Artificial Signals in Transits | Ranger Liu | IAUS404

Transit Information Density: An Artificiality Metric for Transit-Based Technosignatures Presented by Ranger Liu University of Washington Presented at IAU Symposium 404: Advancing the Search for Technosignatures | 2–6 March 2026 ABSTRACT: Humanity's success at discovering and characterizing planets with the transit technique suggests that other civilizations would also recognize this technique as a ubiquitous tool for astronomical exploration. Transit lightcurves may therefore be a potential channel for broadcasting a SETI beacon. We consider a scenario where transit-based technosignatures are created by an artificial occulting object capable of changing its size to encode messages through patterns of regularly-occurring transits at varying depths. We use concepts from information theory to define transit information density (TID), a quantitative metric of artificiality for multi-transit signals. We show that natural periodic patterns and random patterns of transits have distinct characteristic behaviors under TID. We then explore different methods of constructing unambiguously intentional transit-based signals that display non-periodic and non-random behaviors under TID, including heuristic-driven algorithms and encodings of text and mathematical sequences. We also demonstrate a simplified application of TID to complex multi-planet systems like TRAPPIST-1. This technique can be generalized to search for artificial patterns in extant transit surveys such as Kepler. KEYWORDS: transit technosignatures, artificial occultation, information theory, SETI beacon, transit light curves, TRAPPIST-1, Kepler data, exoplanet transits, transit encoding Presented 2–6 March during Advancing the Search for Technosignatures, an online symposium from the International Astronomical Union (IAU; https://www.iau.org/) and Blue Marble Space Institute of Science (BMSIS; https://bmsis.org/).