The outermost part of the atmosphere of the Sun, the solar corona, is almost 1,000 times hotter than the Sun’s surface. Scientists are yet to find the crucial mechanism or mechanisms behind this peculiar disparity but we might be getting closer to solving this mystery.
Last year, the European Space Agency’s Solar Orbiter delivered the closest image of the Sun yet. Those first images delivered some exciting and unexpected discoveries a whole year before the official scientific mission begins. Solar Orbiter’s Extreme Ultraviolet Imager (EUI) observed 1,500 small flickering solar flares, revealed to be a new phenomenon dubbed "campfires," near the surface of the Sun.
Now, new work presented at the European Geosciences Union (EGU) General Assembly suggests that if our understanding of these miniature flares is correct, they could be crucial to heating up the Sun's corona. The Sun's surface is 5,500°C (10,000°F), but its corona is around 1 million °C (1.8 million °F). It's not known why it gets hotter the further from the surface of the star you get, but the Sun's magnetic field is a likely contender. How that energy is generated and transported, however, is up for debate.
“Our model shows that the energy released from the brightenings through component reconnection could be enough to maintain the temperature of the solar corona predicted from observations,” Yajie Chen, from Peking University, whose research is accepted in Astronomy and Astrophysics, said in a statement.
While the model is exciting, it is still very early days. Solar Orbiter’s full science mission doesn't actually start until November this year, where more observations will be taken. Then the model can be further tested and refined and hopefully, it will hold. If confirmed, this could be a key piece of the puzzle of the Sun's temperature disparity.
A second paper, also published in Astronomy and Astrophysics, provides more insight into what we currently know of the campfires. They tend to last between 10 and 200 seconds, extending between 400 and 4,000 kilometers (250 to 2,500 miles). Researchers employed observations from NASA’s Solar Dynamics Observatory to actually work out where in the solar atmosphere these campfires happen.
“To our surprise, campfires are located very low in the solar atmosphere, only a few thousand kilometers above the solar surface, the photosphere,” lead author David Berghmans, principal investigator of EUI, said. “It is very early days, and we are still learning a lot about the campfire characteristics. For example, even though campfires look like small coronal loops, their length is on average a bit short for their height, suggesting we only see part of these little loops. But our preliminary analysis also shows that campfires do not really change their height during their lifetime, setting them aside from jet-like features.”
Understanding these campfires, what drives them, and their relationship with other solar phenomena will help scientists delve deeper into the curious solar corona puzzle.
Solar Orbiter is already showing us the Sun as we have never seen before but the best is yet to come. Among the many exciting things this mission will deliver are observations of the Sun's polar regions, something we have never seen before.