedia.org. (2022). Retrieved 11 May 2022, from https://en.wikipedia.org/wiki/Coronal_mass_ejection.

[3]. Coronal Mass Ejections | NOAA / NWS Space Weather Prediction Center. Swpc.noaa.gov. (2022). Retrieved 11 May 2022, from https://www.swpc.noaa.gov/phenomena/coronal-mass-ejections.

[4]. What Is the Solar Cycle? | NASA Space Place – NASA Science for Kids. Spaceplace.nasa.gov. (2022). Retrieved 11 May 2022, from https://spaceplace.nasa.gov/solar-cycles/en/.

[5]. Crockett, C. (2022). What is a coronal mass ejection? | Space | EarthSky. EarthSky | Updates on your cosmos and world. Retrieved 11 May 2022, from https://earthsky.org/space/what-are-coronal-mass-ejections/.

[6]. Aurora | NOAA / NWS Space Weather Prediction Center. Swpc.noaa.gov. (2022). Retrieved 11 May 2022, from https://www.swpc.noaa.gov/phenomena/aurora.

[7]. Klein, C. (2022). A Perfect Solar Superstorm: The 1859 Carrington Event. HISTORY. Retrieved 11 May 2022, from https://www.history.com/news/a-perfect-solar-superstorm-the-1859-carrington-event.

[8] Space Weather Research Explorer: CMEs. Exploratorium.edu. (2022). Retrieved 11 May 2022, from https://www.exploratorium.edu/spaceweather/cme.html.



1 reply

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply