The Sun's corona—essentially its plasma "atmosphere"—is actually hotter than the surface of the star itself. Scientists have long suspected that the region's million-degree temperatures influence its massive magnetic fields, and have hypothesized that solar flares originate there. But researchers had never been able to observe these phenomena first-hand—until now.
The High Resolution Coronal Imager (Hi-C) is a 6-foot long, 464-pound suborbital telescope designed at the Marshall Space Flight Center in Huntsville, Alabama in conjunction with the Smithsonian Astrophysical Observatory and L-3Com Labs.
The mission's principal investigator, Dr. Jonathan Cirtain, describes its 9.5-inch primary mirror as "the finest pieces of glass ever fabricated for solar astrophysics." The mirror is roughly the same size as NASA's orbiting Sun-studying platform, the Solar Dynamics Observatory, but thanks to its 4k x 4k CCD Apogee imaging system, the Hi-C is able to stare deeper into the corona's extreme ultraviolet wavelengths, with five times the resolution as the SDO.
"We had never attempted such a program before and had to develop new techniques for grinding the optics and polishing the surfaces, not to mention figuring out how to mount them without diminishing the performance," Cirtain explained in a press release. "The final mirror surface is so smooth that it only deviates from being perfectly smooth by a few angstroms over the 24 cm optic."
On July 11, 2012, the $5 million Hi-C lifted off from White Sands Missile Range, New Mexico aboard a sounding rocket. Its suborbital flight lasted just 620 seconds from launch to parachute landing, but during that time the telescope captured 165 images (one every five seconds) that are already confirming hypotheses and changing what we thought we knew about solar weather.
By combining the data collected by Hi-C and supplementing it with data collected by the SDO, researchers are gleaming a new understanding of solar coronal dynamics. The Hi-C images show, for the first time, active energy transfers from the Sun's magnetic field to its corona, a process known that Solar Braiding, which has long been hypothesized and only now confirmed.
"Scientists have tried for decades to understand how the sun's dynamic atmosphere is heated to millions of degrees," said Cirtain. "Because of the level of solar activity, we were able to clearly focus on an active sunspot, and obtain some remarkable images. Seeing this for the first time is a major advance in understanding how our sun continuously generates the vast amount of energy needed to heat its atmosphere." [NASA 1, 2, Ars, Wikipedia, CCD]