Tiny Loops, Big Clues: How Hidden Solar Structures Are Shedding Light On The Sun's Explosive Energy
Scientists observed tiny, short-lived plasma loops in the Sun’s lower atmosphere, offering new insights into magnetic energy release and coronal heating mechanisms.
By Anubha Jain
Published : July 19, 2025 at 5:43 PM IST
Bengaluru: Astronomers from the Indian Institute of Astrophysics (IIA), alongside global collaborators, have uncovered miniature plasma loops in the Sun’s lower atmosphere. These short-lived, thread-like arcs—just 3,000–4,000 km long (roughly the distance from Kashmir to Kanyakumari) and under 100 km wide—had remained hidden so far due to their tiny size and fleeting lifespan.
Among the most intriguing features of the Sun’s outer layer are coronal loops, arc-like, beautiful structures of hot plasma that glow at a temperature over a million degrees. However, they hold clues to the Sun's deepest mysteries and unleash magnetic energy.
The study, published in The Astrophysical Journal, was carried out by an international team led by Annu Bura, Tanmoy Samanta, Jayant Joshi from IIA, and global collaborators from NASA, the Max Planck Institute for Solar System Research (MPS) in Germany and the Big Bear Solar Observatory (BBSO) in the USA.
Global Collaboration and Tools Used
Using powerful telescopes like NASA's Interface Region Imaging Spectrograph (IRIS), the Solar Dynamics Observatory (SDO), and the Goode Solar Telescope at BBSO, scientists from top global institutes worked together to spot these tiny loops. By observing them in visible, UV, and extreme-UV light, they could track how the loops behave across different layers of the Sun’s atmosphere.
“These tiny loops live fast and die young, lasting only a few minutes, making it extremely difficult to observe them and interpret their physical origins. They offer a new window into how magnetic energy is released in the solar atmosphere on small scales,” said Annu Bura, a PhD student at IIA and the first author of the paper. Annu calls these structures "small but mighty," as they display magnetic reconnection events—violent realignments of magnetic field lines that power solar flares and eruptions.
Talking to ETV Bharat, IIA's Assistant Professors and co-authors of the study, Tanmoy Samanta and Jayant Joshi, described the entire research work.
Emphasising the discovery of miniature plasma loops in the Sun’s lower atmosphere, Tanmoy Samanta said, “With advancements in observational technology and by combining data from multiple instruments, we have, for the first time, directly observed very small-scale magnetic loops in the Sun. These loops, which were previously unresolved and undetected, appear in specific wavelengths and temperature regimes within the solar atmosphere.”
He explained that the team utilised three different instruments, including those sensitive to ultraviolet (UV) and extreme ultraviolet (EUV) radiation. “We incorporated data from a ground-based solar telescope in the United States—one of the largest of its kind—alongside observations from space-based instruments. This multi-instrument approach enabled us to resolve fine-scale plasma structures that appear to form the fundamental building blocks of the solar corona.”
Observational Techniques and Wavelength Analysis
Discussing the role of high-resolution Hydrogen-alpha (Hα) imaging, Samanta elaborated, “The Hα line helps study the Sun’s chromosphere and cooler parts of its atmosphere. In this study, scientists used narrowband filters to look at specific parts of the Hα line and found tiny plasma loops visible only in certain narrow regions.” He clarified that while Hα imaging is effective for studying cooler regions, it cannot capture the full extent of the hot corona. “To study these high-temperature structures—especially miniature plasma loops—we need a combination of ground-based and space-borne instruments sensitive to multiple wavelengths, particularly in the UV and EUV bands.”
Jayant Joshi said that by using very fine filters, they could clearly see detailed structures. The bright areas in these images show spots where energy was strongly deposited, heating the plasma loops.
Implications for Coronal Heating and Solar Dynamics
Joshi also emphasised the role of density in coronal heating and said that the Sun’s outer atmosphere, the corona, has a much lower particle density than the underlying chromosphere, where these miniature loops are observed. Because of its higher density, the chromosphere is more difficult to heat efficiently. As a result, for the same amount of energy deposition, the corona experiences a greater temperature increase compared to the chromosphere.
“The surprising aspect of our study,” he continued, “is the discovery of small plasma loops that are not only highly localised and dense but also exhibit significant heating. This challenges conventional models and offers new insights into the mechanisms driving coronal heating, possibly involving magnetic reconnection or wave dissipation at fine spatial scales.”
Jayant Joshi explained the Differential Emission Measure (DEM) analysis in determining plasma temperatures within the solar loops. He clarified, "When we refer to the solar corona having a temperature of a million degrees, it doesn't imply uniformity across the entire plasma. In reality, the corona consists of plasma at a wide range of temperatures—some regions can be as hot as 10 million degrees Kelvin, while others may be as cool as half a million degrees. DEM analysis helps disentangle this complexity by measuring the intensity of emissions across various wavelengths, each corresponding to a different temperature range. This technique allows researchers to map the distribution of plasma temperatures within the corona, providing a more accurate and detailed understanding of the solar atmosphere's thermal structure."
These miniature loops also produce plasma jets and achieve extreme temperatures. When asked about the implications of detecting plasma jets associated with small plasma loops—and whether these findings suggest a common mechanism behind both small- and large-scale solar eruptions—Samanta explained that, as per observations, at any given moment, more than a million plasma jets may be present in the chromosphere. These jets, much like water spurting from a fountain, are narrow, fast streams of hot, charged particles that erupt from the Sun’s surface. “We observed plasma jets erupting upward from the tops of these loops.”
Interestingly, scientists have found that many of these jets are closely associated with miniature plasma loops, often originating from the same regions and appearing simultaneously. This co-occurrence raised intriguing questions for the research team, as it hints at a potentially shared origin or driving mechanism.
Joshi added that these plasma jets are significant not only because of their sheer number—millions are produced daily—but also because of their role in solar dynamics. These highly energetic plasma flows can escape the Sun’s gravitational pull and feed into the solar wind, the continuous stream of charged particles flowing outward through the solar system.
Scientists haven't yet fully figured out why plasma loops and jets form on the Sun, but they may be caused by the same process—magnetic reconnection. This process can help drive the solar wind, which affects Earth’s atmosphere, space weather, and satellite systems.
Adding further, Samanta explained that in this study, the researchers used a technique known as slit spectroscopy to analyse specific regions of the Sun. By placing a virtual slit—or drawing a line—across the solar surface using imaging instruments, they were able to obtain spectroscopic data along that line. This technique allowed them to measure key physical parameters such as plasma velocity (through Doppler shifts), temperature, density, and emission intensity at various points along the slit.
With the upcoming installation of the 2-metre National Large Solar Telescope (NLST) near Pangong Lake in Ladakh, Indian scientists are set to probe deeper into the Sun’s hidden layers and decode more of its magnetic mysteries. Joshi noted that if completed on schedule, NLST would be the largest solar telescope in Asia. While the telescope used in this study has a 1.6-meter primary aperture, a bigger telescope of 2 meters has been proposed with significantly higher resolution, which will enable scientists to study the fundamental structures of the solar atmosphere. He emphasised that such a facility is essential for advancing solar physics and pushing the frontiers of solar astronomy.
