Space-weather forecasters may have been missing part of some solar eruptions. A new study using observations from 17 spacecraft found that a coronal mass ejection, or CME, could contain a hotter and thinner component that is difficult to identify from Earth. In the case examined by the researchers, spacecraft near the eruption saw a different structure from the one that eventually travelled toward our planet.
CMEs are enormous clouds of magnetised plasma launched from the Sun. When one reaches Earth, it can disturb the planet’s magnetic field, trigger auroras, and interfere with satellites, radio communication, navigation systems, and electrical infrastructure. The danger depends less on the cloud’s appearance than on its speed, density, and magnetic orientation when it arrives.
The new study focused on an eruption observed in December 2024. NASA’s Europa Clipper spacecraft, then travelling through interplanetary space, recorded a solar-wind disturbance that was hotter and less dense than the material measured by other spacecraft. STEREO-A, positioned elsewhere in the Solar System, detected a faster and asymmetric part of the eruption that appeared to be directed toward Earth.
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From Earth’s viewpoint, that component was largely hidden. The solar eruption looked as though it had one structure, while the spacecraft spread across different positions measured several parts moving at different speeds and temperatures. The comparison shows why a single line of sight can produce a misleadingly tidy picture of an event that is changing as it crosses space.
The finding does not mean that every CME contains a concealed second cloud. It does show that a CME can be internally structured and that the pieces may separate as they travel. A forecast based on the first measurements near the Sun could therefore underestimate how quickly a later component will arrive or misjudge the conditions inside it.
That distinction becomes increasingly important as more spacecraft move away from Earth. Missions designed for planetary exploration are often treated as scientific observers of their destination, but their particle and magnetic-field instruments also create an accidental network of weather stations across the Solar System. Europa Clipper’s measurements offered a view that a dedicated Earth-facing monitor could not provide.
The researchers argue that future space-weather systems should combine observations from several locations rather than relying mainly on images and measurements taken near Earth. Better coverage would help forecasters track how an eruption changes with distance and identify the part most likely to interact with Earth’s magnetic field.
The geometry of the observations is central to the result. Two spacecraft can watch the same eruption from different angles and still record different temperatures, densities, and speeds because the cloud is expanding through a changing solar wind. A monitor near Earth may therefore measure the broad front of a CME while another spacecraft samples a narrower, faster stream embedded inside it. Treating either measurement as the whole event can hide the condition that matters most for forecasting.
The practical consequence is straightforward: a solar storm can be understood only in motion. The Sun launches the material, but its final effect depends on how the cloud expands, fragments, and reorganises during the journey. A wider spacecraft network will not remove the uncertainty, but it can show which parts of an eruption Earth is actually about to receive.
Curiosmos has previously examined what would happen to the Moon if Earth vanished and the hazards that would follow if GPS went dark. The new result adds a more immediate problem: before protecting technology from a solar storm, scientists must first know which part of the storm is on its way.
Sources
- Phys.org, 21 August 2026: Interplanetary spacecraft capture a coronal mass ejection Earth-based monitors missed
- Luspay-Kuti et al., *Science Advances* (2026), DOI: 10.1126/sciadv.aed9960
