Two NASA spacecraft have provided the most comprehensive video footage ever of a mysterious process that, scientists say, is at the heart of all space weather.
Called magnetic reconnection, it occurs when magnetic field lines come together, break apart and then exchange partners, snapping into new positions and releasing a jolt of magnetic energy. As this happens, radiation and particles are flung across the solar system and giant explosions -- such as solar flares and coronal mass ejections -- occur on the surface of the Sun, .
Despite its widely felt influences, however, little is known regarding magnetic reconnection since magnetic fields are invisible, making it impossible to witness the process directly.
To get around this, scientists use a combination of computer modeling and a scant sampling of observations around the events in order to gather more clues about them.
"The community is still trying to understand how magnetic reconnection causes flares," Yang Su, a solar scientist at the University of Graz in Austria, said in a NASA press release. "We have so many pieces of evidence, but the picture is not yet complete."
Adding to these pieices is new visual evidence of the process Su observed through observations from NASA's Solar Dynamics Observatory: direct images of magnetic reconnection as it occurred on the Sun.
The resulting study, published in the journal Nature Physics, is the first comprehensive set of data that can be used to constrain and improve models of the process, the scientists report.
True, magnetic field lines are invisible, but they naturally force charged particles to course along their length. Space telescopes, in turn, can see that material appearing as bright lines looping and arcing through the Sun's atmosphere, allowing scientists to map out their presence.
By examining 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 accompanying particles leaping into space and one set falling back toward the Sun.
"It can often be hard to tell what's truly happening in three dimensions from these images, since the pictures themselves are two-dimensional," said Gordon Holman, a solar scientist at NASA's Goddard Space Flight Center in Greenbelt, Md., and one of the authors of the paper. "But if you look long enough and compare data from other instruments, you can make a good case for what's going on."
In order to confirm what they thought they were observing, the scientist turned to a second NASA spacecraft, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), which is capable of collecting a kind of data that reveals where exceptionally hot material is present in any given event on the Sun.
RHESSI showed hot pockets of solar material forming above and below the reconnection point, an established signature of such an event. Thus, by combining the SDO and RHESSI data, the scientists were able to describe the process they were seeing. In doing so, they largely confirmed previous models and theories even as they revealed new, three-dimensional aspects of the process.
In short, below the surface of the Sun, the charged material, or plasma, flows and from it magnetic loops emerge, setting up areas of positive magnetic poles next to negative ones. The loops then arc up over the Sun from one polarity to the other and, as the Sun's material continues to flow under the surface, the positive and negative poles slip past each other in a manner similar to Earth's plate tectonics. As a result, the arcs above grow, twist sideways and become more unstable. The very act of that slippage puts more energy into the system, coiled and waiting to spring, like twisting up a rubber band before letting it loose. Eventually, the magnetic field lines in the arcs buckle inward, touch and reconnect while releasing the energy in a bright flash and sending radiation and energetic particles out into space.
In the SDO footage, researchers observed as light illuminated the arcade of loops as the reconnection process cascaded along the length of them. Bright loops leaned into the reconnection region from each side and, as the magnetic field lines reconfigured, new loops were ejected downward while a rope of plasma separated and surged upward. In some cases, the rope achieved escape velocity and became a coronal mass ejection. When this happened, it sent billions of tons of matter out into space.
"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."
Armed with these images, Su believes scientists can now make estimates as to how quickly the magnetic fields reconnected, in addition to how much material goes into the process and how much comes out. Knowing this could help refine theories about the process.
Magnetic reconnection is an intriguing subject for researchers not just because of its role on the Sun, but because it is a universal process, occurring inside the Earth's magnetic environment, the magnetosphere, and in stars everywhere.
For this reason, NASA plans to launch the Magnetospheric Multiscale (MMS) mission in late 2014 in order to study the process in greater detail. The mission consists of four spacecraft that will pass right through magnetic reconnection events where they happen in Earth's magnetosphere.
By bringing multiple spacecraft - SDO, RHESSI, MMS and others - on board, scientists will be able to better understand the very start of the space weather, according to the researchers.