Solar electrons can bounce off magnetic walls in space and race back toward Earth in reverse order.
April 29, 2026
Original Paper
Solar Energetic Particle Reflection by Precursor ICMEs: Multi-spacecraft Observations of Bi-Directional Electron Beams at 1 AU
arXiv · 2604.25019
The Takeaway
Energetic particles from the sun were observed reflecting off the shock front of a passing coronal mass ejection. This creates a strange inverse signal where the fastest electrons arrive last, which is the exact opposite of what usually happens. This reflection turns the space between the sun and Earth into a giant cosmic mirror for radiation. It identifies a significant and previously unknown radiation hazard for astronauts traveling to the Moon or Mars. Space weather forecasters will need to account for these back-splashing particles to keep future deep-space missions safe.
From the abstract
We present case studies of two impulsive solar energetic electron (SEE) events during which particles at energies from 1-600 keV were detected by THEMIS-ARTEMIS orbiting the Moon, Wind at Earth's first Lagrange point, and (for one event) STEREO-A located at 1 AU, off the Sun-Earth line. The SEEs were initially highly anisotropic, traveling outward along the magnetic field with distinct energy-time dispersion. For one event, the spectra contained inverse velocity dispersion (IVD) signatures, wher