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Wavelength Requirements for Life Detection via Reflected Light Spectroscopy of Rocky Exoplanets
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Wavelength Requirements for Life Detection via Reflected Light Spectroscopy of Rocky Exoplanets
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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 $\mu$m) and extending into the near infrared (1.7 $\mu$m), is necessary for contextualizing biosignatures with HWO. The short wavelength cutoff is driven by the need to identify Proterozoic-like biospheres via O$_3$, whereas the long wavelength cutoff is driven by the need to contextualize O$_2$ and CH$_4$ 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 $\mu$m 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..
Forward citations
Cited by 12 Pith papers
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Splitting biosignature survey targets into two groups with different life prevalences but a shared global confounder rate allows modest-sized surveys to produce strong evidence for life under fully agnostic priors.
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Residual habitable-zone dust adds continuum light that can cut apparent molecular band depths by up to 50%, forcing exozodi residual to below 0.1% of planet flux for abundance retrievals.
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The Rocky Planet Picture Show: Implementation of Surface Reflection and Emission in $\texttt{POSEIDON}$ with Application to and Interpretation of JWST Data
POSEIDON now includes lab-derived rocky surface albedos, enabling JWST emission spectra to separate thin versus thick atmospheres and potentially identify granite-like versus basaltic surfaces.
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Toward Inferring the Surface Fluxes of Biosignature Gases on Rocky Exoplanets from Telescope Spectra
A retrieval technique infers surface gas fluxes from exoplanet spectra via inversion of a photochemical-climate model, demonstrated on synthetic TRAPPIST-1 e data with an Archean-like biosphere.
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The First Remotely Detected Biosignature May Not Be the Most Common: Implications for JWST and HWO
Selection effects in JWST transmission spectroscopy and HWO reflected-light imaging may cause the first biosignature detection to arise from an atypical planet rather than a representative Earth analog.
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Impact of Climate States and Seasons on Future Exo-Earth Observations
Climate states on exoplanets with the same atmospheric composition create different reflectance spectra, changing the detectability of atmospheric features and biosignatures, with seasonal variations on high-obliquity...
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Design and development of a near-IR integral field spectrograph for the HWO Coronagraph Instrument
Early design trades for an HWO near-IR IFS favor a lenslet architecture and identify sampling, anamorphic packing, and crosstalk controls as the main levers on exoplanet yield.
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Near UV Stellar Activity and Brightness Fluctuations of the Alpha Centauri AB Star System from Weeks to Decades -- Inputs for Reflected Light Spectroscopy with HWO
Alpha Centauri A shows low NUV variability with rare flares, while B shows higher variability tied to its 8-year cycle, informing exoplanet reflected light spectroscopy.
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The effect of spectral resolution on biosignature detection via reflected light observations of the Earth through time
Nominal HWO resolutions suffice to detect key biosignatures across Archean to Phanerozoic Earth atmospheres, with O3 enabling indirect low-O2 detection and NIR resolution preventing CO2-CO false positives.
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Design and development of a near-IR integral field spectrograph for the HWO Coronagraph Instrument
Design study comparing lenslet and image-slicer architectures for a 0.8-1.7 μm IFS for the HWO coronagraph, with requirements for speckle sampling, throughput, and crosstalk control, plus identification of needed tech...
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Detecting habitable exoplanet atmospheres with LIFE, the Large Interferometer for Exoplanets
A mission pitch, not a discovery paper: LIFE's claimed superiority over HWO for detecting the O3+CH4 biosignature pair restates the LIFE collaboration's own published simulations, with a UK funding proposal added.
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