The Futility of Exoplanet Biosignatures


Different underlying planetary processes can lead to the same atmospheric observables, which means that a specific observation of an atmosphere cannot unambiguously identify the surface processes, including biological ones. Uncertainty in the types and scale of novel chemistry, planetary processes, and biotic processes amplify this problem.

The ultimate goal of astrobiology is to determine the distribution and diversity of life in the universe. But as the word "biosignature" suggests, what will be detected is not life itself, but an observation implicating a particular process associated with living systems.

Technical constraints and our limited access to other worlds suggest we are more likely to detect an out-of-equilibrium suite of gasses than a writhing octopus. Yet, anything short of a writhing octopus will raise skepticism among astrobiologists about what has been detected. Resolving that skepticism requires a theory to delineate processes due to life and those due solely to abiotic mechanisms.

This poses an existential question for the endeavor of life detection: How do astrobiologists plan to detect life via features shared between non-living and living systems? We argue that you cannot without an underlying theory of life. We illustrate this by analyzing the hypothetical detection of an "Earth 2.0" exoplanet. In the absence of a theory of life, we argue the community should focus on identifying unambiguous features of life via four areas of active research: understanding the principles of life on Earth, building life in the lab, detecting life in the solar system and searching for technosignatures. Ultimately, we ask, what exactly do astrobiologists hope to learn by searching for life?

Harrison B. Smith, Cole Mathis

Comments: 15 pages, 2 figures, 1 box
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Other Quantitative Biology (q-bio.OT)
Cite as: arXiv:2205.07921 [astro-ph.EP] (or arXiv:2205.07921v1 [astro-ph.EP] for this version)

https://doi.org/10.48550/arXiv.2205.07921
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Submission history
From: Harrison Smith [view email]
[v1] Mon, 16 May 2022 18:11:44 UTC (926 KB)
https://arxiv.org/abs/2205.07921
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