Nasa has posted video showing in unprecedented detail the hottest part of the Sun – its corona.
The footage, recorded in the extreme ultraviolet wavelength, was taken by a small piece of equipment that was flown on a suborbital rocket for just 10 minutes in July before making a parachute landing.
The 210-kilogram, 1.83-metre high resolution coronal imager telescope, known as Hi-C, took 165 images during the flight, focused on a large active region of the Sun.
The corona is the Sun's outermost layer. It is thin and faint and therefore difficult to see from the Earth.
The Smithsonian Astrophysical Observatory, a partner in the project, said astronomers had been puzzled for decades by the fact the corona could heat to temperatures of 3.9 million degrees Celsius, while the Sun's visible surface was 5500C.
Hi-C had provided a major piece of the puzzle, the observatory said.
The telescope revealed a mechanism that pumped energy into the corona, heating it. The secret was a complex process known as magnetic reconnection.
"This is the first time we've had images at high enough resolution to directly observe magnetic reconnection," Smithsonian astronomer Leon Golub said.
"We can see details in the corona five times finer than any other instrument."
Heliophysicist Jonathan Cirtain from the Marshall Space Flight Center said the team had developed an exceptional instrument capable of revolutionary image resolution of the solar atmosphere.
"Due to the level of activity, we were able to clearly focus on an active sunspot, thereby obtaining some remarkable images," Cirtain said.
The Sun's activity, including solar flares and plasma eruptions, was powered by magnetic fields, the observatory said.
Its surface was like a collection of 1600-kilometre-long magnets scattered around after bubbling up from inside the Sun.
Magnetic fields poked out of one spot and looped around to another spot. Plasma flowed along those fields, outlining them with glowing threads.
The images from Hi-C showed interweaved magnetic fields that were braided like hair. When those braids relaxed and straightened, they released energy.
The observatory said Hi-C witnessed such an event during its flight.
The telescope also detected an area where magnetic field lines crossed in an X, then straightened out as the fields reconnected. Minutes later, that spot erupted with a mini solar flare.
"Hi-C showed that the Sun is dynamic, with magnetic fields constantly warping, twisting, and colliding in bursts of energy," it said.
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