In a paper published in the journal Nature Astronomy, the researchers report the world’s first clear images of nanojets in a process that reveals the existence of nanoflares – these are the potential candidates for heating the solar corona. Nanojets are bright, thin rays that move perpendicular to magnetic structures in the Sun’s atmosphere.
Scientists turned to NASA’s IRIS mission to find out why the Sun’s atmosphere is so much hotter than its surface and to understand what exactly is causing this heating. IRIS has been fine-tuned with a high-resolution thermal imager to zoom in on certain subtle events on the Sun.
Nanoflares are small explosions on the Sun but are difficult to detect. They are very fast and tiny, which means they are difficult to see on the bright surface of the Sun. On April 3, 2014, during a coronal rain, during which streams of cooled plasma fall from the corona onto the surface of the Sun and look like a huge waterfall, the researchers noticed bright jets appearing towards the end of the observed event. These pilot flares are nanojets — heated plasma moving at such a speed that they appear in images as bright, thin lines visible inside magnetic loops on the Sun.
It is believed that each nanojet is initiated by a process known as magnetic reconnection when the twisted magnetic fields change in an explosive manner. One reconnection can cause another, creating an avalanche of nanojets in the sun’s corona. It is this process that can create energy that heats the corona.
The researchers combined a variety of observations with advanced simulations to recreate the events they saw on the Sun. The models showed that nanojets were a characteristic feature of magnetic reconnection and nanoflares, contributing to the heating of the corona. More research needs to be done to establish the frequency of nanojets and nanoflares throughout the sun, as well as how much energy they contribute to heating the solar corona. Going forward, missions such as Solar Orbiter and Parker Solar Probe can provide more detailed information about the processes that heat the solar corona.