The mystery relating to why sun's atmosphere is hotter than its surface is explained in a recent study.
The new observations came from just six minutes worth of data from one of NASA's least expensive type of missions, a sounding rocket, EUNIS (Extreme Ultraviolet Normal Incidence Spectrograph) mission, launched on April 23, 2013, which gathers a new snapshot of data every 1.3 seconds to track the properties of material over a wide range of temperatures in the complex solar atmosphere.
The new observations of the small-scale extremely hot temperatures are consistent with only one current theory: something called nanoflares - a constant peppering of impulsive bursts of heating, none of which could be individually detected provide the mysterious extra heat.
There are a variety of theories for what mechanisms power the impulsive bursts of heat, the nanoflares. Moreover, other explanations have been offered for what could be heating the corona. Scientists would continue to explore these ideas further, gathering additional observations as their tools and instruments improve. However, no other theory predicted material of this temperature in the corona, so this was a strong piece of evidence in favor of the nanoflare theory.
The study is published in the Astrophysical Journal.