The Sun’s corona, or outer atmosphere, is about 300 times hotter than its surface. This phenomenon has puzzled scientists for the past several decades. They wondered why the surface, which should be hotter, is cooler than the corona. Finally, scientists at NASA have gathered evidence that explains this phenomenon. After analyzing a six-minute footage from the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) mission, scientists said that it has something to do with nanoflares.

Sun Corona

Nanoflares can’t be detected individually

Nanoflares are the consistent showering of impulsive heat bursts. Surprisingly, though they provide extra heat in rapid bursts, nanoflares can’t be detected individually. A team of scientists led by Jeff Brosius of NASA’s Goddard Space Flight Center published the study in The Astrophysical Journal. The U.S. space agency launched EUNIS on April 23, 2013 to track the sun’s complex properties.

An instrument like EUNIS works properly only in space. The spectrograph records various light wavelengths to collect data on the amount of material found in a given temperature. Just six minutes of data gathering from EUNIS suggests that the temperature of the sun’s photosphere is about 6,000 degrees Kelvin, but its corona is 300 times hotter. Photosphere is the sun’s surface that we see from the Earth.

NASA says EUNIS will continue to make further observations

The spectrograph selected an “active region” and then calculated 10 million degrees Kelvin coming out of many different wavelengths. Scientists analyzed these unique emission lines to theorize that nanoflares can definitely produce a temperature reading of 10 million degrees Kelvin. Brosius is glad to see the spectrograph’s ability to resolve the weak emission lines so clearly. He said it’s the strongest evidence for the presence of nanoflares.

Nanoflares cool down pretty quickly, resulting into a lot of solar material at 1-2 million degrees Kelvin, which is often seen in the corona. NASA said EUNIS has led to an important discovery related to the sun. It will continue to examine the issue and make further observations. NASA scientist Adrian Daw said that this mission has proved that the smaller, inexpensive sounding rockets are capable of producing robust science.