SETI & Technosignatures

The Detectability Of Nightside City Lights On Exoplanets

By Keith Cowing
May 25, 2021
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The Detectability Of Nightside City Lights On Exoplanets
CIty lights

I estimate the detectability of nightside city lights on habitable, Earth-like, exoplanets around nearby stars using direct-imaging observations from the proposed LUVOIR and HabEx observatory architectures.

I used data from the Soumi National Polar-orbiting Partnership satellite to determine the broadband surface flux from city lights at the top of Earth’s atmosphere, and the spectra of commercially available high-power lamps to model the spectral energy distribution of the emitted flux from city lights. I also consider how the detectability scales with urbanization fraction: from Earth’s value of 0.05%, up to the limiting case of an ecumenopolis — or planet-wide city. I then calculate the minimum detectable urbanization fraction using 100 hours of observing time for generic Earth-analogs around stars with 10 pc of the Sun and for nearby known potentially habitable planets.

Though Earth itself would not be detectable by LUVOIR or HabEx, planets around M-dwarfs close to the Sun would show detectable signals from city lights for urbanization levels of 0.4% to 3%, while the city lights on planets around nearby Sun-like stars would be detectable at urbanization levels of ≳10%. The known planet Proxima b is a particularly compelling target for LUVOIR A observations, which would be able to detect city lights at an urbanization level ten times that of Earth in 100 hours, a level of urbanization that is expected to occur on Earth around the mid-22nd-century. An ecumenopolis, or planet-wide city, would be detectable around roughly 80 nearby stars by both LUVOIR and HabEx, and a survey of all these systems would be able to place a 1σ upper limit of ≲1.4% on the frequency of ecumenopolis planets in the Solar neighborhood assuming no detections.

Thomas G. Beatty

Comments: Submitted to MNRAS. Comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Popular Physics (physics.pop-ph)
Cite as: arXiv:2105.09990 [astro-ph.EP] (or arXiv:2105.09990v1 [astro-ph.EP] for this version)
Submission history
From: Thomas Beatty
[v1] Thu, 20 May 2021 18:45:21 UTC (1,948 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻