Because of its high temperatures, all matter in the Sun takes the form of gas and plasma. The gases below the solar surface bubble like a boiling soup, dragging magnetic field around. Any field in the solar atmosphere is anchored in these random motions, so that the atmospheric field loops become twisted and entwined into 'braids.' As the braids become more tightly wound like a twisted rubber band, they store enormous amounts of heat. Eventually, as the braids become severely distorted by the twisting, they snap and unwind, dissipating their heat into the solar corona. Large energy releases are known as solar flares. A multitude of smaller such events was speculated to occur to sustain the background coronal glow.
The Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory provided complimentary full-Sun images before during and after the Hi-C observations. The AIA images provided the essential context in analyzing the Hi-C data. In fact, it was AIA that captured a C-class solar flare centered on the braided magnetic field loops that Hi-C had imaged, about three minutes after the Hi-C flight had concluded. This provided conclusive proof of the energy release into the corona.
"The Hi-C observations zoom in on what happens within the global view of the Sun that is seen with NASA's Solar Dynamics Observatory. The combination of the big-picture view with the unprecedented Hi-C images shows us processes in action that we could only theorize about until now, processes that are fundamental to the workings of the solar atmosphere and all of space weather, and that apply at any other Sun-like star where we would never be able to see them in action," said Dr. Karel Schrijver of the Solar & Astrophysics Laboratory at the ATC. "The Hi-C images demonstrate that we now have the technology to make the next leap in understanding the Sun's violent magnetism."
"It is clear from the Hi-C observations that the closer we look at the Sun, the better we understand how it works," said co-author of the Nature paper Dr. Bart De Pontieu of the ATC, and lead scientist on NASA's upcoming Interface Region Imaging Spectrograph (IRIS) mission, scheduled for launch in April of this year. "IRIS will, in fact be looking at deeper layers of the Sun's atmosphere than Hi-C, and with similar resolution and time cadence. With IRIS, we'll be able to observe the same phenomena captured by Hi-C, but closer to where they emerge from the solar interior. As an example, it's analogous to our looking at the ocean and seeing how water evaporates and rains down. These we would see with an instrument like IRIS, whereas Hi-C would be viewing the clouds above. Moreover, IRIS will be in space continually, observing the Sun 24 hours a day, and thus enabling us to see many more events from start to finish."The Hi-C mission was led by Principal Investigator Dr. Jonathan Cirtain of the NASA Marshall Space Flight Center, who is also the lead author of the Nature paper published today. Co-authors are from the Harvard-Smithsonian Center for Astrophysics, the Lockheed Martin Solar and Astrophysics Laboratory at the ATC, the University of Alabama, the University of Central Lancashire, the Lebedev Physical Institute in Moscow, and the Southwest Research Institute in Boulder, Colo. The ATC is the research and development organization of Lockheed Martin Space Systems Company (LMSSC) and creates the technology foundation for the company's business. In addition, the ATC conducts research into understanding and predicting space weather and the behavior of our Sun, including its impacts on Earth and climate. It has a five-decade-long heritage of spaceborne instruments.