Stellar plasma scattering (also: near-source signal broadening) refers to the frequency broadening of radio signals by stellar wind plasma turbulence and coronal mass ejections near the transmitting planet — before those signals travel through interstellar space. It is distinct from interstellar scintillation, which occurs along the propagation path between stars.
Discovery and Quantification
Identified and quantified by vishal-gajjar and grayce-c-brown at the seti-institute in a 2026 Astrophysical Journal paper (see src-plasma-technosignature-scattering-2026). The team calibrated the broadening effect using empirical data from solar system spacecraft tracking, then extrapolated across stellar environments.
Key Findings
- Stellar plasma near the source can “smear” an ultra-narrow narrowband radio signal’s frequency, reducing its peak power and causing it to fall below standard seti detection thresholds.
- Most seti pipelines account for interstellar propagation but overlook near-source plasma distortion.
- m-dwarf-stars (~75% of Milky Way stars) are highest-risk due to elevated stellar wind and CME activity.
- The effect may partly explain the radio silence seen in technosignatures surveys.
Implications for SETI
Standard narrowband searches optimized for razor-thin signals may miss real transmissions from active stellar environments. Search pipelines should be adapted to remain sensitive to moderately broadened signals, particularly when targeting M dwarfs.