Scientists now understand why the sun's outer atmosphere or corona is far hotter than its surface.

Data from the Extreme Ultraviolet Normal Incidence Spectrograph (EUNIS) spacecraft launched on April 23, 2013 confirm that the small but extremely hot temperatures hammering the sun are consistent with only one current theory: nanoflares.

Like Us on Facebook

Incapable of being detected until now, nanoflares provide the mysterious extra heat that ignites the sun's outer atmosphere.

Using a very sensitive spectrograph, EUNIS recorded data from the corona every 1.3 seconds over a range of temperatures in the solar atmosphere.

A spectrograph is a device that gathers information on the number of materials present at a given temperature by recording different light wavelengths.

Jeff Brosius, a scientist from the Catholic University at Washington D.C., said data from EUNIS is a puzzle because things usually become cooler farther away from a heat source.

He explained that the photosphere, sun's visible surface, has a temperature of 6,000 Kelvin while the sun's corona reaches a temperature 300 times hotter.

Launched to a height of 200 miles above the Earth aboard a sounding rocket, EUNIS gathered six minutes worth of observation from above the Earth's atmosphere.

It scanned an active region of the sun which is the source of large solar flares and coronal mass ejections.

Adrian Daw, EUNIS principal investigator, said using EUNIS for this study was a less expensive way of producing a robust science find.

The EUNIS mission offers a valuable test bed for new technology that may subsequently be flown on long-term space mission.

EUNIS will fly again in 2016 where it will focus on different solar wavelengths that can spot the extremely high temperature materials like nanoflares.