In an article published today in Nature Astronomy, researchers report the first clear images of nanojets – bright, thin lights moving perpendicular to the magnetic structures in the solar atmosphere called the corona – in a process that suggests the existence of one of revealed to them the potential candidate for coronal heating: Nanoflares.
To understand why the solar atmosphere is so much hotter than the surface, and to distinguish between a variety of theories about what causes this warming, researchers on NASA’s IRIS (Interface Region Imaging Spectrograph) mission turn to NASA. IRIS has been fine-tuned with a high resolution imager to magnify certain hard-to-see events on the sun.
Nanoflares are small explosions on the sun – but they are difficult to see. They’re very fast and tiny, which means they’re difficult to see against the sun’s bright surface. On April 3, 2014, researchers noticed bright jets near the end of the event during a so-called coronal rain event, where streams of cooled plasma from the corona fall onto the sun’s surface and look almost like a giant waterfall. These tell-tale flashes are nanojets – heated plasma that spreads so quickly that they appear in images as bright, thin lines that can be seen in the sun’s magnetic loops. Nanojets are considered a “smoking weapon”, important evidence of the presence of nanoflares. It is believed that every nanojet is triggered by a process known as magnetic reconnection, in which twisted magnetic fields explosively realign themselves. One reconnection can trigger another reconnection and create an avalanche of nanojets in the sun’s corona, a process that could create the energy that heats the corona. In the visualization above, the Solar Dynamic Observatory gives us a full view of the sun before zooming into IRIS ‘close-up view of the nanojets briefly flashing in the magnetic loops.
IRIS collects its high-resolution images by focusing on a small part of the sun at a time. So observing certain events is a combination of well-grounded guesswork and the right place at the right time. After identifying the nanojets against the backdrop of coronal rain, the researchers coordinated with NASA’s Solar Dynamics Observatory (SDO) and the Hinode Observatory, a partnership between the Japan Aerospace Exploration Agency, ESA (European Space Agency) and NASA for a full analysis, look at the sun and confirm if they spotted nanojets and evaluate their impact on the corona.
The researchers combined the many observations with advanced simulations to recreate the events they saw on the sun. The models showed that the nanojets were a tell-tale signature for magnetic reconnection and nanoflares that contributed to coronal heating in the simulations. More studies need to be done to determine the frequency of nanojets and nanoflares throughout the sun and how much energy they are adding to the warming of the solar corona. In the future, missions like Solar Orbiter and Parker Solar Probe can provide more detailed information about the processes that heat the solar corona.
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