Scientists have discovered a surprisingly complex network of magnetic structures above regions of the Sun that appear relatively calm. In 2024, an international team led by the National Astronomical Observatory of Japan (NAOJ) used the Sunrise III solar observatory, carried aboard a balloon into Earth’s stratosphere, to detect thin, filament-like magnetic signatures that had previously been difficult to observe. The findings offer new clues about how energy moves through the solar atmosphere and contributes to its heating.
A web of magnetic threads above the Sun
Sunrise III detected numerous thin, elongated magnetic structures above quiet regions of the Sun. These features are woven into a larger network of magnetic fields known as the magnetic canopy, which extends through the chromosphere, the layer of the solar atmosphere above the visible surface.
The canopy forms as magnetic fields concentrated at the Sun’s surface, or photosphere, spread outward and arch upward toward the chromosphere. The new observations show that it is not a smooth, uniformly expanding structure. Instead, it contains many narrow, thread-like features.
To investigate how these structures form, the researchers used computer simulations that reproduced the patterns recorded by Sunrise III. The results suggest that motion at the Sun’s surface twists the magnetic field lines, creating the complex structures observed higher in the atmosphere.
The observatory also examined another quiet region near the solar limb, the visible edge of the Sun. There, researchers measured magnetic fields in spicules: thin jets of solar material that extend upward from the surface. These measurements show how the distribution of the magnetic field changes with increasing height above the Sun’s visible edge.
Why quiet solar regions are difficult to study
Although the Sun is constantly active, much of its surface lacks obvious features such as sunspots. Scientists describe these relatively inactive areas as “quiet regions.” They cover a large portion of the Sun and are important for understanding how the star behaves.
However, quiet does not mean magnetically inactive. These regions contain magnetic fields that are generally weaker than those in more active areas. Their delicate structures are difficult to measure, particularly with ground-based telescopes, because turbulence in Earth’s atmosphere can blur fine details.
Sunrise III was designed to overcome this problem by carrying a powerful solar telescope high above the atmosphere.
A balloon-borne telescope reveals new details
Sunrise III is an international research project built around a one-meter telescope carried by a high-altitude balloon. During its 2024 mission, the observatory reached an altitude of about 35 kilometers, or roughly 22 miles, in the stratosphere, where atmospheric interference is greatly reduced.
This elevated vantage point enabled the telescope to make highly detailed measurements of the Sun’s magnetic field.
The balloon gondola carried three scientific instruments developed with donations from various countries. One of them was SCIP, the Sunrise Chromospheric Infrared spectroPolarimeter, a near-infrared instrument developed under the initiative of the National Astronomical Observatory of Japan.
SCIP is designed to measure magnetic fields continuously across different layers of the solar atmosphere, from the photosphere to the chromosphere. This allowed researchers to examine how magnetic structures spread and change with altitude rather than studying only a single layer.
Clues to how the solar atmosphere is heated
By observing from the stratosphere, Sunrise III produced an unusually detailed view of the magnetic field above a quiet solar region. The measurements showed that the chromosphere contains a far more complex magnetic structure than a simple expanding canopy.
Understanding these structures may help scientists determine how energy generated by motion near the Sun’s surface is transferred to the upper layers of the atmosphere.
The discovery is an important step toward explaining how magnetic activity contributes to heating the solar atmosphere, including regions that appear calm when viewed from a distance.
Source: www.sciencedaily.com