The surface of the Sun is a very cold place. When compare it with the crown, the upper atmosphere of the Sun, which is almost 400 times hotter. This large temperature difference has long been a mystery, but a newly discovered feature in the Sun's magnetic field could help us get to the bottom of it.
The Sun's magnetic field tangled includes huge loops forming an arc from the surface to the crown. We can see the bright loops because the surface plasma flows along its curves.
Richard Frazin of the University of Michigan, Ann Arbor, and his team measured the temperature of coronal loops during solar minimum, a period in which they are quiet fewer sunspots and flares. They hoped that all loops were warmed with height, since that was the case in the measurements made during the most active phases.
Surprisingly, some of the loops near the Sun Ecuador cooled closer to their tops. Frazin believes these "small loops" recently discovered there throughout the solar cycle and can be an indication of what it is that causes coronal heating. Clare Parnell of the University of St. Andrews, UK, agrees that small loops are a new factor that any model must include solar heating.