Exo-IPM Distortions in Narrowband Signals: A Framework for Spectral Broadening and Scintillation in Solar and Exoplanetary Environments

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Grayce Brown and Vishal Gajjar explain that narrowband radio signals in space are broadened and flicker by plasma irregularities in the solar wind, and they develop a framework to quantify how spectral broadening relates inversely to the scintillation timescale across turbulence models, orbital orientations, and stellar types, anchor it with real solar-system spacecraft data to map how broadening varies with distance and helio-latitude, then apply the idea to hypothetical alien signals around Sun-like stars and other stars with particular focus on M dwarfs where activity and mass loss are higher, all to improve technosignature searches and refine limits on interstellar communication by accounting for Exo-IPM distortions, a result presented at the 246th AAS meeting in June 2025.

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Impact of Stellar Wind on Narrowband Technosignatures

Narrowband signals from spacecraft in the Solar System experience spectral broadening and intensity scintillations due to plasma density irregularities in the solar wind. With the current capabilities of radio telescopes, these distortions complicate the identification of such signals. It is logical, then, that ETI signals would also experience spectral broadening and scintillation from turbulence in the interplanetary medium of their own exoplanetary systems (Exo-IPMs). To aid the search of radio technosignatures, we develop a theoretical framework to quantify the limits of spectral broadening, which is inversely proportional to the scintillation timescale, across various turbulence models, orbital orientations, and stellar spectral types. We first examine the effects of the solar wind on real narrowband signals from spacecraft in the solar system and develop an empirical model of the radial and helio-latitudinal dependence of spectral broadening. We then model hypothetical situations of narrowband ETI signals originating from planets of different orbital orientations around Sun-like stars, before extrapolating the solar model to stars of other spectral types with a focus on M dwarfs. We expect broadening from M dwarf systems to be enhanced due to increased stellar activity and mass loss compared to the Sun. Here we present the results of such a theoretical investigation of this overlooked aspect of Exo-IPM impact on technosignature searches. Our findings have broad implications for optimizing radio technosignature searches and refining constraints on interstellar communication.