SETI & Technosignatures

Fully Fluorinated Non-carbon Compounds NF3 And SF6 As Ideal Technosignature Gases

By Keith Cowing
Status Report
August 31, 2023
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Fully Fluorinated Non-carbon Compounds NF3 And SF6 As Ideal Technosignature Gases
Simulated spectra of an exoplanet with transiting an M5V star with an atmosphere abundance of 1 part-per-million of NF3 and SF6. Top panel: the y-axis shows transit depth (ppm), and the x-axis shows wavelength (μm). Te spectra are simulated from 1 to 23 μm, covering the wavelength span of most of JWST’s observation modes. Te yellow, green, and blue regions show the spectral coverage of NIRSpec, and the red region shows coverage of MIRI LRS. Bottom panel: absorption cross sections in cm2 as a function of wavelength for key molecules of interest. For context, the contemporary Earth abundance levels are 3 ppt37 and 11 ppt38 for NF3 and SF6 respectively. — astro-ph.EP

Waste gas products from technological civilizations may accumulate in an exoplanet atmosphere to detectable levels. We propose nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6) as ideal technosignature gases.

Earth life avoids producing or using any N-F or S-F bond-containing molecules and makes no fully fluorinated molecules with any element. NF3 and SF6 may be universal technosignatures owing to their special industrial properties, which unlike biosignature gases, are not species-dependent. Other key relevant qualities of NF3 and SF6 are: their extremely low water solubility, unique spectral features, and long atmospheric lifetimes.

NF3 has no non-human sources and was absent from Earth’s pre-industrial atmosphere. SF6 is released in only tiny amounts from fluorine-containing minerals, and is likely produced in only trivial amounts by volcanic eruptions. We propose a strategy to rule out SF6’s abiotic source by simultaneous observations of SiF4, which is released by volcanoes in an order of magnitude higher abundance than SF6.

Other fully fluorinated human-made molecules are of interest, but their chemical and spectral properties are unavailable. We summarize why life on Earth-and perhaps life elsewhere-avoids using F. We caution, however, that we cannot definitively disentangle an alien biochemistry byproduct from a technosignature gas.

Sara Seager, Janusz J. Petkowski, Jingcheng Huang, Zhuchang Zhan, Sai Ravela, William Bains

Comments: Published as a part of the special collection “Exoplanets” in Scientific Reports
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2308.13667 [astro-ph.EP] (or arXiv:2308.13667v1 [astro-ph.EP] for this version)
Journal reference: Scientific Reports 13.1 (2023): 13576
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Submission history
From: Janusz Petkowski
[v1] Fri, 25 Aug 2023 20:48:15 UTC (3,317 KB)
Astrobiology, Astrochemistry,

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) 🖖🏻