New technology is now allowing astronomers to begin forming hypotheses about why the sun’s outer atmosphere, called the corona, is much hotter than its surface.
NASA’s High-resolution Imager, or Hi-C, seems to have an answer. According to the U.S. space agency, energy is actively pumped to the outer parts of the sun’s atmosphere, making it hotter than areas closer to the sun, raising the atmosphere’s temperature to millions of degrees.
The part of the sun that we can see is called the photosphere and burns at around 10,000 degrees Fahrenheit. Farther from the center of sun is the corona, an area of increased heat made of ionized gas and plasma. The corona is usually only visible during a solar eclipse when it glows white around the hidden sun.
The intense heat of the corona has puzzled scientists for years. Traditionally, the farther from the center of a hot object, the colder it gets. However, with the corona, the opposite is true. The atmosphere farther from the sun in the corona is actually hotter than that closer to the solar center at roughly 7 million degrees F.
The Hi-C, which was launched along with a suborbital rocket mission in July of 2012, has revealed a major clue to the how the corona of the sun works. According to the imager’s findings, the corona burns extra hot because of phenomena known as magnetic reconnection.
In a study published in the journal Nature, a team of astronomers describe magnetic “braids” in the sun’s corona. The sun’s magnetic braids, which loop around the entire surface of the massive star, seem to relax and straighten as they release energy. These bursts of energy are what heat the corona to nearly 7 million degrees F, astronomers say, and it could explain the massive difference in temperature.
According to Leon Golub, of the Harvard-Smithsonian Center for Astrophysics, Hi-C has allowed the research team to learn more about the corona than was previously known.
“This is the first time we’ve had images at high enough resolution to directly observe magnetic reconnection,” he said. “We can see details in the corona five times finer than any other instrument.”
Jonathan Cirtain, a heliophysicist at the Marshall Space Flight Center, is excited about the images Hi-C was able to obtain, saying it provides astronomers with unprecedented data that will likely lead to a better understanding of how stars — and the sun in particular — evolve to produce energy.
“Our team 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,” he said.
The scientists involved study are thrilled with what Hi-C uncovered about the sun’s greatest conundrum. Next, they plan to work on building a satellite that could observe the sun’s magnetic fields constantly with as much precision as Hi-C. “We learned so much in just five minutes. Imagine what we could learn by watching the Sun 24/7 with this telescope,” Golub said.
While the findings may seem trivial, the team did not that it has one significant possible practical application: better space weather forecasts. With the sun’s solar storm cycle expected to peak this year, it could better prepare Earth for the massive barrage of solar particles unleashed by our nearest star.