Scientists discovered the important clue while observing immense coils of hot, electrified gas, known as coronal loops, which have been seen in unprecedented detail by Trace.
Astronomers also hope to use the solar corona studies to better understand other stars.
A forthcoming paper in the Astrophysical Journal, Locating the Source of Coronal Heating, is seen as an important advance in understanding the puzzle. The gas fountains seen in the Trace images form arches hundreds of thousands of kilometres in height and are capable of surrounding 30 Earths. The conventional theory assumes that the loops are heated evenly. However, Trace observations show that most of the heating must occur at the base of the loops, near where they emerge from and return to the solar surface. If this were not so, the lower parts would have been much cooler than the tops, which do not lose heat as quickly.