The smallest coronal mass ejection ever observed has caught solar physicists totally by surprise, and reveals just how limited our understanding is of how these eruptions of solar material are generated.

A coronal mass ejection is an explosion inside the sun that ejects a huge quantity of plasma into space. The plasma, composed of highly energetic particles, streams outwards, sometime striking Earth, where it can create stunning Aurorae, interfere with satellites in orbit, and in severe cases, can even knock out electricity supplies.

Normally, these ejections are enormous events, thought to begin in areas of the sun where the magnetic field lines are destabilised into twisted loops which contain a lot of energy. Typically, these areas span millions of square miles of the sun's surface. But researchers have now seen an ejection emerge from an area just 10,000 miles across.

Although the ejection was small, it was energetic enough to reach earth. The international team of astronomers responsible for the discovery says that the magnetic field lines in its area of origin were ten times more twisted than is usually seen in larger areas.

"Previously coronal mass ejections were thought to be huge, involving massive portions of the Sun's magnetic field and all the theoretical models are based around this assumption," commented Mullard Space Science Laboratory's Dr Lucie Green.

"However, this one was amazing in that it came from a tiny magnetic region on the Sun which would normally have been overlooked in the search for CME source regions. This will be an exciting area for further study."

Gaining a decent understanding of how coronal mass ejections are formed is vital to space scientists because they form the basis of space weather. The particles launched into space can wreak havoc, and cause serious harm to astronauts in orbit when they hit, so we need to e able to make good predictions of when they will occur.

Existing models for coronal mass ejections are all based on the large scale event normally observed, and scientists don't know for sure how much of an effect smaller events like this one actually have on space weather. Future missions, such as the planned joint US-UK-Japanese mission Solar B, should shed more light on this area. ®

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