Coronal Mass Ejection

Coronal mass ejections (or CMEs) are huge bubbles of gas threaded with magnetic field lines that are ejected from the Sun over the course of several hours. Although the Sun's corona has been observed during total eclipses of the Sun for thousands of years, the existence of coronal mass ejections was unrealized until the space age. The earliest evidence of these dynamical events came from observations made with a coronagraph on the 7th Orbiting Solar Observatory (OSO 7) from 1971 to 1973. A coronagraph produces an artificial eclipse of the Sun by placing an "occulting disk" over the image of the Sun. During a natural eclipse of the Sun the corona is only visible for a few minutes at most, too short a period of time to notice any changes in coronal features. With ground based coronagraphs only the innermost corona is visible above the brightness of the sky. From space the corona is visible out to large distances from the Sun and can be viewed continuously. The animated sequence of images at the top of this page were obtained with the High Altitude Observatory's coronagraph on the Solar Maximum Mission in April of 1980.


Magnetic fields in the sun can heat the sun's gases to tens of thousands of degrees. This energy can explode rapidly out of the sun's corona (the unstable outer surface) at very high speeds ejecting up to 10 billion tons of ionised gas into the solar system at speeds of up to 2 million miles per hour.  These events are called coronal mass ejections (CME).  This is different to solar flares because the plasma actually lifts off from and leaves (is ejected from) the surface of the sun.  It is then carried by solar winds into the solar system and can be as big as the sun itself.  A CME can result in magnetic storms when its gasses interact with the Earth's magnetic field.  This distorts the shape of our magnetic field and speeds up the electrically charged particles that are trapped inside.
Coronal mass ejections are often associated with solar flares and prominence eruptions but they can also occur in the absence of either of these processes.

In November 4, 2003 a CME associated with the X28 solar flare, left the sun traveling at 2300 kilometres per second (8.2 million km/h).  It's effect on the planet was minimal because the full blast of the CME was directed away from the earth.