Observing oscillations, flares and tornados on the sun

For six and a half days in July 2024, the balloon-borne solar observatory Sunrise III kept its gaze fixed on the sun. The stratospheric flight, which stretched from the northernmost tip of Sweden to Canada’s Northwest Territories, yielded a treasure trove of data exceeding 200 terabytes. These observations are unique. They provide insights—unprecedented in detail—into a layer of the sun approximately 2,000 kilometers thick and can continuously track its immense dynamics over several hours.

This region encompasses the sun’s visible surface, the so-called photosphere, as well as the adjacent chromosphere above it. The complex interplay of hot plasma, fluctuating magnetic fields and waves in this region is responsible, among other things, for our star’s violent outbursts that hurl particles and radiation into space.

Understanding solar eruptions

During the flight, the sun itself offered a comprehensive showcase of its capabilities: In addition to calm regions representing its moderate “normal” state, numerous signs of its temperament were also visible—such as sunspots, small and large solar flares, and regions of particularly high magnetic field strength.

A review article summarizing the mission’s first scientific results is published in The Astrophysical Journal Letters and marks the start of a comprehensive focus issue, which is dedicated exclusively to the results of the Sunrise III mission. Individual studies based on Sunrise III data will gradually be added to the focus issue.

“Sunrise III has already permanently changed our view of the sun. The data show how minute structures and rapid processes in the photosphere and chromosphere determine the impetuous nature of our star,” said Sami K. Solanki, director at the Max Planck Institute for Solar System Research and Sunrise III principal investigator.

“The results already available are as diverse as the sun itself,” says MPS researcher Smitha Narayanamurthy, co-author of the review article and head of the Science Working Group for Sunrise III. “They reveal new insights into the sun’s quiescent state and help us understand its volatile side,” she adds. Here are some of the new findings, which will be published in the next days and weeks:

Oscillations: Turbulent plasma flows inside the sun generate waves that propagate throughout the entire star, all the way to its lower atmosphere. Acoustic waves with periods of about five minutes have so far been observed mainly in a layer about 100 to 200 kilometers above the sun’s visible surface. Sunrise III provides a significantly more detailed view. For the first time, researchers were able to track the propagation of these waves within the photosphere and chromosphere—a layer with a total thickness of 2,000 kilometers—and study the influence of the magnetic field present there.

Solar flare: During the Sunrise III flight, a solar flare of the second-strongest category occurred on the sun. Such a flare can cause moderate disruptions on Earth, for example, in power grids or satellite systems. Sunrise III was able to track the flare in minute detail. In the chromosphere, elongated, brightly flashing structures appear during a solar flare. They form when magnetic field lines rearrange themselves there, thereby releasing energy. The Sunrise III data provide precise insights into the fine structure and changes in the magnetic field at these locations. This can help researchers understand how small-scale processes in the chromosphere regulate the evolution of large solar flares.

Solar tornados: The magnetic field lines extending from quiet regions of the sun’s surface into the chromosphere were previously considered to have a comparatively “orderly” structure. Sunrise III data, combined with computer simulations, now paint a different picture: Finely twisted magnetic field lines are embedded within ordered magnetic strands. They control the flows of hot plasma in the chromosphere and are thus likely to be the sites of small “solar tornados.”

So far, only a small portion of the Sunrise III data has been analyzed. “We’re still just at the very beginning,” says Sunrise III project manager Andreas Korpi-Lagg. “The data from the Sunrise III mission will keep us busy for many years to come—and will certainly hold a surprise or two,” he adds.

Stratosphere offers unobstructed view

Primarily responsible for the high quality of the Sunrise III data—and thus for the mission’s success—was the observatory’s “workplace.” In the stratosphere, about 35 kilometers (22 miles) above Earth’s surface, the observatory left most of Earth’s atmosphere behind. This layer of ever-moving air significantly limits the view of ground-based solar telescopes. Even with state-of-the-art techniques designed to compensate for atmospheric turbulence, only in extremely rare cases can the sun be observed for more than a few minutes at a time without interruption and with consistently high image quality.

Sunrise III, on the other hand, was able to conduct an observation series lasting several hours. Even the onset of night caused little disruption: Along Sunrise III’s summer flight path near the Arctic Circle, the sun sank very low for only a short time each day. Only during this period did the view through denser layers of Earth’s atmosphere impair Sunrise’s observations.

Equally crucial was the observatory’s scientific equipment: The telescope, with a primary mirror diameter of 1 meter (3.3 feet), captured the sunlight; the three instruments SUSI (ultraviolet spectropolarimeter), TuMag (magnetograph), and SCIP (infrared spectropolarimeter) processed it further; and a sophisticated image stabilization system ensured sharp images. Equipped in this way, the observatory captured image sequences at intervals of about a quarter of a second, revealing structures as small as 50 kilometers (31 miles) in size—all from a distance of nearly 150 million kilometers (93 million miles).

In addition, Sunrise III studied a broad wavelength range of the sunlight—from ultraviolet to infrared light—and could even distinguish between very closely adjacent wavelengths. Ultraviolet light from the sun is inaccessible to ground-based telescopes, as most of this radiation is absorbed by Earth’s ozone layer.

Who’s behind this story?

Lisa Lock

BA art history, MA material culture. Former museum editor, paramedic, and transplant coordinator. Editing for Science X since 2021.

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Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

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