Wavelength Requirements For Life Detection Via Reflected Light Spectroscopy Of Rocky Exoplanets

Searching for signs of life is a primary goal of the Habitable Worlds Observatory (HWO). However, merely detecting oxygen, methane, or other widely discussed biosignatures is insufficient evidence for a biosphere.

In parallel with biosignature detection, exoplanet life detection additionally requires characterization of the broader physicochemical context to evaluate planetary habitability and the plausibility that life could produce a particular biosignature in a given environment.

Life detection further requires that we can confidently rule out photochemical or geological phenomena that can mimic life (i.e. “false positives”). Evaluating false positive scenarios may require different observatory specifications than biosignature detection surveys.

Here, we explore the coronagraph requirements for assessing habitability and ruling out known false positive (and false negative) scenarios for oxygen and methane, the two most widely discussed biosignatures for Earth-like exoplanets.

We find that broad wavelength coverage ranging from the near UV (0.26 μm) and extending into the near infrared (1.7 μm), is necessary for contextualizing biosignatures with HWO. The short wavelength cutoff is driven by the need to identify Proterozoic-like biospheres via O₃, whereas the long wavelength cutoff is driven by the need to contextualize O₂ and CH₄ biosignatures via constraints on C-bearing atmospheric species.

The ability to obtain spectra with signal-to-noise ratios of 20-40 across this 0.26-1.7 μm range (assuming R=7 UV, R=140 VIS, and R=70 NIR) is also required. Without sufficiently broad wavelength coverage, we risk being unprepared to interpret biosignature detections and may ultimately be ill-equipped to confirm the detection of an Earth-like biosphere, which is a driving motivation of HWO.

Known biosignature false positive scenarios and their contextual clues for rocky planets
around F/G/K stars. Only bolded scenarios with shaded backgrounds are considered in this study. — astro-ph.EP

Joshua Krissansen-Totton, Anna Grace Ulses, Maxwell Frissell, Samantha Gilbert-Janizek, Amber Young, Jacob Lustig-Yaeger, Tyler Robinson, Stephanie Olson, Eleonora Alei, Giada Arney, Celeste Hagee, Chester Harman, Natalie Hinkel, Emilie Lafleche, Natasha Latouf, Avi Mandell, Mark M. Moussa, Niki Parenteau, Sukrit Ranjan, Blair Russell, Edward W. Schwieterman, Clara Sousa-Silva, Armen Tokadjian, Nicholas Wogan

Comments: In review at Astrobiology. Comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.14771 [astro-ph.EP] (or arXiv:2507.14771v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2507.14771
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Submission history
From: Joshua Krissansen-Totton
[v1] Sat, 19 Jul 2025 23:58:29 UTC (2,000 KB)
https://arxiv.org/abs/2507.14771
Astrobiology, Astronomy,