The U.S. National Science Foundation (NSF) Daniel K. Inouye Solar Telescope, the world’s most powerful solar telescope, designed, built, and operated by the NSF National Solar Observatory (NSO), achieved a major breakthrough in solar physics by directly mapping the strength of the magnetic field in the solar corona, the outer part of the solar atmosphere that can be seen during a total eclipse. This breakthrough promises to enhance our understanding of space weather and its impact on Earth’s technology-dependent society.
The Corona: The Launch Pad of Space Weather
The Sun’s magnetic field generates regions in the Sun’s atmosphere, often rooted by sunspots, that store vast amounts of energy that fuel explosive solar storms and drive space weather. The corona, the Sun’s outer atmosphere, is a superheated realm where these magnetic mysteries unfold. Mapping coronal magnetic fields is essential to understanding and predicting space weather — and to protect our technology in Earth and space.
Why It Matters
Earth’s magnetic field shields us from solar winds, protecting our atmosphere, and making life possible. However, the electromagnetic fields and energetic particles from extreme solar eruptions can disrupt satellites, power grids, and other systems we need in our increasingly technological society. Understanding these dynamic interactions, which change on timescales ranging from days to centuries, is crucial for safeguarding our infrastructure and current way of life.
Measuring the corona’s magnetic properties has long challenged astronomers and the limits of technology. Today, the Inouye Solar Telescope is the most advanced facility designed to study the corona, and has made a crucial first step in resolving these mysteries by producing its first coronal magnetic field maps — the most detailed to date.
The Inouye Solar Telescope’s First Maps of the Corona’s Magnetic Field
Since the 1950s, solar physicists have mapped the magnetic fields on the Sun’s surface, providing valuable insights. However, maps of the magnetic field in the zones above the surface, like the corona, have long been sought as it is in these locations that solar storms originate. The Inouye, located near the summit of Maui’s Haleakal? in Hawai’i, now provides the capabilities to meet this critical need.
The Inouye has created its first detailed magnetic field maps of the solar corona using the Zeeman Effect, which measures magnetic properties by observing spectral line splitting. Spectral lines are distinct lines that appear at specific wavelengths in the electromagnetic spectrum, representing the light absorbed or emitted by atoms or molecules. These lines act like “fingerprints,” as they are unique to each atom or molecule, allowing scientists to identify the chemical composition and physical properties of celestial objects by looking at their spectra. When exposed to a magnetic field, like in the Sun, these lines split, which gives us an insight into the object’s magnetic properties. Previous attempts at detecting these signals, last reported two decades ago (Lin et al. 2004), lacked the detail and regularity needed for extensive scientific investigation. Today, the Inouye’s unmatched capabilities allow for detailed, regular studies of these crucial signals.
Technological Marvel
Typically, one can only view the Sun’s corona — a region one million times fainter than the solar disk — during a total solar eclipse, when most of the Sun’s light is blocked and Earth’s sky goes dark. The Inouye, however, uses a technique called coronagraphy to create artificial eclipses, allowing it to detect extremely faint polarized signals — a billion times fainter than the solar disk — highlighting its unparalleled sensitivity and solidifying its status as a unique window to our home star.
The Inouye accomplishes this with its Cryogenic Near-Infrared Spectropolarimeter (Cryo-NIRSP), one of the telescope’s primary instruments used to study the corona and map its magnetic fields. This instrument was designed and built by the University of Hawai’i Institute for Astronomy.
Future Prospects
This milestone marks the beginning of a new era in solar physics. The Inouye’s success in mapping the Sun’s coronal magnetic fields reaffirms its vision and mission, and opens new frontiers in understanding the Sun’s influence on space weather.
“Just as detailed maps of the Earth’s surface and atmosphere have enabled more accurate weather prediction, this thrillingly complete map of the magnetic fields in the sun’s corona will help us better predict solar storms and space weather,” says Dr. Carrie Black, NSF program director for the NSO. “The invisible yet phenomenally powerful forces captured in this map will propel solar physics through the next century and beyond.”
Christoph Keller, NSO Director, remarks that “Mapping the strength of the magnetic field in the corona is a fundamental scientific breakthrough, not just for solar research, but for astronomy in general.” He anticipates that “This is the beginning of a new era where we will understand how the magnetic fields of stars affect planets, here in our own solar system and in the thousands of exoplanetary systems that we now know about.”
Ongoing and future studies will refine diagnostic tools and techniques, leading to deeper insights into the Sun’s magnetic environment and its impact on Earth and our solar system.