At times, the sun ejects energetic material into space, a phenomenon that can have significant consequences for both space-based and ground-based electronic technology. Researchers are striving to understand this phenomenon and develop ways to forecast it, including how the ejected material evolves as it travels through the solar system. For the first time, researchers, including those from the University of Tokyo, have made high-quality measurements of an evolving cloud of solar ejecta using multiple space-based instruments not originally designed for this purpose. They observed how these clouds reduce background cosmic-ray activity.
Solar storms, known as coronal mass ejections (CMEs), are surprisingly common. When detected near Earth, some satellites are even put into a safe, low-power mode until the storm passes to protect them. However, as with more familiar terrestrial weather, it is the events that cannot be prepared for that often cause the most damage. To mitigate this, researchers are attempting to understand how CMEs evolve as they move away from their source, the sun. A new method, which pools the resources of several scientific satellites, could lead to improved space-weather forecasting.
Innovative Approach to Understanding CMEs
“Understanding how huge clouds of solar material travel through space is essential for protecting satellites, astronauts, and even power grids on Earth,” said Ph.D. researcher Gaku Kinoshita from the Department of Earth and Planetary Science.
In our new paper, we show that the paths of these solar eruptions can be tracked using drops in cosmic rays, high-energy particles that constantly bombard the solar system, measured by spacecraft.
By combining observations from several spacecraft at different locations, researchers were able to observe how one eruption changed shape and strength as it moved away from the sun, revealing new ways to improve space-weather forecasting.
The researchers’ method leverages an effect known as the Forbush decrease, which describes how a CME isn’t perfectly transparent to cosmic rays coming from behind it. This is due to the CME’s strong magnetic field, which can deflect charged particles like cosmic rays. By observing cosmic rays as a CME passes through a region, the team could interpret the physical makeup of the CME and, crucially, how it changes over time.
Collaborative Observations and Unexpected Discoveries
In March 2022, three spacecraft — the European Space Agency (ESA)’s Solar Orbiter, ESA and Japan Aerospace Exploration Agency (JAXA)’s BepiColombo, and NASA’s Near Earth Spacecraft — were ideally positioned to observe the same solar eruption from different locations in space. This rare alignment allowed researchers to compare how the event appeared from different directions and distances from the sun. “By combining cosmic-ray data with magnetic-field and solar-wind measurements, we could link changes in the particle signal directly to the physical structure of the eruption,” noted Kinoshita.
One of the most significant findings of this work is the realization that instruments never designed for scientific purposes can still deliver valuable data. A simple system-monitoring instrument onboard the BepiColombo spacecraft, originally intended only to maintain spacecraft health, was calibrated to detect cosmic-ray decreases. This data, previously overlooked, proved too valuable to waste.
Implications for Future Space-Weather Forecasting
While there are advanced instruments capable of directly monitoring CMEs, their operational periods are limited. In contrast, the approach described here repurposes more general instruments that are always active, allowing for continuous data collection. Researchers can enhance data quality by combining information from multiple spacecraft, which is crucial for constructing a 3D picture of CMEs.
“Because the instruments used were never intended for scientific research, there was no existing framework to rely on. We had to evaluate an instrument’s behavior, calibrate it from scratch, and develop new analysis methods ourselves before we could confidently use the data to study cosmic-ray decreases,” Kinoshita explained.
With many spacecraft now operating between the sun and Earth, and more planned for the future, the chances of making routine multipoint observations are increasing.
If researchers continue to combine data from multiple missions and utilize all available instruments, a more comprehensive understanding of how solar ejections propagate through space can be achieved.
This development represents a significant step forward in the ability to forecast solar weather, potentially safeguarding technology and infrastructure from the unpredictable effects of solar storms. As the research community continues to refine these methods, the potential for mitigating the impacts of CMEs on Earth grows ever more promising.
