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Abstract In an attempt to understand the findings presented in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539), we followed their data analysis methodology, omitting the hot and cold‐load calibrations that are an important part of the standard SOFIA GREAT instrument calibration procedure. This process requires scaling of the Venus off‐source spectra by an arbitrary factor, which in turn introduces residuals of the intrinsic receiver bandpass shape as spurious components in the resulting line/continuum spectra. Although these additional artifacts can be reduced via Fourier‐domain spectral filtering, their removal depends on an ill‐constrained interpolation of the Venus continuum across the PH3 spectral line positions, resulting in an unreliable final spectrum. We therefore conclude that the PH3 lines claimed to be detected in the Comment by Greaves et al. (2023, https://doi.org/10.1029/2023GL103539) originate from data/analysis artifacts, and confirm our original result that there is no evidence for phosphine in the SOFIA Venus data.

46P/Wirtanen is a Jupiter-family comet, probably originating from the solar system’s Kuiper Belt, that now resides on a 5.4 yr elliptical orbit. During its 2018 apparition, comet 46P passed unusually close to the Earth (within 0.08 au), presenting an outstanding opportunity for close-up observations of its inner coma. Here we present observations of HCN, H ^13 CN, and HC ^15 N emission from 46P using the Atacama Compact Array. The data were analyzed using the SUBLIME non-LTE radiative transfer code to derive ^12 C/ ^13 C and ^14 N/ ^15 N ratios. The HCN/H ^13 CN ratio is found to be consistent with a lack of significant ^13 C fractionation, whereas the HCN/HC ^15 N ratio of 68 ± 27 (using our most conservative 1 σ uncertainties), indicates a strong enhancement in ^15 N compared with the solar and terrestrial values. The observed ^14 N/ ^15 N ratio is also significantly lower than the values of ∼140 found in previous comets, implying a strong ^15 N enrichment in 46P’s HCN. This indicates that the nitrogen in Jupiter-family comets could reach larger isotopic enrichments than previously thought, with implications for the diversity of ^14 N/ ^15 N ratios imprinted into icy bodies at the birth of the solar system.

Here we present new constraints on Uranus’s and Neptune’s externally sourced stratospheric water abundance using disk-averaged observations of the 557 GHz emission line from Herschel’s Heterodyne Instrument for the Far-Infrared. Derived stratospheric column water abundances are ${0.54}_{-0.06}^{+0.26}$ × 10 ^14 cm ^−2 for Uranus and ${1.9}_{-0.3}^{+0.2}$ ×10 ^14 cm ^−2 for Neptune, consistent with previous determinations using ISO-SWS and Herschel-PACS. For Uranus, excellent observational fits are obtained by scaling photochemical model profiles or with step-type profiles with water vapor limited to ≤0.6 mbar. However, Uranus’s cold stratospheric temperatures imply a ∼0.03 mbar condensation level, which further limits water vapor to pressures ≤0.03 mbar. Neptune’s warmer stratosphere has a deeper ∼1 mbar condensation level, so emission-line pressure broadening can be used to further constrain the water profile. For Neptune, excellent fits are obtained using step-type profiles with cutoffs of ∼0.3–0.6 mbar or by scaling a photochemical model profile. Step-type profiles with cutoffs ≥1.0 mbar or ≤0.1 mbar can be rejected with 4 σ significance. Rescaling photochemical model profiles from Moses & Poppe to match our observed column abundances implies similar external water fluxes for both planets: ${8.3}_{-0.9}^{+4.0}$ × 10 ^4 cm ^−2 s ^−1 for Uranus and ${12.7}_{-2.0}^{+1.3}$ ×10 ^4 cm ^−2 s ^−1 for Neptune. This suggests that Neptune’s ∼4 times greater observed water column abundance is primarily caused by its warmer stratosphere preventing loss by condensation, rather than by a significantly more intense external source. To reconcile these water fluxes with other stratospheric oxygen species (CO and CO _2 ) requires either a significant CO component in interplanetary dust particles (Uranus) or contributions from cometary impacts (Uranus, Neptune).