ESA/NASA Solar Orbiter Mission Unveils Elusive Source of Solar Wind

The ESA/NASA Solar Orbiter spacecraft has recently made a groundbreaking discovery that could revolutionize our understanding of the sun's outer atmosphere and the mechanisms behind the solar wind. In a publication in the journal Science, researchers have revealed that Solar Orbiter has detected a plethora of minuscule jets of material erupting from the sun's outer atmosphere. These jets, lasting between 20 and 100 seconds each, expel plasma at astonishing speeds of around 100 km/s. Importantly, these findings suggest that these tiny jets might be the long-sought source of the solar wind.

This mosaic of images shows a multitude of tiny jets of material escaping from the sun’s outer atmosphere. The images come from the ESA/NASA Solar Orbiter spacecraft. They show up as dark streaks across the solar surface in this mosaic. The images are ‘negatives’ meaning that although the jets are displayed as dark, they are bright flashes against the solar surface. Each jet lasts between 20 and 100 seconds, and expels charged particles, known as plasma, at around 100 km/s. These events could be the long-sought-after source of the ‘solar wind’, the constant outflow of charged particles that comes from the sun and flows through the solar system. In this collage of images, the sun’s south pole is to the left. Credit: ESA & NASA/Solar Orbiter/EUI Team; acknowledgement: Lakshmi Pradeep Chitta, Max Planck Institute for solar system Research, CC BY-SA 3.0 IGO

The solar wind, composed of charged particles or plasma, is a continuous stream of solar material that radiates outward from the sun and permeates interplanetary space. When these particles interact with Earth's magnetic field, they produce the mesmerizing phenomena known as auroras. Despite its fundamental role in our solar system, understanding the origin and generation of the solar wind has eluded scientists for decades.

The Solar Orbiter's Extreme Ultraviolet Imager (EUI) instrument has been pivotal in shedding light on this enigma. On March 30, 2022, the EUI captured images of the sun's south pole that revealed transient features linked to small jets of plasma escaping the sun's atmosphere.

Lead author Lakshmi Pradeep Chitta from the Max Planck Institute for Solar System Research in Germany emphasized the significance of this discovery: "These tiny jets were detectable due to the unprecedented high-resolution and high-cadence images provided by the EUI. The extreme ultraviolet channel of EUI's high-resolution imager, which observes million-degree solar plasma at a wavelength of 17.4 nanometers, played a crucial role."

What makes these findings even more intriguing is that they confirm that these features are indeed linked to plasma ejections from the solar atmosphere. While scientists have long understood that magnetic structures called coronal holes are associated with a significant portion of the solar wind, the exact processes leading to plasma expulsion remained uncertain. These coronal holes are regions where the sun's magnetic field extends deep into space instead of looping back into the sun.

Traditionally, it was assumed that the sun's hot corona would naturally expand, leading to the escape of plasma along these open magnetic field lines. However, the Solar Orbiter's observations of individual jets challenge this assumption. The jets were particularly prominent in a coronal hole situated at the sun's south pole. This implies that the solar wind might not solely result from a steady continuous flow but could involve highly intermittent outflows.

Andrei Zhukov from the Royal Observatory of Belgium, a collaborator on the project, noted, "The ubiquity of the jets suggests that the solar wind from coronal holes might originate as a highly intermittent outflow."

Despite their small energy associated with each individual jet, these findings suggest that they collectively contribute a substantial fraction of the material observed in the solar wind. Researchers anticipate that even smaller and more frequent events could contribute further to this phenomenon.

David Berghmans, the principal investigator for the EUI instrument at the Royal Observatory of Belgium, expressed the significance of this discovery: "I think it's a significant step to find something on the disk that certainly is contributing to the solar wind."

As the Solar Orbiter continues its mission, gradually inclining its orbit towards the polar regions, researchers anticipate gaining a fresh perspective on these tiny jets. This is crucial for studying their properties and behavior from different angles, enhancing our understanding of their role in powering the solar wind.

Beyond its implications for our solar system, this research extends its significance to other stars. While the sun remains the only star whose atmosphere we can study in such depth, the processes unveiled by Solar Orbiter could potentially apply to other stars, transforming these findings into a fundamental astrophysical breakthrough.

Journal Information: L. P. Chitta et al, Picoflare jets power the solar wind emerging from a coronal hole on the Sun, Science (2023). DOI: 10.1126/science.ade5801