New findings may help solve one of the biggest puzzles about the sun: Although its outer atmosphere, or corona, lies thousands of kilometers above the sun's visible surface, this distant region is about 1,000 times hotter than the surface. It's as if the air high above a candle were more blistering than the flame that heats it.
Scientists trying to explain this riddle haven't lacked for theories, but they've been stymied by a scarcity of data to test them. Observations from a NASA satellite called TRACE (Transition Region and Coronal Explorer) reveal for the first time that the energy for the heating is dumped in at the corona's base. The source of the heat remains uncertain.