Tiny Plasma Loops in Sun’s Lower Atmosphere Unveil New Magnetic Mysteries

In a remarkable new discovery that could reshape our understanding of the Sun’s atmospheric dynamics, a team of astronomers has observed miniature plasma loops hidden within the lower layers of the Sun’s atmosphere. These structures, previously invisible due to their tiny size and fleeting lifetimes, are now offering unprecedented insights into one of solar physics’ greatest puzzles: how magnetic energy is stored and explosively released in the Sun’s atmosphere.

The breakthrough comes from a collaborative effort led by researchers at the Indian Institute of Astrophysics (IIA), an autonomous institution under India’s Department of Science and Technology (DST), alongside international partners from NASA, the Max Planck Institute for Solar System Research (Germany), and the Big Bear Solar Observatory (USA). Their findings are detailed in a recent publication in The Astrophysical Journal.

Plasma Loops: Hidden in Plain Sight

While the Sun appears placid to the naked eye, it is a roiling sphere of ionized gas or plasma, shaped by powerful magnetic fields. These fields sculpt arc-like structures known as coronal loops in the Sun’s outer atmosphere—the solar corona—which glow brightly at temperatures over a million degrees Celsius.

However, below this highly dynamic layer lies a more obscure realm: the chromosphere, just above the Sun’s visible surface. It is here that scientists have now detected miniature counterparts of the large coronal loops—mini loops measuring only about 3,000 to 4,000 kilometers long (comparable to the distance between Kashmir and Kanyakumari) and less than 100 kilometers wide. These loops, difficult to detect due to their scale and brief lifespans—often just a few minutes—have finally been imaged and studied using multi-instrument, high-resolution observational techniques.

How the Discovery Was Made

The team employed a synergy of advanced instruments, including the Goode Solar Telescope (GST) at Big Bear Solar Observatory, NASA’s Interface Region Imaging Spectrograph (IRIS), and the Solar Dynamics Observatory (SDO). This ensemble allowed them to study the loops across the visible, ultraviolet (UV), and extreme-ultraviolet (EUV) spectrum—each probing different layers of the Sun's atmosphere.

Annu Bura, a Ph.D. researcher at IIA and the lead author of the study, remarked:

“These tiny loops live fast and die young, but they offer a profound window into the microphysics of the Sun’s magnetic activity.”

The loops were particularly visible in the H-alpha spectral line—a signature emission from hydrogen atoms—where they appeared as bright, arching filaments in the chromosphere. Data from IRIS also revealed dramatic broadening of spectral lines, an indication of non-thermal processes and magnetic activity.

The Magnetic Reconnection Puzzle

One of the most striking features observed was the eruption of plasma jets from the tops of these miniature loops. These jets, according to Tanmoy Samanta, faculty at IIA and co-author of the study, are likely caused by magnetic reconnection—a process where twisted magnetic field lines suddenly realign, releasing large amounts of energy.

“Both the jets and the loops seem to originate from the same magnetic explosion. This mirrors larger events seen in the corona, suggesting a universal mechanism operating across scales,” said Samanta.

The researchers also noted similarities to large-scale coronal jets, indicating that even these miniature loops may play a role in larger solar phenomena such as solar flares and space weather effects that influence Earth.

Million-Degree Mystery in the Chromosphere

A central puzzle emerged when the team measured the plasma temperatures inside these loops. Using a technique known as Differential Emission Measure (DEM) analysis, they found that some of these loops reached temperatures exceeding several million degrees—extremely hot for structures situated within the dense chromosphere.

“Heating such dense plasma to that temperature should be very difficult,” said Jayant Joshi, another IIA faculty member and co-author. “This observation challenges current models of chromospheric heating. Future spectroscopic studies are essential to understand this anomaly.”

Looking to the Future: NLST and Beyond

The discovery points to the next generation of solar exploration. India’s upcoming National Large Solar Telescope (NLST), a 2-meter class solar telescope planned near Pangong Lake in Ladakh, is expected to revolutionize high-resolution chromospheric imaging and magnetic diagnostics. With this telescope, scientists hope to uncover even finer structures and deeper mechanisms behind solar magnetism.

By revealing these tiny yet powerful loops, the current study represents a critical leap in our understanding of small-scale solar activity, and how it may cascade into larger, more impactful events in the heliosphere. It also underscores the value of international collaboration, combining ground-based and space-borne telescopes to resolve solar phenomena down to the smallest scale yet observed.

As researchers continue to peel back the layers of our nearest star, each discovery of small-scale solar activity helps complete the puzzle of how energy flows and explodes in the Sun’s atmosphere — phenomena that, despite their astronomical distance, can influence satellites, communications, and even power systems on Earth.