Earth Detecting Earth: At what distance could Earth's constellation of technosignatures be detected with present-day technology?

TL;DR

This paper assesses the maximum detection distances of Earth's technosignatures across various wavelengths using current technology, highlighting the importance of radio signals and the diversity of detectable signs of human activity.

Contribution

It provides a comprehensive, cross-wavelength comparison of Earth's technosignatures detectable with present-day instruments, focusing on Earth-centric signals rather than extraterrestrial ones.

Findings

Radio transmissions, especially planetary radar, are detectable at the greatest distances.

Earth's technosignatures span 13 orders of magnitude in detectability.

Radio frequencies remain the most significant for SETI detection efforts.

Abstract

The field of the Search for Extraterrestrial Intelligence (SETI) searches for ``technosignatures'' that could provide the first detection of life beyond Earth through the technology that an extraterrestrial intelligence (ETI) may have created. Any given SETI survey, if no technosignatures are detected, should set upper limits based on the kinds of technosignatures it should have been able to detect; the sensitivity of many SETI searches requires that their target sources (e.g., Dyson spheres or Kardashev II/III level radio transmitters) emit with power far exceeding the kinds of technology humans have developed. In this paper, we instead turn our gaze Earthward, minimizing the axis of extrapolation by only considering transmission and detection methods commensurate with an Earth-2024 level. We evaluate the maximum distance of detectability for various present-day Earth technosignatures -- radio transmissions, atmospheric technosignatures, optical and infrared signatures, and objects in space or on planetary surfaces -- using only present-day Earth instruments, providing one of the first fully cross-wavelength comparisons of the growing toolbox of SETI techniques. In this framework, we find that Earth's space-detectable signatures span 13 orders of magnitude in detectability, with intermittent, celestially-targeted radio transmission (i.e., planetary radar) beating out its nearest non-radio competitor by a factor of $10^3$ in detection distance. This work highlights the growing range of ways that exoplanet technosignatures may be expressed, the growing complexity and visibility of the human impact upon our planet, and the continued importance of the radio frequencies in SETI.