An article published in “The Astrophysical Journal” reports a study on some structures that make up the solar plumes which are called plumelets in jargon. A team of researchers led by Vadim Uritsky of the Catholic University of America and NASA’s Goddard Space Flight Center applied cutting-edge image processing algorithms to NASA data to obtain unprecedented resolution images of solar plumelets. These structures are small but this study suggests they may play a crucial role in the solar wind, whose influence extends to the border with interstellar space.
The solar wind, with its energetic particles, transports the Sun’s magnetic field into space, influencing the planets and the other objects that are invested by it. The solar wind changes over time, and that’s why we speak of space weather. There are scientists who try to understand the processes that generate the solar wind and its changes because the Earth is protected by its own magnetic field but this doesn’t mean that it’s not affected by solar activity.
The solar magnetic field is complex, with closed loops and open lines along which the solar wind moves away from the Sun. On the solar surface, open magnetic field areas can create coronal holes, patches that appear dark at ultraviolets where the density is lower and there are geysers of materials that form plumes that are are bright at ultraviolets.
NASA’s Solar Dynamics Observatory (SDO) is a satellite launched on February 11, 2010, that, from a geostationary orbit, studies the Sun with a series of instruments. In particular, the ultraviolet images captured by the Atmospheric Imaging Assembly (AIA) instrument on July 2-3, 2016, were used in this study.
The solar plume studied has a brightness determined almost entirely by the individual plumelets. This suggests that they are more than just a feature of a larger system than a plume but the bricks that plumes are made of.
Judy Karpen of NASA’s Goddard Space Flight Center and one of the authors of this study explained that the structures inside and at the base of the plumes were already seen but she and her colleagues found that the plume is a bundle of plumelets. That’s quite different from the idea of plumes that researchers had so far.
Another discovery concerns the fact that plumelets move individually, oscillating independently. This suggests that the behavior of these small-scale structures could be a major source of disruption in the solar wind along with their collective large-scale behavior.
The Parker Solar Probe, which has already reached the shortest distance from the Sun reached by a spacecraft, will offer more crucial data. Already in its first Sun flyby in November 2018, it detected sudden reversals of the direction of the solar wind’s magnetic field, nicknamed switchbacks. Investigations into that phenomenon are still ongoing but structures such as plumelets could generate similar signatures.
Finding the signatures of plumelets in the solar wind also depends on how long they survive as they move away from the sun. Observatories like ESA and NASA’s Solar Orbiter will offer more information on these structures as well. NASA has also planned the PUNCH mission to directly observe the transitions from the atmosphere to the solar wind and could provide some answers helping to understand if the plumelets survive when they move away from the Sun.
This study shows that there are still important answers to be obtained regarding the processes taking place in the Sun and the solar wind. The powerful solar emissions make it difficult to observe their details and even more to observe them closely. The new missions started in recent years and planned for the near future will help to have some answers to better understand who the star that among other things allows life on Earth works.
