Surface energy ripples up the ‘tree’ trunks and heats the corona, new study suggests!

ENERGY HALO  The solar corona, seen during a 2008 eclipse (colors show emissions from different iron ions), envelops the disk of the sun in this composite image.

Treelike magnetic fields, deeply rooted within the sun and stretching far into its atmosphere, might explain why the solar corona is millions of degrees hotter than the sun’s surface. This swaying forest of magnetic mangroves can carry energy up into the corona thanks to a foaming sea of stronger magnetism close to the surface, researchers report in the June 11 Nature.

The roiling surface of the sun creates a tangled mess of magnetic fields, astrophysicist Tahar Amari of the École Polytechnique in Palaiseau Cedex, France, and colleagues report. Their computer simulations show that these fields twist and break, dumping energy just below the corona, an enormous plasma bubble that envelops the sun. These eruptions in turn rock the weaker mangrovelike fields, which can extend 100,000 kilometers into space and carry the energy the rest of the way to the corona via waves rippling along their trunks.

The sun’s surface simmers at about 5,500° Celsius; the corona, however, is a scorching few million degrees. How the corona gets so hot is a problem that has vexed astronomers for decades.

Recently observed nanoflares within the corona can reach 10 million degrees (SN: 5/30/15, p. 7), but researchers aren’t certain how these flares are generated. Nanoflares could be caused by plasma reacting to movements of the treelike magnetic fields, says Amari, but it’s too early to say for certain.