Scientists previously thought steady heating explained the corona's million degree temperatures.

Observations from the NASA-funded X-Ray Telescope (XRT) and Extreme-ultraviolet Imaging Spectrometer (EIS) instruments aboard Hinode reveal that ultra-hot plasma is widespread in solar active regions.

The XRT measured plasma at 10 million degrees Kelvin, and the EIS measured plasma at five million degrees Kelvin; 273 degrees Kelvin equal zero degree Celsius.

'These temperatures can only be produced by impulsive energy bursts,' said Klimchuk, who presented the findings at the International Astronomical Union General Assembly meeting in Rio de Janeiro, Brazil.