NASA SDO Image: Heart of space weather observed in action

An overlap of data from two NASA spacecraft confirms a sighting of magnetic reconnection on the sun, a process of realigning magnetic fields that lies at the heart of space weather. 

The teal image, from SDO, shows the shape of magnetic field lines in the sun's atmosphere. 

The RHESSI data is in orange. 

Credit: NASA/SDO/RHESSI/Goddard

Two NASA spacecraft have provided the most comprehensive movie ever of a mysterious process at the heart of all explosions on the sun: magnetic reconnection.

Magnetic reconnection happens when magnetic field lines come together, break apart and then exchange partners, snapping into new positions and releasing a jolt of magnetic energy.

This process lies at the heart of giant explosions on the sun, such as solar flares and coronal mass ejections, which can fling radiation and particles across the solar system.

Scientists want to better understand this process so they can provide advance warning of such space weather, which can affect satellites near Earth and interfere with radio communications.

One reason why it's so hard to study is that magnetic reconnection can't be witnessed directly, because magnetic fields are invisible. Instead, scientists use a combination of computer modeling and a scant sampling of observations around magnetic reconnection events to attempt to understand what's going on.

"The community is still trying to understand how magnetic reconnection causes flares," said Yang Su, a solar scientist at the University of Graz in Austria. "We have so many pieces of evidence, but the picture is not yet complete."

Now Su has added a new piece of visual evidence. When searching through observations from NASA's SDO, Solar Dynamics Observatory, Su saw something particularly hard to pull from the data: direct images of magnetic reconnection as it was happening on the sun.

Su and his colleagues reported on these results in Nature Physics on July 14, 2013.

While a few tantalizing images of reconnection have been seen before, this paper shows the first comprehensive set of data that can be used to constrain and improve models of this fundamental process on the sun.

Magnetic field lines, themselves, are indeed invisible, but they naturally force charged particles – the material, called plasma, which makes up the sun – to course along their length.

Space telescopes can see that material appearing as bright lines looping and arcing through the sun's atmosphere, and so map out the presence of magnetic field lines.

Looking at a series of images, Su saw two bundles of field lines move toward each other, meet briefly to form what appeared to be an "X" and then shoot apart with one set of lines and its attendant particles leaping into space and one set falling back down onto the sun.

"This is the first time we've seen the entire, detailed structure of this process, because of the high quality data from SDO," Su said. "It supports the whole picture of reconnection, with visual evidence."

Su said that with these images they could make estimates as to how quickly the magnetic fields reconnected, as well as how much material goes into the process and how much comes out.

Such information can be plugged into magnetic reconnection models to help refine theories about the process.