Sun's Oldest Mystery Solved: Why is Sun's Atmosphere Hotter Than Its Surface?

A question that has been boggling the scientists' mind for quite a while has finally been answered --- Why is the sun's outer atmosphere or corona millions of degrees hotter than its surface?

IFL Science reported that the solar corona is as hot as 1-3 million degrees, while the surface is a mere 6000°C.

"The problem of coronal heating was first discovered in the 1940s. The problem involves a variety of complex physical processes that are difficult to directly measure or capture in theoretical models," zolar physicist Bart De Pontieu of the Lockheed Martin Solar & Astrophysics Laboratory said in a press release.

In an attempt to solve the mystery, NASA has set up a space-based solar observatory called the Interface Region Imaging Spectrograph (IRIS).

"IRIS studies the transition region between the sun's surface and the corona," explains De Pontieu "It can track the temperature and motions of hot gas at unprecedented spatial (0.33 arcsec), temporal (2 s) and spectral (2 mi/s) resolution."

According to NASA's report, the IRIS's spectrographs showed evidence that "heat bombs" are partly heating up the sun's corona, and that the corona is heated in "discrete, bomb-like events."

Space.com notes that heat bombs occur when magnetic fields cross in the corona and realign, much like the process that causes solar flares.

The recent discovery not only answered where the heat of the corona is coming from, it also answered whether the corona is heated all at once or simultaneously.

According to Science Alert, in 2014, Jeff Brosius of NASA's Goddard Space Flight Center, together with his team came up with a separate study explaining the bizarre heating. The study, published in the Astrophysical Journal, supported the theory proposed by astrophysicist Thomas Gold in 1964, which states that burst of "nanoflares" is constantly heating up the corona, making it way hotter than its surface.

Aside from solving sun's oldest mystery, NASA notes that it could also help us in understanding solar storms better and could open up possible studies on nuclear fusion.