An article published in the magazine “Science” describes a research that provides an explanation of the origins of solar spicules, intermittent plasma jets that propagate from the solar chromosphere to the base of the corona at very high speeds. A team of researchers created computer simulations and compared them with observations made by NASA’s IRIS space probe and the Swedish Solar Telescope in the Canary Islands that confirmed the models’ validity.
Spicules were described for the first time in detail by Father Angelo Secchi in 1877. Over the years, researchers tried to understand their origin and role in energy transport in the solar atmosphere. There was the suspicion that this was an important source, if not the only one, of the heating of the solar corona, which can reach temperatures of millions of degrees, but so far no one had managed to solve the mystery of the spicules.
Now a team led by Juan Martinez-Sykora of the Bay Area Environmental Reasearch Institute at Petaluma and Lockheed Martin Solar and Astrophysics Laboratory offers an explanation after creating a computer model that simulated the formation and propagation of solar spicules. These simulations show the connection of the spicules with perturbations of the small-scale magnetic fields in the solar atmosphere.
According to these simulations, solar spicules form when the magnetic field lines’ tension is amplified and transported to the surface due to the interaction between charged and neutral particles. The tension is released suddenly ejecting energy and plasma that is heated up. Spicules are generated along with Alfvén waves, a powerful type of magnetic wave that scientists suspect to be a key in the solar atmosphere’s heating and solar wind thrust.
The presence of neutral particles is needed because charged particles only are not enough to bring the magnetic fields beyond the Sun’s surface. The interaction between charged and neutral particles allows the magnetic fields to move more freely up to the chromosphere where the tension is released into the spicules. Friction between ions and neutral particles heats plasma even more, both inside and around the spicules.
The presence of neutral particles was the element that made it difficult to create accurate simulations of spicules because their interactions require enormous computing power. NASA’s Pleiades supercomputer is very powerful and is at no. 15 of the world in the Top 500 ranking released a few days ago but its computing power must be split into many researches so the one about the spicules took a year to complete the simulations.
At that point, Juan Martinez-Sykora’s team had a model of solar spicules but its correctness needed to be verified. To do this, the researchers compared the simulations with observations carried out by NASA’s IRIS space probe, launched almost 4 years ago exactly to help discover the secrets of the Sun, and the Swedish Solar Telescope in the Canary Islands.
The image shows at the top solar spicules observed by the IRIS space probe’s spectrograph, in the central part a spicule simulation and in the lower part spicules observed by the Swedish Solar Telescope. It turned out that the simulations match the observations confirming the model’s validity.
This is a leap forward in understanding the processes underway in the solar atmosphere but the spicules are also involved in emitting the solar wind that hits the planets, including Earth. The consequence is that this type of research helps to understand physical phenomena ongoing in stars that are difficult to reproduce in the lab but also phenomena that directly affect us.
