Earth Detecting Earth: Human Baselines for Technosignatures

The search for life beyond Earth includes the search for “technosignatures,” or observational signs of technology. In this work, we explore the current technological capabilities of Earth, both in terms of technosignature emission and detection, establishing standards for the Search for Extraterrestrial Intelligence (SETI). We use the concept of the “ichnoscale” to quantify the relative intensity of technosignatures in units of the same technosignature as produced by Earth’s technology (Socas-Navarro et al. 2021). Using this “Earth Detecting Earth” strategy, we quantify over what distance we could, using current or near-future astronomical detection capabilities, detect a variety of manifestations of present-day Earth technology. We consider the following technological categories: radio transmissions (e.g. METI, planetary radar, and human communication leakage), atmospheric pollutants, surface geoengineering, artificial satellites, and optical laser leakage. In summary, we quantify human technology’s astrophysical detectability and extrapolate this to guide expectations in the search for technosignatures on exoplanets.