Three-dimensional images could help to explain solar jets.
The Sun’s violent eruptions may have their origins in tangled magnetic fields that act like a loaded spring, twisting plasma and jettisoning it away.
Solar physicists, debating the mechanism behind these dramatic 'plasma jet' outbursts, have theorized that tangled magnetic fields can contort plasma into a corkscrew shape, forcing the material into space.
Evidence has, however, been hard to come by. "The twisting structure of jets was observed before, but it was not clear whether it was real or an effect of projection of several independent, untwisted structures," says solar physicist Alexander Kosovichev of Stanford University in California.
Now a team studying images from the NASA STEREO spacecraft have captured the first three-dimensional image of a twisting jet of plasma exiting the Sun's pole.
Because these polar jets are produced where the Sun's magnetic field is relatively simple, they may be a good starting point for studying some of the Sun's larger, more complicated eruptions.
“I think these jets might be a Rosetta Stone for understanding all kind of eruptions from the Sun. Spiros Patsurakos , George Mason University”
“I think these jets might be a Rosetta Stone for understanding all kinds of eruptions from the Sun,” says study author Spiros Patsourakos of George Mason University in Fairfax, Virginia. The results were presented at a press conference on Tuesday at a meeting of the American Geophysical Union in Fort Lauderdale, Florida.
The results confirm a model for jet formation developed by coauthor Spiro Antiochos of NASA Goddard Space Flight Center in Greenbelt, Maryland. The model suggests that the jets are created by twisted magnetic fields in the Sun's photosphere, the outer part of the Sun that releases light. The unstable twist will suddenly begin to unravel, blasting out a jet with the tell-tale helical pattern.
First glimpsed in the 1990s by the Japanese solar satellite Yohkoh, the jets are now seen at a rate of several an hour. The relatively small eruptions propel plasma into space at speeds of several hundred kilometres per second and contribute to the Sun's solar wind.
The jets are not related to coronal mass ejections, which blast out large clouds of charged particles and can disrupt power grids and satellites. Such ejections are produced by more complicated magnetic fields at the Sun's lower latitudes. But studying these jets could could help calibrate more complicated models, says Patsourakos.
“I am really happy to see recent progress,” says Kazunari Shibata of Kyoto University, Japan. Shibata says that twist is only one mechanism that might produce jets. Loops of magnetic fields that rise up from the Sun's surface, snap, and reconnect with other stray loops may push out jets like a slingshot. The pressure that causes gases in the Sun to expand may also help create the jets.
"These three mechanisms can occur simultaneously in different events, so of course we have not solved the problem completely,” says Shibata.