Washington, Aug 17 - The mystery of why temperatures in the sun's outer atmosphere soar to several million degrees, far hotter than temperatures near the sun's surface, has been solved.

New observations made with instruments aboard Japan's Hinode satellite reveal the hotter outer atmosphere is due to nanoflares.

Nanoflares are small, sudden bursts of heat and energy. 'They occur within tiny strands that are bundled together to form a magnetic tube called a coronal loop,' said James Klimchuk, an astrophysicist at the Goddard Space Flight Centre's Solar Physics Lab in Maryland.

Coronal loops are the fundamental building blocks of the thin, translucent gas known as the sun's corona.