A large solar prominence, recorded by SOHO

A solar prominence is a large bright feature located in the solar corona. While the corona consists of extremely hot gases which do not emit much visible light, prominences contain much cooler gas, similar in composition to that of the chromosphere. A prominence forms over timescales of about a day, and may persist in the corona for several weeks. Many prominences break apart and give rise to coronal mass ejections.

Despite decades of study, the mechanism by which prominences form is not yet well understood. Theories have not satisfactorily explained how prominences can remain stable for such a long time when they are much denser than their surroundings. Magnetic fields are known to be the dominant influence on gas motions within the corona, but the exact form of magnetic interaction required to produce and maintain a large prominence has yet to be determined.

A typical prominence extends over many thousands of miles; the largest observed by SOHO was seen in 1997 and was some 200,000 miles long - some 27 times the radius of the Earth. The mass contained within a prominence is typically of the order of 100 billion tonnes of material.

References

1. Galsgaard K., Longbottom A.W. (1999), Formation of solar prominences by flux convergence, Astrophysical Journal, v.510, p.444
2. Low, B.C. Fong, B.; Fan, Y. (2003), The mass of a solar quiescent prominence, Astrophysical Journal, v.594, p. 1060