Solar probe untangles riddle of flux ropes
Sen— A NASA space telescope has finally confirmed to solar scientists the processes that produce massive explosions on the Sun. A flare on 18 July, 2012, allowed the Solar Dynamics Observatory to watch the development of a sequence of events that led to a classic eruption termed a Coronal Mass Ejection (CME).
The pattern observed supported a theory that the scientists had long thought to be responsible - the formation of something termed a flux rope as magnetic field lines in the Sun's corona began to twist about, generating a coil of the hottest material on the Sun, a charged gas called plasma.
The flux rope was seen to form following an initial fairly small blast of light spotted off the lower right limb of the Sun. Often such flares are accompanied by CMEs, but this one was not which allowed developments to be observed in detail.
Just eight hours later, on 19 July, there was another flare in the same region and the flux rope's link to the Sun was severed, allowing the magnetic fields to escape into space and the eruption of billions of tons of solar material in a CME.
Though flux ropes have been seen before in images of CMEs blasting away from the Sun, it was hard to make out any detail amongst other structures in the corona. And it has been a matter of fierce debate whether the ropes formed before or in conjunction with a CME's launch. SDO's observation shows clearly that the flux rope formed ahead of the eruption.
UK solar scientist Dr Lucie Green, of the Mullard Space Science Laboratory, told Sen: "I think that it's a great observation. Flux ropes are a fundamental building block of the Sun's magnetised atmosphere and, according to theory and observations of CMEs when they reach the Earth, flux ropes are the key to understanding these eruptions.
"Previously we have seen a few cases of flux ropes forming before they erupt as a CME when looking at them from above. This work is important as it shows a flux rope forming as seen from the side. In this way we can get important information such as how high the rope is in the Sun's atmosphere - something we cannot do when looking at the structure from above."
A NASA video describes the first sightings of how a CME forms. Credit: NASA/Goddard Space Flight Center
Dr Lucie, who has written for Sen on how the Sun causes space weather, added: "Also, the amazing detail, rapid images and ability to see electrically charged gas, or plasma, at different temperatures means that SDO is giving us a new view of flux rope formation and eruption. We see the formation in detail that hasn't been possible before."
Angelos Vourlidas, a solar scientist at the Naval Research Laboratory in Washington, D.C. said: "Seeing this structure was amazing. It looks exactly like the cartoon sketches theorists have been drawing of flux ropes since the 1970s. It was a series of figure eights lined up to look like a giant slinky on the Sun."
The scientists were aided in their discovery by two other Sun probes, NASA's widely separated twins the Solar Terrestrial Relations Observatory (STEREO) which orbit the Sun ahead of and behind the Earth. These viewed from different perspectives with STEREO-A giving a top-down view of the flux rope which helped unravel its 3D structure.
An impression of the Solar Dynamics Observatory watching the Sun. Credit: NASA
The observations are important because understanding just how a CME forms will help space scientists eventually to predict solar storms that can threaten astronauts or wreak havoc with satellite electronics and power grids.
Dean Pesnell, SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said: "By telling us when and where flux ropes will erupt, SDO helps us predict a major source of space weather."