What causes the Sun’s plasma jets?

Dynamic plasma jets called spicules (the thin lines of light pictured in the figure) flare up from the Sun at speeds of more than 200 km per second. At any given time, around 10 million of them are observable on the Sun’s surface. Some solar physicists have suggested that the plasma and energy that spicules carry upwards might help explain the high temperature of the Sun’s fiery corona (see the article by Jack Zirker and Oddbjørn Engvold, Physics Today, August 2017, page 36 ). Despite spicules’ abundance, however, previous models of the Sun have been unable to account for their frequency or for all of their observed properties, including the strong magnetic waves they carry.

Juan Martínez-Sykora and his colleagues at the Lockheed Martin Solar and Astrophysics Laboratory and the University of Oslo have developed a new model of the magnetic properties of the Sun’s plasma in an effort to understand spicule formation. They compared their simulation with data from NASA’s IRIS space telescope and from the ground-based Swedish 1-m Solar Telescope operated by Stockholm University. Their model shows that spicules form when magnetic tension on the Sun’s surface pushes plasma upward and that the release of that tension generates strong electrical currents and low-frequency plasma waves. Those currents and waves transmit significant amounts of energy. The findings suggest that spicules and their associated currents and waves could play a role in energizing the outer atmosphere of the Sun. (J. Martínez-Sykora et al., Science 356, 1269, 2017, doi:10.1126/science.aah5412 .)