Solar storms that fling magnetism across the solar system can knock out satellites, power grids, communication and navigation systems, and endanger astronauts in space. Scientists can observe these phenomena, called coronal mass ejections (CMEs), as they happen, but it’s difficult to predict when they will strike.

The Coronal Solar Magnetism Observatory (COSMO) could change that.

Scientists at the U.S. National Science Foundation National Center for Atmospheric Research (NSF NCAR) are developing COSMO to address the need for more advance warning of CMEs heading towards our planet. The ground-based solar observatory would transform humanity’s fundamental understanding of the formation of solar eruptions and other space weather that can affect technologies – and therefore the lives and livelihoods of people – on Earth.

With funding from the U.S. National Science Foundation, NSF NCAR has completed important milestones in COSMO’s development over the past year. In April, the team completed the Final Design Review (FDR) for the Large Coronagraph (COSMO-LC), the solar telescope that will be the central, most recognizable instrument at the observatory. They also narrowed the number of potential locations for COSMO and deployed instruments for the next phase of evaluations.

“We know solar storms brew in the Sun’s outer atmosphere, known as the corona, but we need to understand more about the magnetic processes and conditions that occur before a storm,” said Holly Gilbert, COSMO principal investigator and director of NSF NCAR’s High Altitude Observatory. “COSMO would measure the magnetic fields that drive the eruptions and allow us to study the solar atmosphere as an interconnected system – something no existing facilities or instruments can provide. It’s designed to fill important gaps in humanity’s observational capabilities.”

Final Design Review complete
NSF NCAR worked with European Industrial Engineering (EIE) on the final design review (FDR), completed in April 2025. The FDR represented the culmination of the efforts of NSF NCAR scientists, engineers, and their EIE partners to iterate and arrive at a COSMO-LC design that meets all scientific and technical requirements. As part of the FDR, EIE also developed a construction cost for the COSMO-LC telescope, the most uncertain COSMO cost element prior to FDR. The construction estimate is $20 million in fiscal year 2025 dollars, excluding site-specific costs for the telescope dome, instruments, and observatory buildings.

The COSMO-LC will have a 1.4-meter-diameter (55-inch) aperture, the opening in the lens that lets light in. This would make the coronagraph the largest diameter refracting telescope in the world. COSMO’s large aperture will allow the telescope to gather enough light to measure the strength of the corona’s magnetic field.

Three potential COSMO sites
After assessing six potential sites for COSMO, NSF NCAR has narrowed its focus to the following locations:

• Magdalena Ridge Observatory, New Mexico
• Cerro Tololo Inter-American Observatory, Chile
• Teide Observatory (Izaña), Spain

The team’s evaluation criteria included local cost drivers, scientific viability, geopolitical conditions, and other considerations.

For the next phase of site assessments, NSF NCAR has deployed additional instruments to measure atmospheric conditions that can affect the clarity of coronal observations while continuing to observe sky brightness and weather. NSF NCAR will continue working with communities at the three sites as data assessment continues. During this period, NSF NCAR will also refine data on construction cost drivers and other factors that will affect the choice of a COSMO site.

Following this phase, NSF NCAR will recommend a primary and backup site for COSMO and seek opportunities to propose for full construction of COSMO.

NSF NCAR will continue to collect weather and radiometric data at Barcroft Station in California and Observatorio Astronómico Félix Aguilar in Argentina, even though they weren’t selected for Phase 2 evaluation. The data may be useful for future projects, including coronagraph locations for the next generation Global Oscillations Network Group (ngGONG), which was the top recommendation for major research facility funding in the Solar and Space Physics Decadal Survey.

Filling a “critical information gap”
Right now, scientists can only see solar storms occurring – like spotting a fully formed tornado. COSMO would allow scientists to understand what’s happening in the Sun’s atmosphere before a solar storm, which is critical to the ability to predict when they will happen. Better predictions  would give power grid operators, satellite providers, and others more time to prepare for the coming solar storm, similar to issuing a tornado watch or warning.

COSMO will have three instruments working together to track energy buildup in the Sun’s magnetic field: COSMO-LC, the K-Coronagraph (K-Cor), and the Chromospheric and prominence Magnetometer (ChroMag). Together, these three instruments will observe changes in plasma conditions in the corona and the atmosphere just below the corona, which is called the chromosphere. These observations will be used to identify and track the physical processes that create solar storms and provide new information for space weather forecasting. The combination of the COSMO-LC, K-Cor, and ChroMag will be able to address multiple science objectives to provide the fundamental information required to predict space weather in the near future and 10 years out.

The information provided by COSMO will fill a “critical information gap” in science and space weather prediction capabilities, according to the Solar and Space Physics Decadal Survey, a comprehensive vision to advance and expand the frontiers of solar and space physics for the next decade.

The survey notes that “capturing eruptive phenomena will almost certainly require a global field of view” such as the COSMO-LC would provide. The survey also recognizes the COSMO-LC’s advanced state of design and that the observatory would incorporate proven technology, reducing the cost and scientific risks associated with construction. The Upgraded Coronal Multi-channel Polarimeter (UCoMP), currently in use at NSF NCAR’s Mauna Loa Solar Observatory (MLSO) in Hawaii, is a prototype for the larger COSMO-LC. K-Cor is already in use at MLSO, and ChroMagis ready to be deployed there. NSF NCAR also has more than 60 years of synoptic images from MLSO, allowing scientists to study coronal magnetic activity on short- and long-term time scales.

Studying the corona
Coronal study is at the heart of space weather prediction. COSMO would build on the capabilities of MLSO to create an even more comprehensive view of the corona and complement other available ground- and space-based observatories such as the NSF Daniel K. Inouye Solar Telescope, which sees solar phenomena three times smaller than any other solar telescope, or NASA’s Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission, launched in March 2025, which studies solar transient phenomena as they move from the corona to the Earth.

“The different observations, fields of view, and vantage points in space and on Earth allow us to create a more comprehensive view and understanding of the Sun,” said Sarah Gibson, NSF NCAR Senior Scientist and COSMO development lead. “COSMO would provide the missing piece, which is the global (whole Sun) view of the corona.”

About COSMO
COSMO-LC requires a large aperture to gather enough light to measure the strength of the corona’s magnetic field. Scientists will be able to observe visible and infrared light to see changes in the coronal magnetic field and plasma conditions. COSMO-LC is a coronagraph, where a small disc in the telescope called an occulter blocks the brightest part of the Sun to simulate an eclipse and allow scientists to study the corona. COSMO-LC will complement existing solar telescopes and address the critical, unfulfilled need to measure the energy stored in the corona’s magnetic field.

K-Cor, another coronagraph that is currently used at MLSO, observes visible or “white” light to track CMEs and provide information on the density of the corona. K-Cor is the only instrument in the world providing white light coronal images that include the low and middle corona. It captures images every 15 seconds, the highest cadence white light images available, which allows K-Cor to measure the rapid acceleration of fast-moving CMEs most likely to significantly affect the Earth. K-Cor generates automated alerts when it detects in-progress CMEs in their early stages of formation; these alerts are issued 25-90 minutes before the CME is visible in space-based coronagraph images (times include data latency), providing more time to protect important facilities on Earth as well as astronauts and satellites in space.

ChroMag will measure the magnetic field and plasma conditions in the atmosphere just below the Sun’s corona in the chromosphere. ChroMag will bridge observations of the visible surface of the sun, known as the photosphere, to those of the corona. ChroMag observations provide diagnostics of magnetic field, temperature, and velocity. These can be used with observations from the other COSMO instruments to connect the early formation of CMEs with energy buildup in the chromosphere and corona.  
 

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