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We present the results for the detectability of the O₂and O₃molecular species in the atmosphere of an Earth-like planet using reflected light at visible wavelengths. By quantifying the detectability as a function of the signal-to-noise ratio (S/N), we can constrain the best methods to detect these biosignatures with next-generation telescopes designed for high-contrast coronagraphy. Using 25 bandpasses between 0.515 and 1μm and a preconstructed grid of geometric albedo spectra, we examined the spectral sensitivity needed to detect these species for a range of molecular abundances. We first replicate a modern-Earth twin atmosphere to study the detectability of current O₂and O₃levels, and then expand to a wider range of literature-driven abundances for each molecule. We constrain the optimal 20%, 30%, and 40% bandpasses based on the effective S/N of the data, and define the requirements for the possibility of simultaneous molecular detection. We present our findings of O₂and O₃detectability as functions of the S/N, wavelength, and abundance, and discuss how to use these results for optimizing future instrument designs. We find that O₂is detectable between 0.64 and 0.83μm with moderate-S/N data for abundances near that of modern Earth and greater, but undetectable for lower abundances consistent with a Proterozoic Earth. O₃is detectable only at very high S/N data in the case of modern-Earth abundances; however, it is detectable at low-S/N data for higher O₃abundances that can occur from efficient abiotic O₃production mechanisms.

Detecting H₂O in exoplanet atmospheres is the first step on the path to determining planet habitability. Coronagraphic design currently limits the observing strategy used to detect H₂O, requiring the choice of specific bandpasses to optimize abundance constraints. In order to examine the optimal observing strategy for initial characterization of habitable planets using coronagraph-based direct imaging, we quantify the detectability of H₂O as a function of signal-to-noise ratio (S/N) and molecular abundance across 25 bandpasses in the visible wavelength range (0.5–1μm). We use a preconstructed grid consisting of 1.4 million geometric albedo spectra across a range of abundance and pressure, and interpolate to produce forward models for an efficient nested sampling routine, PSGnest. We first test the detectability of H₂O in atmospheres that mimic a modern-Earth twin, and then expand to examine a wider range of H₂O abundances; for each abundance value, we constrain the optimal 20% bandpasses based on the effective S/N of the data. We present our findings of H₂O detectability as functions of S/N, wavelength, and abundance, and discuss how to use these results for optimizing future coronographic instrument design. We find that there are specific points in wavelength where H₂O can be detected down to 0.74μm with moderate-S/N data for abundances at the upper end of Earth’s presumed historical values, while at 0.9μm, detectability is possible with low-S/N data at modern Earth abundances of H₂O.

We analyzed spectral cubes of Callisto’s leading and trailing hemispheres, collected with the NIRSpec Integrated Field Unit (G395H) on the James Webb Space Telescope. These spatially resolved data show strong 4.25μm absorption bands resulting from solid-state¹²CO₂, with the strongest spectral features at low latitudes near the center of its trailing hemisphere, consistent with radiolytic production spurred by magnetospheric plasma interacting with native H₂O mixed with carbonaceous compounds. We detected CO₂rovibrational emission lines between 4.2 and 4.3μm over both hemispheres, confirming the global presence of CO₂gas in Callisto’s tenuous atmosphere. These results represent the first detection of CO₂gas over Callisto’s trailing side. The distribution of CO₂gas is offset from the subsolar region on either hemisphere, suggesting that sputtering, radiolysis, and geologic processes help sustain Callisto’s atmosphere. We detected a 4.38μm absorption band that likely results from solid-state¹³CO₂. A prominent 4.57μm absorption band that might result from CN-bearing organics is present and significantly stronger on Callisto’s leading hemisphere, unlike¹²CO₂, suggesting these two spectral features are spatially antiassociated. The distribution of the 4.57μm band is more consistent with a native origin and/or accumulation of dust from Jupiter’s irregular satellites. Other, more subtle absorption features could result from CH-bearing organics, CO, carbonyl sulfide, and Na-bearing minerals. These results highlight the need for preparatory laboratory work and improved surface–atmosphere interaction models to better understand carbon chemistry on the icy Galilean moons before the arrival of NASA’s Europa Clipper and ESA’s JUICE spacecraft.

High-resolution near-infrared ground-based spectroscopic observations of comet 67P/Churyumov–Gerasimenko near its maximum activity in 2021 were conducted from the W. M. Keck Observatory, using the facility spectrograph NIRSPEC. 67P is the best-studied comet to date because of the unprecedented detail and insights provided by the Rosetta mission during 2014–2016. Because 67P is the only comet where the detailed abundances of many coma volatiles were measured in situ, determining its composition from the ground provides a unique opportunity to interpret Rosetta results within the context of the large database of ground-based compositional measurements of comets. However, previous apparitions, including in 2015, have been unfavorable for in-depth ground-based studies of parent volatiles in 67P. The 2021 apparition of 67P was thus the first-ever opportunity for such observations. We report gas spatial distributions, rotational temperatures, production rates, and relative abundances (or stringent upper limits) among seven volatile species: C₂H₂, C₂H₆, HCN, NH₃, CH₃OH, H₂CO, and H₂O. The measured abundances of trace species relative to water reveal near average or below average values compared to previous comets studied at infrared wavelengths. Both gas rotational temperatures and the spatial distributions of H₂O, C₂H₆, and HCN measured with Keck-NIRSPEC in 2021 are consistent with the outgassing patterns revealed by Rosetta in 2015 at very similar heliocentric distance  (post-perihelion). These results can be integrated with both Rosetta mission findings and ground-based cometary studies of the overall comet population, for which we encourage a wide-scale collaboration across measurement techniques.