[Paper Review] Life Beyond the Solar System: Remotely Detectable Biosignatures

Shawn Domagal‐Goldman, Nancy Y. Kiang+39 more|arXiv (Cornell University)|Jan 20, 2018

Astro and Planetary Science7 references3 citations

TL;DR

This white paper synthesizes the consensus of the Exoplanet Biosignatures Workshop Without Walls on detecting life beyond Earth using remote sensing of exoplanet atmospheres and surfaces. It advocates for a multidisciplinary, Bayesian framework integrating biology, planetary science, and astrophysics to identify robust biosignatures, assess false positives, and guide future telescopes like James Webb and LUVOIR.

ABSTRACT

For the first time in human history, we will soon be able to apply the scientific method to the question "Are We Alone?" The rapid advance of exoplanet discovery, planetary systems science, and telescope technology will soon allow scientists to search for life beyond our Solar System through direct observation of extrasolar planets. This endeavor will occur alongside searches for habitable environments and signs of life within our Solar System. While the searches are thematically related and will inform each other, they will require separate observational techniques. The search for life on exoplanets holds potential through the great diversity of worlds to be explored beyond our Solar System. However, there are also unique challenges related to the relatively limited data this search will obtain on any individual world. This white paper reviews the scientific community's ability to use data from future telescopes to search for life on exoplanets. This material summarizes products from the Exoplanet Biosignatures Workshop Without Walls (EBWWW). The EBWWW was constituted by a series of online and in person activities, with participation from the international exoplanet and astrobiology communities, to assess state of the science and future research needs for the remote detection of life on planets outside our Solar System.

Motivation & Objective

• To establish a community-wide scientific consensus on the current state and future research priorities for remotely detecting life on exoplanets.
• To address the challenge of interpreting limited spectral data from distant exoplanets with high confidence in biosignature detection.
• To integrate biological, planetary, and astrophysical knowledge into a unified framework for assessing planetary habitability and life.
• To identify critical research gaps in modeling abiotic processes, biosignature expression under diverse stellar environments, and uncertainty quantification.
• To advocate for institutional and public-private partnerships to develop advanced computational tools and models for biosignature detection.

Proposed method

• Synthesizing findings from five peer-reviewed manuscripts produced by the Exoplanet Biosignatures Workshop Without Walls, covering biosignature libraries, O₂ as a case study, statistical frameworks, and future observatory capabilities.
• Applying a Bayesian statistical framework to integrate diverse scientific disciplines and quantify confidence in biosignature detections.
• Using 1D and 3D planetary system models (including GCMs) to simulate biosignature expression under varying stellar inputs, atmospheric compositions, and planetary conditions.
• Evaluating the detectability of biosignatures through modeling spectral features of gases (e.g., O₂, CH₄, O₃) and surface reflectance under different planetary and stellar environments.
• Incorporating prior probabilities of life based on planetary context, including climate, geology, and stellar type, to reduce false positive risks.
• Advocating for collaborative development of open-source scientific software with professional programmers to model biosignature systems and uncertainty propagation.

Experimental results

Research questions

• RQ1 What are the most reliable remotely detectable biosignatures for exoplanets, and how can we distinguish them from abiotic false positives?
• RQ2 How do planetary and stellar environments—especially different host stars—affect the expression and detectability of biosignatures like O₂ and O₃?
• RQ3 What role does a planet’s geological and atmospheric context play in assessing the likelihood of life, and how can this be quantified?
• RQ4 How can a Bayesian framework be used to integrate biological, atmospheric, and astrophysical data to improve confidence in biosignature detection?
• RQ5 What future space and ground-based telescopes are required to achieve high-contrast, high-resolution spectroscopy of Earth-like exoplanets in habitable zones?

Key findings

• The scientific community has reached a consensus that O₂ is a strong but context-dependent biosignature, requiring careful evaluation of abiotic production pathways to avoid false positives.
• A Bayesian framework is essential for integrating diverse data types and modeling uncertainties, enabling probabilistic assessments of life beyond Earth.
• Future missions such as James Webb Space Telescope (JWST), LUVOIR, HabEx, and the ground-based ELT, GMT, and TMT are critical for detecting biosignatures on Earth-like exoplanets.
• 3D general circulation models (GCMs) and coupled 1D models of planetary systems are necessary to simulate biosignature expression across atmospheric, oceanic, and surface processes.
• Significant research gaps remain in modeling non-Earth-like biosignatures and abiotic processes under extreme or exotic planetary conditions.
• Public-private partnerships are essential to develop advanced computational tools and scientific software for biosignature modeling and uncertainty quantification.