What heats the corona to such extreme temperatures?
X-ray jets seem to help. Cirtain and colleagues have examined four jets in great detail and found that they launch magnetic waves into the sun’s upper atmosphere. These waves, called Alfven waves, propagate into the corona where they *crack* like a whip, heating the gas where the crack occurs. (Note: When a whip is cracked on Earth, the sharp sound we hear is a result of energy being transferred from the fast-moving tip of the whip to the air around it. The same basic process is at work with Alfven waves cracking in the corona.) Cirtain doesn’t believe jets can wholly explain the super-heating of the corona, but “they make an important contribution.” Another team of Hinode researchers led by Bart De Pontieu of Lockheed-Martin have found evidence for more Alfven waves coming from a layer of the sun’s atmosphere called the chromosphere. (The chromosphere is to the sun as the troposphere is to Earth; both are near-surface layers of atmosphere.) These Alfven waves are not launched by jets
