'Slinky' magnetic loops seen on Sun

Magnetic arcade: Like a coiled spring on the Sun's surface

By BBC News Online science editor Dr David Whitehouse

On 14 July, an active region on the Sun's surface, designated AR9077, erupted in one of the most energetic flares seen on the surface of our star for years.

Superhot gas and magnetic fields mingle over an the active region

As a result of the explosion, a cloud of energetic charged particles was ejected towards Earth, triggering a geomagnetic storm and displays of aurorae.

Watching the site of the explosion on the Sun was Nasa's Trace satellite. Its cameras took a remarkable close-up of AR9077 just after the flare erupted.

Taken in ultra-violet light, the image shows multi-million degree hot plasma cooling down while supported in an arcade of magnetic loops. Each magnetic loop is far larger than the diameter of the Earth.

Trace monitors the Sun from Earth orbit

Active regions on the Sun's surface are caused by magnetic fields, in the form of gigantic tubes, that rise-up from below the visible surface. When they do so, they become filled with superhot gas that highlights their loops and coils.

Because the magnetic loops are twisted, they eventually buckle and reconfigure their shape, liberating vast amounts of energy that explosively heats gas and expels some of it into space.

Trace's instruments have been designed to look at the magnetic structures on the Sun's surface and follow their changes as flares develop.