When a spacecraft passes through a coronal mass ejection, how well can researchers reconstruct the properties of the event from the data collected along the way? New modeling explores the impact of spacecraft trajectory on the inferred properties of coronal mass ejections.
Considering Coronal Mass Ejections
Each year, the Sun unleashes hundreds of coronal mass ejections (CMEs): eruptions of plasma and magnetic fields from the Sun’s upper atmosphere, or corona. These massive events unfurl from the solar corona and sweep through our solar system, producing potentially destructive geomagnetic storms when they strike Earth.
CMEs are thought to start out as twisted magnetic fields called flux ropes, but matching the predictions of this theory to observations of CMEs is difficult. When viewing an eruption from afar, the complex three-dimensional structure of a CME is flattened into two dimensions. Sending one or more spacecraft through a CME offers a complementary perspective, capturing the CME’s behavior along the spacecraft’s path. In this case, we’re generally limited to a few trajectories — at best — through the CME. How well can researchers extrapolate the properties of the CME from information gleaned from a spacecraft’s flight?
Synthetic Space Travel
Projected locations of synthetic spacecraft in each model run. [Palmerio et al. 2026]
The team focused on two of their simulations, which differed in terms of the complexity of the magnetic field from which the CME emerged; in one model run, the magnetic field had a bipolar configuration, while in the other, the configuration was quadrupolar.
The team sent a fleet of 100 digital spacecraft into these CMEs, each viewing the passage of the CME from a different radial distance, latitude, and longitude. To focus entirely on the intrinsic properties of the CME, the team kept the surroundings simple, allowing their synthetic CMEs to evolve against a nearly uniform solar wind background.
Scaled magnetic field strength for the CMEs arising from bipolar (Run A, top) and quadrupolar (Run B, bottom) source regions. [Palmerio et al. 2026]
CMEs with a Twist
Palmerio and coauthors found that the inferred properties of the flux rope depended strongly on the trajectory of the spacecraft through the CME. The inferred flux ropes differed in terms of their orientations, physical properties, and the direction that the magnetic field lines twist. This might help to explain certain puzzling CMEs for which the twist direction suggested by the source region didn’t match the direction inferred from spacecraft measurements.
In addition to these physical properties, the team also found differences in the performance of their fitting algorithm; in general, the farther the spacecraft’s trajectory from the axis of the flux rope, the worse the algorithm’s performance.
Though this investigation revealed challenges in interpreting the properties of a CME from spacecraft measurements, it also suggested that spacecraft observations may help to illuminate the magnetic field configuration of a CME’s source region. The modeled CME emerging from the quadrupolar source region experienced more magnetic reconnection with the surrounding solar wind, leading to lower overall magnetic field strength on the fringes of the ejected plasma, while the CME arising from the bipolar region showed more evidence of fast-moving outflows in its wake.
Citation
“On the 3D Magnetic Structure of Coronal Mass Ejections Through the Solar Corona,” Erika Palmerio et al 2026 ApJS 286 74. doi:10.3847/1538-4365/aea6be