August 18, 2009

Study: Nanoflares heat the sun’s corona

The mystery of why temperatures in the sun's outer atmosphere are higher than near the sun's surface may have been solved by Japan's Hinode satellite.

James Klimchuk, an astrophysicist at NASA's Goddard Space Flight Center's Solar Physics Laboratory, says new observations by that satellite have revealed why temperatures in the solar corona, the sun's outer atmosphere, soar to several million degrees Kelvin -- much higher than temperatures nearer the sun's surface.

The answer is nanoflares -- 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, Klimchuk said, noting coronal loops are the fundamental building blocks of the thin, translucent gas known as the sun's corona.

Scientists previously thought steady heating explained the corona's million degree temperatures. Klimchuk said the steady heating model indicates a coronal loop of a given length and temperature should have a specific density. However, new observations showed coronal loops have much higher density than the steady heating model predicts. Newer models based on nanoflares can explain the observed density, he said. But no direct evidence of the nanoflares existed until now.

The research was presented this month in Rio de Janeiro during a meeting of the International Astronomical Union's General Assembly.