The Effect Of Spectral Resolution On Biosignature Detection Via Reflected Light Observations Of The Earth Through Time

NASA’s Habitable Worlds Observatory (HWO) will search for biosignatures on Earth-like exoplanets using reflected light spectroscopy.

A critical instrument design parameter is resolving power, which must balance biosignature detectability against exposure time and detector noise constraints. We assess the resolving power needed to detect and characterize key biosignature gases and habitability indicators including O₂, O₃, H₂O, CH₄, CO₂ and CO across atmospheres representing the Archean, Proterozoic, and Phanerozoic Earth.

We combine analytical detectability calculations spanning spectral resolutions (λ/Δλ) R=20-5000 with atmospheric retrievals using the r_fast radiative transfer model and pyEDITH exposure time calculator for realistic wavelength-dependent noise modeling.

In the visible (0.4-1.0 μm), the nominal resolution R_Vis=140 is sufficient for detecting O₂ in Phanerozoic-like atmospheres. Higher resolutions could theoretically reduce exposure times for low-O₂ Proterozoic atmospheres, but require >10× reductions in dark current and could increase H₂O detection exposure times by ∼2×, penalizing the foundational habitability constraint that anchors downstream biosignature searches.

The most efficient path for low-O₂ atmospheres may instead be indirect inference via O₃, whose Hartley-Huggins bands are detectable at R_UV∼7. In the near-IR (1.0-1.7 μm), R_NIR≥40 is necessary to avoid a degeneracy between CO₂ and CO that could produce false positive detections of abundant CO. The nominal R_NIR=70 is sufficient for characterizing all Earth-through-time cases.

These results support HWO’s current baseline resolution choices and provide actionable guidance for finalizing spectrometer requirements while maintaining technological feasibility for the search for life on exoplanets.

Samantha Gilbert-Janizek, Jacob Lustig-Yaeger, Joshua Krissansen-Totton

Comments: Accepted at The Astrophysical Journal; 27 pages, 11 figures, 5 tables, 1 appendix
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2604.26925 [astro-ph.EP] (or arXiv:2604.26925v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2604.26925
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Submission history
From: Samantha Gilbert-Janizek
[v1] Wed, 29 Apr 2026 17:39:38 UTC (11,499 KB)
https://arxiv.org/abs/2604.26925

Astrobiology, exoplanet,