Tiny Jets on the Sun Power the Colossal Solar Wind

The solar wind, which is produced by streams of charged particles that continually blast off the sun's atmosphere and radiate forth at millions of kilometers per hour, is so large that it constitutes the outer boundary of our solar system.

Despite this wind's extensive range, its genesis has long baffled scientists. The solar wind is now said to be propelled by a collection of irregular, small-scale jetlike eruptions in the sun's corona, or outer layer. "The idea is similar to how individual clapping sounds in an auditorium become a steady roar as an audience applauds," said Craig DeForest, a solar physicist at the Southwest Research Institute in Boulder, Colorado, and one of the study's co-authors.

tiny jetlets that normally endure for several minutes are found in the corona, but until recently, scientists had only found a tiny number of them, mostly near the foot of plumes that emerged from colder, less dense portions of the corona known as coronal holes.

They are pervasive, according to the recent study. "Once you know how to find them, you see that they are everywhere in basically every structure in the corona all the time," said co-author and Southwest Research Institute solar physicist Dan Seaton.

The scientists discovered that the jetlets, which are each between 1,000 and 3,000 kilometers broad, are still there even during the solar minimum, the sun's 11-year cycle's least active period. This finding is in line with the solar wind's pervasiveness. Lead author of the study and solar physicist Nour Raouafi of the Johns Hopkins University Applied Physics Laboratory stated, "You can randomly pick any day and the jetlets are there, just like the solar wind."

The team presents proof that the jetlets are triggered by a mechanism known as magnetic reconnection, which heats and accelerates a plasma of charged particles, in the study outlining the new results, published last month in the Astrophysical Journal. According to the researchers, the jetlets then generate waves that heat the corona, allowing the plasma to defy gravity and combine into the solar wind.

"The numbers come out looking promising and show it is really quite possible that jetlets could supply the mass lost by the sun to the solar wind," said Charles Kankelborg, a solar physicist at Montana State University who was not affiliated with the study.

The Motor

The work of Eugene Parker, a pioneering solar physicist who passed away last year, gave rise to the hypothesis that a variety of small-scale, irregular occurrences may act as a single driving force for the solar wind. He proposed in 1988 that a "swarm of nanoflares" fueled by brief spikes in magnetic reconnection may heat the corona sufficiently to generate wind.

Due to the limited precision of magnetic measurements, it has been difficult to uncover proof of this small-scale reconnection.

The GOES-R satellites, better known as weather satellites, the Goode Solar Telescope at the Big Bear Solar Observatory, and NASA's Solar Dynamics Observatory were among the sources of high-resolution photos used in the current study. They discovered that areas of the corona that had previously seemed to be free of magnetic flux were really occupied by intricate magnetic fields. Several jetlets were also connected to particular reconnection occurrences by the scientists. Higher reconnection and jetting rates may be revealed by even finer-scale magnetic field measurements, according to the researchers.

The research team went on to propose that the jetlets produce a particular type of wave, known as an Alfvén wave, which heats the corona. Alfvén waves has been considered as a rival mechanism that may account for the solar wind. However, there is a growing consensus that these processes can cooperate. According to Judith Karpen, a solar physicist at NASA's Goddard Space Flight Center, "the widespread presence of these reconnection-driven jetlets offers a natural explanation for both reconnection and Alfvén waves powering the solar wind."

Future research should disclose coronal processes in unprecedented detail, according to researchers. They place their faith in more recent telescopes, such the Daniel K. Inouye Solar Telescope at the National Solar Observatory and the Solar Orbiter, a joint NASA-ESA mission that will launch in 2020.

Raouafi predicted that the range of jetting might extend from reasonably big events to the tiniest sizes, Parker's nanoflares.

Additionally, according to Jie Zhang, a solar physicist from George Mason University, jetlets could be connected to the sun's large-scale phenomena like flares and coronal mass ejections. According to him, "small-scale eruptions may play a role in transforming magnetic configurations into more coherent large-scale structures that can store large amounts of energy before erupting."

The legacy of Parker and his colleagues has, for the time being, been confirmed by the recent jetlet discoveries. According to certain findings made 30 years later, they were most likely correct, said Kankelborg.