Understanding the solar wind is fundamental to understanding our solar system and others in the universe. Made of electrons, protons and heavier ions, the solar wind flows through the solar system at about 1 million miles per hour.
However, what heats and speeds up the solar wind remains a mystery. A new study helps scientists solve this mystery and uncover important new clues about the origin of the solar wind. Scientists with NASA’s Parker Solar Probe mission have found that the solar wind can be largely fueled by small-scale jets or “jetlets” at the base of the corona.
Jetlets are known to be caused by a process known as magnetic reconnection, which occurs when magnetic field lines become entangled and explosively realigned. In the solar corona, the reconnection creates these ephemeral jets of plasma that pass energy and material into the upper corona, escaping through the solar system as the solar wind.
Nour Raouafi, the study leader and the Parker Solar Probe project scientist at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, said: “These new data show us how the solar wind kicks in at its source. You can see the stream of the solar wind rising from tiny million-degree jets of plasma over the base of the corona. These findings will have a huge impact on our understanding of the warming and acceleration of the coronal and solar wind plasma.”
The solar wind often blows continuously on the Earth. That’s why scientists have been looking for a consistent source from the sun that can sustainably power the solar wind. The latest research suggests that the solar wind may be generated and fueled primarily by individual jetlets erupting sporadically in the lower part of the corona. Even if each jetlet is only a few hundred miles long, the combined mass and energy could be enough to produce solar wind.
Craig DeForest, a solar physicist at the Southwest Research Institute in Boulder, Colorado, and co-author of the new paper, said: “This result implies that essentially all of the solar wind is released intermittently and becomes a steady stream, in much the same way that the individual clapping sounds in an auditorium become a steady roar when an audience applauds. This changes the paradigm for how we think about certain aspects of the solar wind.”
To the jetlets and magnetic fields. Switchbacks, magnetic zigzag formations in the solar wind, are a phenomenon initially spotted by Parker Solar Probe and served as inspiration for the entire study.
The scientists were able to understand the collective behavior of the jetlets thanks to the combination of observations from different vantage points, their high resolution, and the close-up observations from Parker Solar Probe.
Judy Karpen, a co-author of the paper and a heliophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said: “Previously, we couldn’t detect enough such events to explain the observed amount of mass and energy flows from the sun. But the improved resolution of the observations and meticulous data processing made the new findings possible.”
The findings showed the presence of jetlets in the lower solar atmosphere on the entire sun. Thus, unlike other phenomena that wax and wane with the 11-year cycle of solar activity, such as solar flares and coronal mass ejections, they are a sustainable driver of the continuous solar wind. The scientists also estimate that the energy and mass created by the jetlets could make up the majority, if not all, of the energy and mass observed in the solar wind.
Raouafi said, “The small reconnection events we observed are, in a way, what Eugene Parker envisioned more than three decades ago. I am convinced that we are on the right track to understanding the solar wind and corona heating.”
Continued observations from Parker Solar Probe and other instruments, such as NASA’s Polarimeter to Unite the Corona and Heliosphere, or PUNCH, and the Daniel K. Inouye Solar Telescope, will help scientists confirm whether jetlets are the main source of solar wind.
- Nour E. Raouafi, G. Stenborg, et al. Magnetic reconnection as the driver of the solar wind. The Astrophysical Journal. DOI: 10.48550/arXiv.2301.00903