Computer simulations show that the miniature solar flares nicknamed ‘campfires’, discovered last year by ESA’s Solar Orbiter, are likely driven by a process that may contribute significantly to the heating of the Sun’s outer atmosphere, or corona. If confirmed by further observations this adds a key piece to the puzzle of what heats the solar corona – one of the biggest mysteries in solar physics.
The Sun has a mysterious feature: somehow the tenuous outer atmosphere contains gas with a temperature of a million degrees, yet the solar surface is just 5500°C. Logic would suggest that if you have a body that is very hot at the center and relatively cool on the surface, it should be even cooler the further you go away. But the peculiar thing about the corona of the Sun – and many other stars as well – is that it starts to heat up the further you move above the surface. Many ideas have been put forward over the last decades homing in on the Sun’s magnetic field, but how the energy is generated, transported, and dissipated has been a source of much debate.
Enter Solar Orbiter, with one of its key goals to probe deeper into this mystery.
Stunning detail already provided by Solar Orbiter’s Extreme Ultraviolet Imager (EUI) ‘first light’ images just months after launch last year and since then has revealed more than 1500 small, flickering brightenings nicknamed campfires. These short-lived campfires last for between 10 and 200 seconds, and have a footprint covering between 400 and 4000 km. The smallest and weakest events, which had not been observed before, seem to be the most abundant, and represent a previously unseen fine structure of the region where the heating mystery is suspected to be rooted.
Yajie Chen, a PhD student from Peking University in China, working with Professor Hardi Peter from the Max Planck Institute for Solar System Research in Germany and colleagues, used a computer model to dive into the physics of the campfires, with exciting first results.
“Our model calculates the emission, or energy, from the Sun as you would expect a real instrument to measure,” explains Hardi. “The model generated brightenings just like the campfires. Furthermore, it traces out the magnetic field lines, allowing us to see the changes of the magnetic field in and around the brightening events over time, telling us that a process called component reconnection seems to be at work.”
Reconnection is a well-known phenomenon whereby…
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