Prof. Patrick Irwin

Abstract:

Over four decades have elapsed since the last in situ spectrophotometric observations of the Venusian atmosphere, specifically from the Venera 11 (1978) and Venera 13 and 14 (1982) missions. These missions recorded spectral data during their descent from approximately 62 km to the surface. Unfortunately, the original data were lost; however, a portion has been reconstructed by digitising the graphical outputs that were generated during the initial data processing phase of each of the three missions [1]. This reconstructed data is crucial as it remains the sole set of in situ spectrophotometric observations of Venus’s atmosphere and is likely to be so for the foreseeable future.While re-analysing the reconstructed Venera datasets, we identified several artefacts, errors and sources of noise, necessitating the implementation of some corrections and validation checks to isolate the most unaffected part of the reconstructed data. Then, using NEMESIS, a radiative transfer and retrieval tool [2], we conducted a series of retrievals to simultaneously fit the downward-going spectra at all altitudes. During this process, several parameters were retrieved. The first set of retrievals focused on the structure of the main cloud deck (MCD), which includes the cloud base altitude and abundance profiles of all four cloud modes. Previous corrections that were used to account for the effect of the unknown UV absorber did not result in good fits with the spectra shortward of 0.6 µm. Hence, we derived a new correction by retrieving the imaginary refractive index spectra of the Mode 1 particles.In the next phase, the MCD retrievals were used to update the model atmospheres for each of the missions. Then, the H2O volume mixing ratio profiles were retrieved and compared with the previous retrievals using the same data by [1] along with other remote sensing observations. The final retrieval phase concentrated on characterising particulate matter in the deep atmosphere. In [3], we outlined a methodology for retrieving a near-surface particulate layer using the reconstructed Venera 13 dataset. In this new work, we apply this methodology to encompass the Venera 11 and 14 datasets and compare the retrievals from the three datasets.This research thus provides a comprehensive overview of three distinct retrievals: 1) main cloud deck, 2) H2O, and 3) near-surface particulates using the reconstructed spectrophotometric data of Venera 11, 13, and 14.References: [1] Ignatiev, N. I., Moroz, V. I., Moshkin, B. E., Ekonomov, A. P., Gnedykh, V. I., Grigor’ev, A. V., and Khatuntsev, I. V. Cosmic Research 35(1), 1–14 (1997).[2] Irwin, P. G., Teanby, N. A., de Kok, R., Fletcher, L. N., Howett, C. J., Tsang, C. C., Wilson, C. F., Calcutt, S. B., Nixon, C. A., and Parrish, P. D. Journal of Quantitative Spectroscopy and Radiative Transfer 109(6), 1136–1150 (2008).[3] Kulkarni, S. V., Irwin, P. G. J., Wilson, C. F., & Ignatiev, N. I. Journal of Geophysical Research: Planets, 130, e2024JE008728, (2025).

Abstract:

We present a re-analysis of archival data-cubes of Neptune obtained with the GEMINI Near-Infrared Integral Field Spectrometer (NIFS), aiming to refine constraints on the abundance of hydrogen sulphide (H₂S) in Neptune's atmosphere. To enhance spatial and spectral fidelity, we employ a modified CLEAN algorithm that effectively deconvolves the data while conserving flux. To mitigate observational and instrumental artifacts, we utilize Singular Spectrum Analysis (SSA) on single-wavelength images and apply Principal Component Analysis (PCA) across the full data-cube to suppress both random and systematic noise. Spectral retrievals are conducted using ArchNemesis, an optimal estimation inverse modeling tool. We retrieve vertical profiles at individual locations, and use Minnaert-corrected reflectivity functions across latitude bands to investigate latitudinal variability. Using the deconvolution and data analysis techniques, we are able to extract more scientific utility from legacy datasets and describe a template that can be repeated for similar datasets.

Abstract:

Titan’s substantial atmosphere is primarily composed of molecular nitrogen (N2) and methane (CH4), which are dissociated by solar UV photons and subsequently generate a vast chemical network of trace gases. The composition of Titan’s atmosphere is markedly different than that of Saturn, including both the complex molecular inventory and the hitherto measured isotopic ratios – including that of nitrogen (14N/15N). Atmospheric and interior evolution models (e.g., Mandt et al., 2014) indicate that the atmospheres of Saturn and Titan did not form in the same manner or from the same constituents, and that Titan’s atmospheric N2 may have originated from its interior as NH3. The evolution of 14N/15N in Titan’s atmosphere over time does not result in a value comparable to that measured on Saturn and instead is closer to cometary values; this indicates that the origin of Titan’s atmosphere appears to be from protosolar planetesimals enriched in ammonia and not from the sub-Saturnian nebula. However, selective isotopic fractionation of molecular species in Titan’s atmosphere complicates this picture, as the isotopic ratios may vary as a function of altitude (Figure 1). To further constrain the evolution of Titan’s atmosphere – and indeed, its origin – isotopic ratios must be measured throughout its atmosphere, instead of being interpreted from bulk values likely only representative of the stratosphere.While the measurement of Titan’s 14N/15N in N2 (167.7; Niemann et al. 2010) places it firmly below the lower limit derived for Saturn (~350; Fletcher et al., 2014), Titan’s atmospheric nitriles (e.g., HCN, HC3N, CH3CN) are further enriched in 15N, resulting in ratios closer to 70 (Molter et al., 2016; Cordiner et al., 2018; Nosowitz et al., 2025). The variation in nitrogen isotopic ratios between the nitriles and N2 is thought to be the result of higher photolytic efficiency of 15N14N compared to N2 in the upper atmosphere (~900 km), resulting in increased 15N incorporated into nitrogen-bearing species (Liang et al., 2007; Dobrijevic & Loison, 2018; Vuitton et al., 2019). As these species are advected to lower altitudes, the nitrogen isotope ratio may vary vertically (Figure 1, red and black profiles), but previous measurements have only presented bulk atmospheric isotope ratios primarily representing Titan’s stratosphere (Figure 1, blue lines).Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have allowed for the derivation of vertical abundance profiles of Titan’s trace atmospheric species and measurements of N, D, and O-bearing isotopologues (Molter et al., 2016; Serigano et al., 2016; Cordiner et al., 2018; Thelen et al., 2019; Nosowitz et al., 2025). However, vertical isotopic ratio profiles have yet to be derived. Here, we utilize observations acquired with ALMA in July 2022 containing high sensitivity measurements of the HC15N J=4–3 transition at 344.2 GHz (~ 0.87 mm) to investigate vertical variations in the 14N/15N of Titan’s HCN. We compare the results of the vertical 14N/15N profile to those predicted by photochemical models to determine the impact of the isotopic-selective photodissociation of nitrogen-bearing molecular species in Titan’s atmosphere, and the impact of the Saturnian and space environments that vary between model implementations.Figure 1. 14N/15N profile for HCN predicted by photochemical models from Vuitton et al. (2019; black line) and Dobrijevic & Loison (2018; red line). Blue colored bars in the lower atmosphere represent previous HCN nitrogen isotope ratios from Cassini, Herschel, and ground-based (sub)millimeter observations (see Molter et al., 2016, and references therein). Measurements are offset vertically for clarity, and all refer to HC14N/HC15N measurements for the bulk stratosphere.References:Cordiner et al., 2018, The Astrophysical Journal Letters, 859, L15.Dobrijevic & Loison, 2018, Icarus, 307, 371.Fletcher et al., 2014, Icarus, 238, 170.Liang et al., 2007, The Astrophysical Journal Letters, 644, L115.Mandt et al. 2014, The Astrophysical Journal Letters, 788, L24.Molter et al., 2016, The Astronomical Journal, 152, 42.Niemann et al., 2010, Journal of Geophysical Research, 115, E12006.Nosowitz et al., 2025, The Planetary Science Journal, 6, 107.Serigano et al., 2016, The Astrophysical Journal Letters, 821, L8.Thelen et al., 2019, The Astronomical Journal, 157, 219.Vuitton et al., 2019, Icarus, 324, 120.

Abstract:

The nature of the red colouration of Jupiter’s belts and some of its major anticyclones is still debated to this day. Sromovsky et al. (2017) proposed the existence of an “universal chromophore” by fitting Cassini/VIMS-V observations. Baines et al. (2019) concluded that this chromophore should be located in a thin layer above the ammonia clouds, giving rise to the so called “Crème Brûlée” model. Both of these works had as a basis the red compound that formed through the reaction of photolyzed ammonia with acetylene as obtained in the laboratory by Carlson et al. (2016).However,  both Pérez-Hoyos et al. (2020) and Braude et al. (2020) found that a less blue and more vertically extended chromophore layer would fit better their HST/ WFC3 North Temperate Belt disturbance observations for the former and latitudinal swath from MUSE/VLT observations for the later, without fully discarding the possible existence of an “universal chromophore”. Recently, analysis of HST/WFC3 images of Jupiter’s Great Red Spot, its surroundings, and, Oval BA by Anguiano-Arteaga et al. (2021,2023) suggest the presence of two distinct colouring aerosols. The first being similar to the “universal chromophore” and the second one being a new UV-absorbing species below the main chromophore layer at tropospheric levels. This highlights the uncertainties on the vertical distribution of aerosols, their properties and their variability.To address this uncertainty, we used new Jupiter spectra obtained with CARMENES (The Calar Alto High-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs) in 2019. This instrument consists of two separated spectrographs with spectral resolutions R = 80,000-100,000, covering the wavelength ranges of 0.52 to 0.96 μm and of 0.96 to 1.71 μm. The original purpose of these observations was to measure winds through the Doppler velocimetry method. We used a downgraded resolution version (R = 173-570) so the observations match the available spectral data for methane, as this resolution is enough for constraining aerosol properties. Due to the original nature of the observations, no calibration star was recorded. In order to achieve flux calibration, we used  2017 observations of Saturn with CARMENES. We employed Saturn’s B ring to obtain the response function of the instrument, since no other sources of calibration are available at the desired resolution or epoch.We used the reflectivity (I/F) spectrum obtained with Cassini/VIMS (Cuzzi et al., 2009) at phase angles less than 3º. We applied the response function to the centre of disc spectrum of Saturn and compared the obtained reflectivity spectrum with results from Clark and McCord (1979) and Mendikoa, et al. (2017). Lastly, we applied the flux calibration to the Jupiter observations and compared them results from Mendikoa, et al., (2017) and Irwin et al. (2018) (Figure 1). All calibrations agree within 10% with MUSE calibration.We were able to perform a Minnaert Limb-darkening approximation and produce 2 synthetic spectra (zenith angle = 0º/61.45º) for five distinct sample areas (EZ (Figure 2), SEB, NEB, transition region from EZ to SEB, and from NEB to NTrZ). We performed retrievals using the same a priori atmospheric parameterization as presented in Braude et al. (2020), Pérez-Hoyos et al. (2020) and Anguiano-Arteaga et al. (2021), comparing the retrieved results of each in order to constrain the uncertainties in the Jovian aerosol scheme. To achieve this, we used the NEMESIS (Nonlinear Optimal Estimator for MultivariatE Spectral analySIS) radiative transfer suite (Irwin et al., 2008). We present here the results of this analysis.Figure 1: Comparison of centre of disk Jupiter spectrum after flux calibration with EZ spectrum from Irwin et al. (2018) and 0º latitude spectrum from Mendikoa et al. (2017).Figure 2: Observation spectra compared to the obtained synthetic spectra after retrieving the atmospheric parameters for the EZ using Braude et al. (2020) model. Top row corresponds to nadir (incidence and emission angle = 0º) and bottom row to limb (incidence and emission angle = 61.45º). Figure 3: Comparison between the a priori aerosol vertical profiles and the retrieved profiles for every region for the model from Braude et al. (2020).  References:Carlson, R. W., et al. (2016). Chromophores from photolyzed ammonia reacting with acetylene: Application to Jupiter's Great Red Spot. Icarus, 274, 106–115. Sromovsky, L. A., et al. (2017). A possibly universal red chromophore for modeling color variations on Jupiter. Icarus, 291, 232–244. Baines, K. H., et al. (2019). The visual spectrum of Jupiter's Great Red Spot accurately modelled with aerosols produced by photolyzed ammonia reacting with acetylene. Icarus, 330, 217–229. Pérez-Hoyos, S., et al. (2020). Color and aerosol changes in Jupiter after a North temperate belt disturbance. Icarus, 132, 114021. Braude, A. S., et al. (2020). Colour and tropospheric cloud structure of Jupiter from MUSE/VLT: Retrieving a universal chromophore. Icarus, 338, 113589. Anguiano-Arteaga, A., et al. (2021). Vertical Distribution of Aerosols and Hazes Over Jupiter's Great Red Spot and Its Surroundings in 2016 From HST/WFC3 Imaging. Journal of Geophysical Research: Planets, 126, e2021JE006996. Anguiano-Arteaga, A., et al. (2023). Temporal variations in vertical cloud structure of Jupiter's Great Red Spot, its surroundings and Oval BA from HST/WFC3 imaging. Journal of Geophysical Research: Planets, 128, e2022JE007427. Karkoschka, E. (1994). Spectrophotometry of the Jovian Planets and Titan at 300- to 1000-nm Wavelength: The Methane Spectrum. Icarus, 111, 1, 174–192. Irwin, P., et al. (2008). The NEMESIS planetary atmosphere radiative transfer and retrieval tool. J. Quant. Spectrosc. Radiat. Transf., 109, 1136–1150. Rodgers CD. (2000). Inverse methods for atmospheric sounding: theory and practice. Singapore: World Scientific. Cuzzi, J., et al., 2009. Ring Particle Composition and Size Distribution. Springer Netherlands, Dordrecht. pp. 459–509. Clark, R.N., McCord, T.B., 1979. Jupiter and Saturn: Near-infrared spectral albedos. Icarus 40, 180–188. Mendikoa, I., et al., 2017. Temporal and spatial variations of the absolute reflectivity of Jupiter and Saturn from 0.38 to 1.7 𝜇m with planetcam-upv/ehu. A&A 607, A72. Irwin, P.G., et al., 2018. Analysis of gaseous ammonia (NH3) absorption in the visible spectrum of Jupiter. Icarus 302, 426–436

Abstract:

Jupiter has the strongest planetary magnetic field and the most volcanically active moon (Io) in the solar system.  Magnetospheric dynamics and interactions with the solar wind ultimately drive ions and electrons deep into its neutral atmosphere producing auroral emissions over a large range of the electromagnetic spectrum.  Energy is deposited as deep as the lower stratosphere, which drives atmospheric heating, dynamics and unique chemistry.  Jupiter provides a natural laboratory to study how the external space environment can modulate a planet’s atmosphere and context for the extreme space weather likely experienced by exoplanets orbiting close to their host star.  In this work, we present an analysis of high-resolution mid-infrared spectra recorded in March 2025 by the TEXES (Texas Echelon Cross Echelle Spectrograph, Lacy et al. 2002, PASP 114, 153) instrument on NASA’s IRTF (Infrared Telescope Facility).  As part of a long-term program, spectral scans were performed across high-northern and high-southern latitudes in settings centered at 8.0, 10.53, 12.21 and 13.70 micron in order to target the stratospheric emissions of CH4 (methane), C2H4 (ethylene), C2H6 (ethane) and C2H2 (acetylene), respectively.  Such spectra are inverted using the NEMESIS radiative transfer software (Irwin et al., 2008, JQSRT 109, 1136) to derive spatial variations in the vertical profiles of temperature, C2H2, C2H4 and C2H6 and the vertical location of the hydrocarbon homopause.  We will present these results, in addition to those derived from previous measurements, in order to highlight the thermal, chemical and dynamical evolution of Jupiter’s polar stratosphere.  As part of a new project, TEXES spectra were also recorded in settings centered at 10.95, 11.83 and 13.37 with the goal of detecting CH2CCH2 (allene), C3H6 (propene) and C3H8 (propane).  We will present these spectra to indicate whether these species have been detected.   Detected spectral features will be inverted to derive vertical and spatial variations in its abundance.  In the case of a non-detection, an upper limit would be derived.  The presence or absence of such hydrocarbon species would provide unique insight into how auroral processes modify the chemistry of Jupiter’s stratosphere.