Undetected past contacts with technological species: implications for technosignature science

Abstract

In the search for extraterrestrial intelligence (SETI), the highly incomplete sampling of the technosignature search space is often considered as a plausible explanation for the persistent lack of detections over six decades of searches. If correct, this would imply that technosignatures may already have reached Earth without being detected or correctly identified. Here, we explore this possibility using a Bayesian inference framework to estimate present-day detectability given $n\ge 1$ undetected contacts over the past 65 years -- the period since the first SETI experiment. We show that achieving high detectability of technosignatures emitted within a few hundred light-years of Earth would require implausibly large $n$ values, even exceeding the population of habitable planets within that range. More conservative estimates can be obtained only assuming that emitters are tightly clustered near Earth or that their population in the Milky Way has undergone a very recent and sudden boost. This tension is further exacerbated for short-lived technosignatures and persists whether they are omnidirectional, as in Dysonian megastructures, or directional, as in intentional communication attempts. These findings suggest that, if undetected past contacts from the Milky Way have indeed occurred, the best prospects of detection may lie in searches extending over several thousand light-years, though only a few detectable technoemissions would be expected.

arXiv comment11 pages, 4 figures

References in corpus (31)

• The mass distribution and gravitational potential of the Milky Way
• The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data
• The Breakthrough Listen Search for Intelligent Life: 1.1-1.9 GHz observations of 692 Nearby Stars
• Bayesian analysis of the astrobiological implications of life's early emergence on Earth
• The Breakthrough Listen Search for Intelligent Life: Observations of 1327 Nearby Stars over 1.10-3.45 GHz
• The Temporal Aspect of the Drake Equation and SETI
• How Much SETI Has Been Done? Finding Needles in the n-Dimensional Cosmic Haystack
• Detecting industrial pollution in the atmospheres of earth-like exoplanets
• Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology
• Fast Radio Bursts from Extragalactic Light Sails
• Natural and Artificial Spectral Edges in Exoplanets
• Extending the Breakthrough Listen nearby star survey to other stellar objects in the field
• The Fermi Paradox and the Aurora Effect: Exo-civilization Settlement, Expansion and Steady States
• Detectability of Chlorofluorocarbons in the Atmospheres of Habitable M-dwarf Planets
• Sizing Up the Milky Way: A Bayesian Mixture Model Meta-Analysis of Photometric Scale Length Measurements
• Searching for broadband pulsed beacons from 1883 stars using neural networks
• Bayesian approach to SETI
• Project Hephaistos I. Upper limits on partial Dyson spheres in the Milky Way
• Signal coverage approach to the detection probability of hypothetical extraterrestrial emitters in the Milky Way
• Longevity is the key factor in the search for technosignatures
• Multibeam Blind Search of Targeted SETI Observations toward 33 Exoplanet Systems with FAST
• The Impact of the Temporal Distribution of Communicating Civilizations on their Detectability
• Power Beaming Leakage Radiation as a SETI Observable
• Prospects for Detecting Signs of Life on Exoplanets in the JWST Era
• A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15-1.73 GHz
• Upper limits on transmitter rate of extragalactic civilizations placed by Breakthrough Listen observations
• COSMIC's Large-Scale Search for Technosignatures during the VLA sky Survey: Survey Description and First Results
• A Search for Monochromatic Light Toward the Galactic Centre
• Panoramic SETI: Program Update and High-Energy Astrophysics Applications
• Inferring the rate of technosignatures from 60 yr of nondetection
• An Extragalactic Widefield Search for Technosignatures with the Murchison Widefield Array