Solar energetic particle events, or SEPs, are sudden surges in the population of electrons, protons, and heavy ions speeding through interplanetary space. They are widely understood to arise from particles accelerated by magnetic reconnection in solar flares and at shock waves that form ahead of fast CMEs. The most intense events can deliver radiation doses lethal to unshielded astronauts and can damage spacecraft electronics, which is why predicting them has become a priority as agencies prepare for sustained human missions to the Moon and Mars. For decades, forecasters have relied on space-based coronagraphs such as the Large Angle and Spectrometric Coronagraph on the Solar and Heliospheric Observatory, which images the corona only above roughly 2.3 solar radii from the Sun’s center. That limitation matters because the fastest SEP particles can reach Earth in a matter of tens of minutes, arriving before the parent CME has even entered the field of view of such instruments. By the time a space-based coronagraph confirms a fast eruption, the radiation event may already be underway.

The K-Coronagraph, installed at the 3,440-meter altitude Mauna Loa observatory in late 2013, was designed to close precisely this gap. As an internally occulted, ground-based instrument, it images the polarization brightness of the corona, produced by Thomson scattering of photospheric light off free electrons, in a near-infrared passband spanning 720 to 750 nanometers, and it does so starting at just 1.05 solar radii and extending to 3.0. Its 15-second cadence represented a dramatic improvement over the 3-minute cadence of its predecessors, the Mark-3 and Mark-4 coronameters, and a fully automated processing pipeline reduced data latency to 2.5 minutes, compared with as much as 24 hours previously. The pipeline includes an automatic CME detection algorithm that scans processed images and dispatches email alerts containing the eruption’s detection time, height, position angle, and speed, along with a “heartbeat” signal that tells forecasters the observatory is watching and sees nothing alarming.

To identify which of the roughly 600 CMEs detected by K-Cor since 2013 were accompanied by SEPs, the team drew on an updated catalog of events including protons of approximately 25 MeV observed by the High Energy Telescopes aboard the twin STEREO spacecraft and by instruments on near-Earth satellites such as SOHO’s Electron Proton Helium Instrument and Energetic and Relativistic Nuclei and Electron experiment. The combination proved powerful because of orbital geometry: at the start of K-Cor operations near the maximum of Solar Cycle 24, STEREO-B sat on the far side of the Sun, magnetically well connected to the Sun’s eastern limb, a region from which energetic particles are difficult to detect from Earth. After contact with STEREO-B was lost in October 2014, STEREO-A drifted into a similarly advantageous position. Of 215 individual SEP events catalogued during the study window, most occurred during the observatory’s daily data gaps, and in five cases K-Cor was observing but saw no CME, generally because the eruption was far from the plane of the sky where the instrument’s sensitivity falls off, or because elevated instrumental stray light degraded early observations. That left 27 confirmed SEP-associated CMEs.

The comparison with the control sample, drawn from a 2023 catalog of near-limb K-Cor events compiled by Song and colleagues, produced differences that were striking in their consistency. The average and median angular widths of the SEP-producing CME drivers were a factor of two larger than those of the non-SEP events, both in the inner corona and in the middle corona where space-based instruments took over. The average speed of SEP CMEs in the inner corona was more than twice that of their quiet counterparts, and nearly twice as fast in the middle corona. More than 80 percent of all the CMEs in both samples were accelerating as they climbed through the inner corona, but the average acceleration for the SEP events was almost a factor of three larger. Mass estimates from the Coordinated Data Analysis Workshops catalog, derived from LASCO brightness measurements, told the same story: the average SEP CME was nearly three times more massive than the average non-SEP event, with median masses of 8.7 times ten to the fifteenth grams versus 2.1 times ten to the fifteenth.

The study also found a possible new telltale signature in extreme-ultraviolet images from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly. Among 64 events whose low-coronal morphology could be classified, nine displayed what the authors call very hot flux ropes, structures visible only in the hottest coronal channels and often trailing the cooler erupting bubble by roughly 0.1 solar radii. Seven of those nine, or 78 percent, were associated with SEP events, making the hot flux rope one of the strongest indicators of an impending radiation storm, though the authors caution it is not a necessary one, since eight of the fifteen classified SEP CMEs lacked the feature. The team further tied CME kinematics to flare timing, showing directly that over 70 percent of CMEs in both samples stood below five solar radii at the moment of peak soft X-ray flux, a relationship previously established only through extrapolation, and one that SEP prediction models may be able to exploit.

Perhaps the most operationally significant number in the study is 28 minutes. That is the average interval between K-Cor’s first detection of an SEP-associated CME and LASCO C2’s first detection of the same event, a head start delivered before any accounting of the hours of telemetry latency that can delay space-based imagery. K-Cor’s 84 percent detection rate of SEP CMEs occurring during its observing windows, 27 of a possible 32, was commensurate with the 92 percent rate achieved by the earlier Mk3 and Mk4 instruments over three decades. Only one of the 27 associated SEP events registered at the S1 level on NOAA’s solar radiation storm scale in the near-Earth environment, and three more would have exceeded that threshold as measured by STEREO-A far from Earth, but the authors note that the K-Cor era coincided with unusually weak solar activity, with only ten CMEs exceeding 1,800 kilometers per second compared with 37 in an equivalent span during the Mark-4 era. The Sun has produced 80 percent more fast CMEs in the less than three years since the 2022 hiatus than during the nine years of K-Cor observations themselves.

The timing of this work could hardly be more pointed. SOHO, launched three decades ago, will eventually be decommissioned, and its CME monitoring role is passing to NOAA’s new Compact Coronagraphs. CCOR-1, launched in June 2024 aboard GOES-19, and CCOR-2, launched in September 2025 on the Space Weather Follow-On mission now stationed at the Lagrange 1 point, both begin their fields of view at 3.5 solar radii or beyond, image every 15 minutes, and require a second image before a speed can be computed. The authors’ arithmetic is sobering: for a CME traveling at the study’s average SEP-associated speed of just over 800 kilometers per second, a 25 MeV proton following the nominal Parker spiral path reaches 1 astronomical unit in about 43 minutes, meaning the radiation event would already be underway by the time a CCOR speed estimate became available. Higher-energy particles, the ones that matter most for aviation and human spaceflight, arrive even sooner.

With Mauna Loa’s access road repaired, routine K-Cor observations resumed on March 31, 2026, and the instrument once again feeds near-real-time alerts to NASA’s Community Coordinated Modeling Center SEP Scoreboard. The study’s authors are careful to acknowledge the limitations of a single ground-based observatory, hemmed in by weather, daylight, staffing, and geography, and their sample excludes the rare, most extreme events simply because none occurred during an observing window. Yet their conclusion is unambiguous: ground-based coronagraphy, with its low observational threshold, rapid cadence, and 2.5-minute data latency, offers a warning capability that no current or planned space-based instrument can match on its own, and the distinctive properties of SEP-producing eruptions in the inner corona, their greater width, speed, acceleration, and mass, provide forecasters with physical signatures to watch for. As humanity prepares to send crews beyond Earth’s protective magnetosphere, the view from a mountaintop in Hawaii may prove to be one of the best early-warning systems available.

Coronal mass ejections, or CMEs, are enormous clouds of magnetized plasma expelled from the Sun during violent eruptions. When directed toward Earth, they can trigger geomagnetic storms capable of disrupting satellites, radio communications, navigation systems and electrical grids. The most powerful events can induce currents in long-distance power infrastructure and interfere with spacecraft operations. Yet predicting exactly when a CME will arrive remains difficult because conventional solar observatories often lose sight of the eruption while it is still far from Earth.

PUNCH is designed to close that observational gap. Its four small spacecraft, launched on March 11, 2025, operate together as a single distributed observatory spanning roughly 8,000 miles. Three spacecraft carry SwRI-developed Wide Field Imagers, while the fourth carries a narrower-field instrument focused closer to the Sun. Working in coordination, the spacecraft observe the solar corona and the emerging solar wind as one connected system rather than treating the Sun’s outer atmosphere and interplanetary space as separate regions.

“Forecasting exactly when a CME will arrive is difficult because many conventional solar cameras often lose sight of the cloud long before it reaches us,” said Craig DeForest, a SwRI scientist, PUNCH principal investigator and lead author of the study. “The SwRI-developed and -led Wide Field Imagers aboard three of the four PUNCH spacecraft are collecting high-resolution images of entire CMEs over most of their trajectory, in greater detail than previously possible.”

The mission’s first fast, Earth-directed CME arrived in late May 2026, providing an important test of PUNCH’s capabilities. The eruption was tracked across approximately nine-tenths of the distance between the Sun and Earth. Rather than relying solely on measurements taken near the Sun and extrapolating the CME’s later motion, researchers followed the expanding front directly through a large portion of interplanetary space. That continuous view gave them information about the eruption’s changing size, direction and speed as it traveled.

To demonstrate the forecasting potential, the scientists used a deliberately simple geometric representation known as the “ice cream cone model.” In this model, the tip of the cone indicates the region on the Sun where the CME originated, while the broad, rounded top represents the expanding cloud of plasma. Although real CMEs can have complex structures and irregular magnetic fields, the simplified model captures essential characteristics of the eruption’s outward motion and expansion.

Researchers manually traced the bright outer edge of the CME in successive PUNCH images collected during May. They then adjusted only three primary geometric parameters to determine how the cloud evolved over time and where its leading edge would intersect Earth’s orbital position. The resulting forecasts, produced retrospectively after the event, identified the CME’s arrival within a 30-minute interval eight hours before the impact. That level of precision is roughly ten times better than the performance currently associated with many forecasting approaches based primarily on coronagraph observations near the Sun.

The result is especially significant because the researchers did not use an elaborate numerical simulation of the solar wind or a detailed reconstruction of the CME’s magnetic structure. Instead, they applied a basic model to unusually comprehensive observations. As additional PUNCH images became available, the predicted arrival time converged and became more stable. The study therefore suggests that better data coverage may be at least as important as greater model complexity when scientists are trying to determine when a solar storm will reach Earth.

The approach could eventually improve warnings for satellite operators, aviation networks, communications providers and electric utilities. A more reliable estimate of a CME’s arrival time would give organizations additional opportunity to place spacecraft in safe operating modes, adjust satellite operations, protect vulnerable electrical equipment and prepare for disruptions to high-frequency radio and navigation signals. Forecasting the direction and strength of an impact remains a separate challenge, however, because the magnetic orientation of a CME strongly influences how severely it interacts with Earth’s magnetosphere.

PUNCH’s broader scientific purpose is to understand how the corona transitions into the solar wind, the continuous stream of charged particles flowing outward from the Sun. By observing that transition and following large-scale structures through the heliosphere, the mission provides a wide-angle view of the environment surrounding Earth. The new study indicates that this perspective may also have immediate practical value. What began as a mission designed to investigate fundamental solar physics could become an important component of future space weather forecasting, turning distant images of solar eruptions into actionable warnings before they reach our planet.

Subject of Research: Improving coronal mass ejection arrival-time forecasting through wide-field space-based imaging.

Article Title: PUNCH Mission Demonstrates More Precise Forecasting of Coronal Mass Ejection Arrivals

News Publication Date: August 4, 2026

Web References: https://www.swri.org/markets/earth-space/space-research-technology/space-science/heliophysics ; https://youtu.be/Qqtakkfo-mg

Image Credits: Southwest Research Institute

Keywords

PUNCH mission, NASA, Southwest Research Institute, coronal mass ejections, CME forecasting, space weather, solar storms, heliosphere, solar wind, geomagnetic storms, satellite protection, Sun-Earth system

After a successful journey to Vandenberg Space Force Base in California, PUNCH’s four suitcase-sized satellites have reached their final Earth-side destination before embarking on an ambitious journey into polar orbit. The collaborative launch, shared with NASA’s SPHEREx mission, is scheduled for late February 2025, marking a significant milestone in heliophysics. With a strategic deployment along the day-night line, these satellites are designed to remain in sunlight, ensuring optimal operational conditions for their scientific instruments.

Principal Investigator Dr. Craig DeForest, leading the PUNCH mission from SwRI’s Solar System Science and Exploration Division, emphasized the significance of this mission. PUNCH aims to bridge the understanding of two crucial solar phenomena: the solar corona, the outer atmosphere of the Sun visible during eclipses, and the solar wind—the stream of charged particles extending throughout the solar system. This real-time measurement of the solar environment will enhance our predictive capabilities regarding solar weather events and their potential impacts on Earth.

As the constellation prepares for launch, it is equipped with an array of sophisticated instruments designed to capture unprecedented data. Three of the satellites will feature Wide Field Imagers (WFIs), developed to provide detailed heliospheric imagery from notable distances away from the Sun. These innovative instruments utilize specialized baffles and an artificial horizon to filter out overwhelming brightness from the Sun, akin to aiming a telescope at a distant star without being blinded by its light.

The significance of the WFIs lies in their ability to detect faint light emitted by the solar corona and the solar wind. Solar phenomena, such as coronal mass ejections, have far-reaching effects on space weather and can disrupt satellite communications and power grids on Earth. By gaining insight into these events, scientists can better forecast their trajectories and impacts, enhancing our preparedness for solar storms.

In addition to the WFIs, PUNCH includes a fourth satellite equipped with a Narrow Field Imager—a sophisticated coronagraph created by the U.S. Naval Research Laboratory. This instrument continuously captures detailed images of the solar corona, providing vital information on the dynamics and structure of this elusive solar atmosphere. The combined efforts of these four spacecraft will generate a wealth of data, synchronizing their observations to function as a singular, virtual instrument with a comprehensive field of view.

To make sense of the polarized light reflected off of solar particles, each PUNCH satellite features advanced imaging capabilities. These include a camera system developed by RAL Space, which captures images through three distinct polarizing filters. This innovative technique allows scientists to construct a three-dimensional map of solar phenomena within the corona and throughout the inner solar system.

The notion of polarized light aligns perfectly with ambient phenomena such as sunlight scattering. As sunlight interacts with charged particles in the solar wind, it becomes polarized, granting scientists insight into the characteristics and movement of the corona. The ability to analyze these polarized light patterns marks a significant improvement over traditional imaging methods that lack measurements for three-dimensional motion. With PUNCH’s innovative approach, researchers stand to enhance their understanding of how these solar features behave and evolve over time.

The path to this launch has not been without challenges. PUNCH Project Manager Ronnie Killough noted the resilience of the team in overcoming late-breaking hurdles during the mission’s integration and environmental testing phases. Each member of the team demonstrated exceptional adaptability, ensuring that the spacecraft were ready for the rigors of launch and the harsh conditions of space. The anticipation surrounding the launch only amplifies the excitement for the data that will soon flow back to Earth.

PUNCH is part of NASA’s Small Explorers (SMEX) program, which promotes innovative scientific missions that seek to answer fundamental questions about space and solar phenomena. SwRI’s leadership in the PUNCH mission serves as a testament to its commitment to advancing heliophysics and astrophysics research through innovative approaches. Collaborating with esteemed partners such as the U.S. Naval Research Laboratory and RAL Space highlights the collective effort required to realize such ambitious scientific goals.

As the countdown to launch continues, the PUNCH mission promises to deliver profound advancements in our understanding of the Sun’s behavior, thereby enhancing our predictive capabilities regarding solar weather and its associated effects on terrestrial systems. As we seek to untangle the complexities of the solar system and its interactions, PUNCH stands poised to illuminate the path ahead, revolutionizing our approach to solar dynamics and offering fresh insights into the forces that shape our cosmic neighborhood.

For those eager to learn more about this exciting mission and the scientific endeavors it encompasses, further information can be found on the official website dedicated to PUNCH and its various components. The opportunity to contribute to the study of solar phenomena marks a thrilling chapter in the field of space science, and with PUNCH, we stand on the brink of discovery.

Subject of Research: Polarimeter to Unify the Corona and Heliosphere (PUNCH)
Article Title: PUNCH Mission Prepares for Launch: A New Chapter in Solar Exploration
News Publication Date: January 22, 2025
Web References: https://www.swri.org/heliophysics
References: N/A
Image Credits: USSF 30th Space Wing/Alex Valdez

Keywords

: Solar research, PUNCH mission, heliophysics, solar corona, solar wind, spacecraft, NASA, space weather, coronal mass ejections, imaging technology, scientific collaboration, cosmic phenomena.