Magnetic 'Braids' May Cook the Sun
A rocket-propelled solar telescope has revealed a previously unknown fine scale of the sun's corona, potentially exposing an important heating mechanism.
Scientists have long puzzled over why the surface of the sun is cooler than its corona, the outer hazy atmosphere visible during a solar eclipse. Now thanks to a five-minute observation by a small, but very high-resolution ultraviolet telescope they have some answers.
Even before the July 2012 launch of the High-resolution Coronal Imager, nicknamed Hi-C, scientists suspected that magnetic fields on the sun were responsible for ramping up its energy, resulting in a flaring corona that can reach 7 million degrees Fahrenheit, compared to a visible solar surface temperature of about 10,000 degrees.
Hi-C, which was launched aboard a suborbital rocket to study the sun without interference from Earth's atmosphere, revealed interwoven magnetic fields braided like hair. When the braids relaxed, they released energy.
"I had no idea we would see structures like that in the corona. Seeing these braids was very new to me," astrophysicist Jonathan Cirtain with NASA's Marshall Space Flight Center in Huntsville, Ala., told Discovery News.
"Magnetic braiding" is believed to happen when small bundles of magnetic fields become wrapped around each other due to plasma moving around on the sun's surface.
Follow-up observations are needed to learn if the braiding phenomenon is widespread and how important is it to coronal heating.
"Are twisted-up field lines just all over the place? Do they only happen near 'inversion layers,' where you go from a positive net flux out from the sun's surface to negative net flux into the surface? How prevalent is this structure to the overall sun and how important is it to heating the sun's atmosphere? I think that's the next step that we will take," Cirtain said.
"You are not going to solve a problem with five minutes of data," added space scientist and physicist Peter Cargill, with Imperial College London, who isn't associated with this research.
"A rocket flight like this is primarily designed to demonstrate new technology. You hope to get some good science, as they have done, and to point the way toward what to look for when such an instrument flies on a spacecraft," Cargill wrote in an email to Discovery News.
Hi-C had the precision to see the equivalent of something the size of a dime from 10 miles away, allowing astronomers to observe details in extreme ultraviolet light of structures on the sun that were about 100 miles in diameter -- five times better than the resolution of the next-best instrument, the Atmospheric Imaging Assembly aboard NASA's ongoing Solar Dynamics Observatory mission.
The observation was tricky and short. Cirtain said he remotely operated the telescope during flight to home in on a particularly active region of the sun to photograph. The telescope, which was launched from the White Sands Missile Range in New Mexico, then parachuted back to the desert so its onboard data could be recovered and analyzed.
In addition to imaging the small-scale physics of the corona, the research is expected to enrich forecast models for space weather -- a phenomenon that can impact satellites, power girds and other electronics around and on Earth.
"The corona is really the formative location for space weather. If we want to understand how the sun, how stars work in general, that's very important to understand how the universe is put together, but more important in your day-to-day life is the implication space weather has on our technology and our planet. Space weather has economic impacts that haven't been recognized until recently," Cirtain said.
The research is published in this week's Nature.
The Solar Dynamics Observatory (SDO) captured an image (left) of the sun's corona at the time of the Hi-C mission (left). Small-scale magnetic "braids" were uncovered by Hi-C's observation of the 1.5 million degree corona (right).
Living With a Star
Aug. 9, 2011 --
In April 2010, NASA's Solar Dynamics Observatory (SDO) opened its eyes for the first time. Since then, the spacecraft has revolutionized our understanding of the star on our cosmic doorstep. Through the SDO's high definition view of the sun, solar mysteries have been solved and new mysteries have been revealed for the first time. Today, as the sun ramps up in activity -- fast approaching solar maximum, predicted to occur in 2013 -- our nearest star has generated the largest explosive event since 2006: an X-class solar flare. The "X7" flare reverberated through the inner solar system, causing a storm of high-energy protons to buzz around our planet, drenching our upper atmosphere in X-rays. Even though the flare was directed away from Earth, its impact was felt. To commemorate the most energetic flare in five years, Discovery News has teamed up with Camilla Corona SDO (the SDO's famous mission mascot) to collect some of the SDO's most breathtaking photographs of the past few months.
First Light On April 21, 2010, the first photographs from the SDO were received. One of the iconic first views of the high-definition sun was that of a rising prominence; an arc of solar plasma slowly rising into the sun's hot corona.
Valentines Flare Late on Feb. 14, 2011, while the world celebrated the final hours of Valentines Day, the sun let rip with Solar Cycle 24's first X-class solar flare. At the time, the X2 blast was the biggest since the previous cycle's X9 flare in Dec. 2006.
View Blocked The nature of the SDO's orbit around the Earth means it rarely has its view of the sun interrupted. But occasionally, an unavoidable celestial event causes a break in solar observing service. This partial solar eclipse, as witnessed on July 10, 2010, was the first eclipse experienced by the SDO. Note the edges of the moon's shadow across the sun's disk -- lunar mountains and valleys are silhouetted.
Prominence Rains Down On Feb. 24, 2011, the SDO zoomed in on an M-class flare (a "medium-sized" eruption) to see a vast amount of solar plasma rain back down toward the solar "surface" -- the photosphere.
Comet Death Comets often take a death-plunge deep into the solar corona, ultimately getting snuffed out of existence by the searing heat of the sun. Now we have an incredibly powerful solar observatory looking deep into the corona, we can see these "dirty snowballs" pay the ultimate price.
Coronal Rain What goes on deep in the sun's corona often stays deep in the sun's corona. Until now. With the help of the SDO, solar scientists are able to spot tiny dynamic features in the lowermost regions of the sun's atmosphere. One phenomenon characterized by the SDO is "coronal rain" -- blobs of hot solar plasma "raining" down onto the solar surface. Oh, and that black filament thing sitting in the center of the image? That's just a piece of fluff that stowed away with the SDO before it was launched, forever stuck in the telescope's lens.
Sunspots Sunspots are blemishes seen on the sun's surface. They are the side effect of the tangled magnetic fields from the solar interior getting forced through the sun's photosphere. As the hotter plasma above the photosphere is pushed away, the cooler interior is exposed, producing a dark spot. Sunspots are immensely detailed and the SDO can peer right into them, showing intricate plasma flows and magnetic structures. The pixelated textures surrounding this sunspot group is known as granulation -- regions where plasma up-wells from the solar interior and sinks again, like the convection of boiling water in a saucepan.
Twisting Prominence On March 19, 2011, a beautiful, twisting prominence erupted into space from the solar limb. The incredible detail of the hot solar plasma wrapped in a coiled magnetic field was easily captured as the arc expanded.
An Epic Event On June 7, 2011, something happened to the sun. This "something" baffled solar physicists. This "something" had never been seen before. During a "medium" M-class solar flare, a huge quantity of solar material was kicked into space, but most couldn't escape the sun's gravitational pull. The result was a dense, dark, "giant clod of dirt" that obscured the solar disk. A coronal mass ejection (CME) was also generated, but this fascinating eruption was notable for the strangeness of the imagery captured by the SDO.