Publications by Patrick Irwin

Seasonal Evolution of Titan's Stratosphere During the Cassini Mission


NA Teanby, M Sylvestre, J Sharkey, CA Nixon, S Vinatier, PGJ Irwin

Wave Activity in Jupiter's North Equatorial Belt From Near-Infrared Reflectivity Observations

Geophysical Research Letters 46 (2019) 1232-1241

RS Giles, GS Orton, AW Stephens, MH Wong, PGJ Irwin, JA Sinclair, F Tabataba-Vakili

©2019. American Geophysical Union. All Rights Reserved. High spatial resolution images of Jupiter at 1.58–2.28 μm are used to track and characterize a wave pattern observed in 2017 at a planetocentric latitude of 14°N. The wave pattern has a wave number of 18 and spans ∼5° in latitude. One bright crest remains stationary in System III longitude, while the remaining crests move slowly westward. The bright and dark regions of the near-infrared wave pattern are caused by variations in the vertical location of the upper tropospheric haze layer. A comparison with thermal infrared observations shows a correlation with temperature anomalies in the upper troposphere. The results are consistent with a Rossby wave, generated by flow around a stationary vortex.

Abundance measurements of Titan's stratospheric HCN, HC3N, C3H4, and CH3CN from ALMA observations

Icarus 319 (2019) 417-432

AE Thelen, CA Nixon, NJ Chanover, MA Cordiner, EM Molter, NA Teanby, PGJ Irwin, J Serigano, SB Charnley

© 2018 Elsevier Inc. Previous investigations have employed more than 100 close observations of Titan by the Cassini orbiter to elucidate connections between the production and distribution of Titan's vast, organic-rich chemical inventory and its atmospheric dynamics. However, as Titan transitions into northern summer, the lack of incoming data from the Cassini orbiter presents a potential barrier to the continued study of seasonal changes in Titan's atmosphere. In our previous work (Thelen et al., 2018), we demonstrated that the Atacama Large Millimeter/submillimeter Array (ALMA) is well suited for measurements of Titan's atmosphere in the stratosphere and lower mesosphere (∼100−500 km) through the use of spatially resolved (beam sizes < 1′′) flux calibration observations of Titan. Here, we derive vertical abundance profiles of four of Titan's trace atmospheric species from the same 3 independent spatial regions across Titan's disk during the same epoch (2012–2015): HCN, HC3N, C3H4, and CH3CN. We find that Titan's minor constituents exhibit large latitudinal variations, with enhanced abundances at high latitudes compared to equatorial measurements; this includes CH3CN, which eluded previous detection by Cassini in the stratosphere, and thus spatially resolved abundance measurements were unattainable. Even over the short 3-year period, vertical profiles and integrated emission maps of these molecules allow us to observe temporal changes in Titan's atmospheric circulation during northern spring. Our derived abundance profiles are comparable to contemporary measurements from Cassini infrared observations, and we find additional evidence for subsidence of enriched air onto Titan's south pole during this time period. Continued observations of Titan with ALMA beyond the summer solstice will enable further study of how Titan's atmospheric composition and dynamics respond to seasonal changes.

Ethane in Titan's Stratosphere from Cassini CIRS Far- and Mid-infrared Spectra


NA Lombardo, CA Nixon, M Sylvestre, DE Jennings, N Teanby, PJG Irwin, FM Flasar

Constraints on Uranus's haze structure, formation and transport

Icarus Elsevier BV 333 (2019) 1-11

D Toledo, PGJ Irwin, P Rannou, NA Teanby, AA Simon, MH Wong, GS Orton

Measurement of CH3D on Titan at Submillimeter Wavelengths


AE Thelen, CA Nixon, MA Cordiner, SB Charnley, PGJ Irwin, Z Kisiel

A brightening of Jupiter’s auroral 7.8-μm CH <inf>4</inf> emission during a solar-wind compression

Nature Astronomy (2019)

JA Sinclair, GS Orton, J Fernandes, Y Kasaba, TM Sato, T Fujiyoshi, C Tao, MF Vogt, D Grodent, B Bonfond, JI Moses, TK Greathouse, W Dunn, RS Giles, F Tabataba-Vakili, LN Fletcher, PGJ Irwin

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Enhanced mid-infrared emission from CH 4 and other stratospheric hydrocarbons has been observed coincident with Jupiter’s ultraviolet auroral emission 1–3 . This suggests that auroral processes and the neutral stratosphere of Jupiter are coupled; however, the exact nature of this coupling is unknown. Here we present a time series of Subaru-COMICS images of Jupiter measured at a wavelength of 7.80 μm on 11–14 January, 4–5 February and 17–20 May 2017. These data show that both the morphology and magnitude of the auroral CH 4 emission vary on daily timescales in relation to external solar-wind conditions. The southern auroral CH 4 emission increased in brightness temperature by about 3.8 K between 15:50 ut, 11 January and 12:57 ut, 12 January, during a predicted solar-wind compression. During the same compression, the northern auroral emission exhibited a duskside brightening, which mimics the morphology observed in the ultraviolet auroral emission during periods of enhanced solar-wind pressure 4,5 . These results suggest that changes in external solar-wind conditions perturb the Jovian magnetosphere in such a way that energetic particles are accelerated into the planet’s atmosphere, deposit their energy as deep as the neutral stratosphere, and modify the thermal structure, the abundance of CH 4 or the population of energy states of CH 4 . We also find that the northern and southern auroral CH 4 emission evolved independently between the January, February and May images, as has been observed at X-ray wavelengths over shorter timescales 6 and at mid-infrared wavelengths over longer timescales 7 .

Corrigendum to “Neptune's carbon monoxide profile and phosphine upper limits from Herschel/SPIRE” (Icarus, vol 319, p86–98, 2019) (Icarus (2019) 319 (86–98), (S0019103518304457), (10.1016/j.icarus.2018.09.014))

Icarus 322 (2019) 261-261

NA Teanby, PGJ Irwin, JI Moses

© 2018 The authors would like to publish the below information which was incorrectly published in its original version. Page 90: The equation for saturation vapour pressure should be PSVP(T) =exp(a+b/T +cT). Page92: TheD/HratiomeasuredbyFeuchtgruberetal.(2013)fromHerschelPACSshouldbe 4.1±0.4×10−5. References Feuchtgruber, H., Lellouch, E., Orton, G., de Graauw, T., Vandenbussche, B., Swinyard, B., Moreno, R., Jarchow, C., Billebaud, F., Cavali´e, T., Sidher, S., Hartogh, P., 2013. The D/H ratio in the atmospheres of Uranus and Neptune from Herschel-PACS observations. Astron. Astrophys. 551, 1–9.

Jupiter's auroral-related stratospheric heating and chemistry III: Abundances of C <inf>2</inf> H <inf>4</inf> , CH <inf>3</inf> C <inf>2</inf> H, C <inf>4</inf> H <inf>2</inf> and C <inf>6</inf> H <inf>6</inf> from Voyager-IRIS and Cassini-CIRS

Icarus 328 (2019) 176-193

JA Sinclair, JI Moses, V Hue, TK Greathouse, GS Orton, LN Fletcher, PGJ Irwin

© 2019 Elsevier Inc. We present an analysis of Voyager-1-IRIS and Cassini-CIRS spectra of Jupiter's high latitudes acquired during the spacecrafts' respective flybys in November 1979 and January 2001. We performed a forward-model analysis in order to derive the abundances of ethylene (C 2 H 4 ), methylacetylene (CH 3 C 2 H), diacetylene (C 4 H 2 ) and benzene (C 6 H 6 ) in Jupiter's northern and southern auroral regions. We also compared these abundances to: 1) lower-latitude abundances predicted by the Moses et al. (2005) ‘Model A’ photochemical model, henceforth ‘Moses 2005A’, and 2) abundances derived at non-auroral longitudes in the same latitude band. This paper serves as an extension of Sinclair et al. (2017b), where we retrieved the vertical profiles of temperature, C 2 H 2 and C 2 H 6 from similar datasets. We find that an enrichment of C 2 H 4 , CH 3 C 2 H and C 6 H 6 with respect to lower-latitude abundances is required to fit the spectra of Jupiter's northern and southern auroral regions. For example, for CIRS 0.5 cm −1 spectra of Jupiter's southern auroral region, scale factor enrichments of 6.40 −1.15+1.30 and 9.60 −3.67+3.98 are required with respect to the Moses 2005A vertical profiles of C 2 H 4 and C 6 H 6 , respectively, in order to fit the spectral emission features of these species at ∼950 and ∼674 cm −1 . Similarly, in order to fit the CIRS 2.5 cm −1 spectra of Jupiter's northern auroral region, scale factor enrichments of 1.60 −0.21+0.37 , 3.40 −1.69+1.89 and 15.00 −4.02+4.01 with respect to the Moses 2005A vertical profiles of C 2 H 4 , CH 3 C 2 H and C 6 H 6 were required, respectively. Outside of Jupiter's auroral region in the same latitude bands, only upper-limit abundances of C 2 H 4 , CH 3 C 2 H and C 6 H 6 could be determined due to the limited sensitivity of the measurements, the weaker emission features combined with cooler stratospheric temperatures (and therefore decreased thermal emission) of these regions. Nevertheless, for a subset of the observations, derived abundances of C 2 H 4 and C 6 H 6 in Jupiter's auroral regions were higher (by 1 σ) with respect to upper-limit abundances derived outside the auroral region in the same latitude band. This is suggestive that the influx of energetic ions and electrons from the Jovian magnetosphere and external solar-wind environment into the neutral atmosphere in Jupiter's auroral regions drives enhanced ion-related chemistry, as has also been inferred from Cassini observations of Saturn's high latitudes (Fletcher et al., 2018; Guerlet et al., 2015; Koskinen et al., 2016). We were not able to constrain the abundance of C 4 H 2 in either Jupiter's auroral regions or non-auroral regions due to its lower (predicted) abundance and weaker emission feature. Thus, only upper-limit abundances were derived in both locations. From CIRS 2.5 cm −1 spectra, the upper limit abundance of C 4 H 2 corresponds to a scale factor enhancement of 45.6 and 23.8 with respect to the Moses 2005A vertical profile in Jupiter's non-auroral and auroral regions.

Hazes and clouds in a singular triple vortex in Saturn's atmosphere from HST/WFC3 multispectral imaging

Icarus 333 (2019) 22-36

JF Sanz-Requena, S Pérez-Hoyos, A Sánchez-Lavega, T del Rio-Gaztelurrutia, PGJ Irwin

© 2019 In this paper we present a study of the vertical haze and cloud structure over a triple vortex in Saturn's atmosphere in the planetographic latitude range 55°N-69°N (del Río-Gaztelurrutia et al., 2018)using HST/WFC3 multispectral imaging. The observations were taken during 29–30 June and 1 July 2015 at ten different filters covering spectral range from the 225 nm to 937 nm, including the deep methane band at 889 nm. Absolute reflectivity measurements of this region at all wavelengths and under a number of illumination and observation geometries are fitted with the values produced by a radiative transfer model. Most of the reflectivity variations in this wavelength range can be attributed to changes in the tropospheric haze. The anticyclones are optically thicker (τ ~25 vs ~10), more vertically extended (~3 gas scale heights vs ~2)and their bases are located deeper in the atmosphere (550 mbar vs 500 mbar)than the cyclone.

Spatial and seasonal variations in C_3/H_x hydrocarbon abundance in Titan's stratosphere from Cassini CIRS observations

Icarus 317 (2019) 454-469

NA Lombardo, CA Nixon, RK Achterberg, A Jolly, K Sung, PGJ Irwin, FM Flasar

© 2018 Of the C3Hxhydrocarbons, propane (C3H8) and propyne (methylacetylene, CH3C2H) were first detected in Titan's atmosphere during the Voyager 1 flyby in 1980. Propene (propylene, C3H6) was first detected in 2013 with data from the Composite InfraRed Spectrometer (CIRS) instrument on Cassini. We present the first measured abundance profiles of propene on Titan from radiative transfer modeling, and compare our measurements to predictions derived from several photochemical models. Near the equator, propene is observed to have a peak abundance of 10 ppbv at a pressure of 0.2 mbar. Several photochemical models predict the amount at this pressure to be in the range 0.3–1 ppbv and also show a local minimum near 0.2 mbar which we do not see in our measurements. We also see that propene follows a different latitudinal trend than the other C3molecules. While propane and propyne concentrate near the winter pole, transported via a global convective cell, propene is most abundant above the equator. We retrieve vertical abundances profiles between 125 km and 375 km for these gases for latitude averages between 60°S–20°S, 20°S–20°N, and 20°N–60°N over two time periods, 2004 through 2009 representing Titan's atmosphere before the 2009 equinox, and 2012 through 2015 representing time after the equinox. Additionally, using newly corrected line data, we determined an updated upper limit for allene (propadiene, CH2CCH2, the isomer of propyne). We claim a 3-σ upper limit mixing ratio of 2.5 × 10−9 within 30° of the equator. The measurements we present will further constrain photochemical models by refining reaction rates and the transport of these gases throughout Titan's atmosphere.

Probable detection of hydrogen sulphide (H2S) in Neptune's atmosphere

ICARUS 321 (2019) 550-563

PGJ Irwin, D Toledo, R Garland, NA Teanby, LN Fletcher, GS Orton, B Bezard

Analysis of gaseous ammonia (NH3) absorption in the visible spectrum of Jupiter - Update

ICARUS 321 (2019) 572-582

PGJ Irwin, N Bowles, AS Braude, R Garland, S Calcutt, PA Coles, SN Yurchenko, J Tennyson

Neptune's carbon monoxide profile and phosphine upper limits from Herschel/SPIRE: Implications for interior structure and formation

ICARUS 319 (2019) 86-98

NA Teanby, PGJ Irwin, JI Moses

Latitudinal variation in the abundance of methane (CH <inf>4</inf> )above the clouds in Neptune's atmosphere from VLT/MUSE Narrow Field Mode Observations

Icarus 331 (2019) 69-82

PGJ Irwin, D Toledo, AS Braude, R Bacon, PM Weilbacher, NA Teanby, LN Fletcher, GS Orton

© 2019 The Authors Observations of Neptune, made in 2018 using the new Narrow Field Adaptive Optics mode of the Multi Unit Spectroscopic Explorer (MUSE)instrument at the Very Large Telescope (VLT)from 0.48 to 0.93 μm, are analysed here to determine the latitudinal and vertical distribution of cloud opacity and methane abundance in Neptune's observable troposphere (0.1–∼ 3bar). Previous observations at these wavelengths in 2003 by HST/STIS (Karkoschka and Tomasko 2011, Icarus 205, 674–694)found that the mole fraction of methane above the cloud tops (at ∼ 2 bar)varied from ∼ 4% at equatorial latitudes to ∼ 2% at southern polar latitudes, by comparing the observed reflectivity at wavelengths near 825 nm controlled primarily by either methane absorption or H 2 –H 2 /H 2 –He collision-induced absorption. We find a similar variation in cloud-top methane abundance in 2018, which suggests that this depletion of methane towards Neptune's pole is potentially a long-lived feature, indicative of long-term upwelling at mid-equatorial latitudes and subsidence near the poles. By analysing these MUSE observations along the central meridian with a retrieval model, we demonstrate that a broad boundary between the nominal and depleted methane abundances occurs at between 20 and 40°S. We also find a small depletion of methane near the equator, perhaps indicating subsidence there, and a local enhancement near 60–70°S, which we suggest may be associated with South Polar Features (SPFs)seen in Neptune's atmosphere at these latitudes. Finally, by the use of both a reflectivity analysis and a principal component analysis, we demonstrate that this depletion of methane towards the pole is apparent at all locations on Neptune's disc, and not just along its central meridian.

Haze and cloud structure of Saturn's North Pole and Hexagon Wave from Cassini/ISS imaging

Icarus (2018)

JF Sanz-Requena, S Pérez-Hoyos, A Sánchez-Lavega, A Antuñano, PGJ Irwin

© 2017 Elsevier Inc. In this paper we present a study of the vertical haze and cloud structure in the upper two bars of Saturn's Northern Polar atmosphere using the Imaging Science Subsystem (ISS) instrument onboard the Cassini spacecraft. We focus on the characterization of latitudes from 53° to 90° N. The observations were taken during June 2013 with five different filters (VIO, BL1, MT2, CB2 and MT3) covering spectral range from the 420 nm to 890 nm (in a deep methane absorption band). Absolute reflectivity measurements of seven selected regions at all wavelengths and several illumination and observation geometries are compared with the values produced by a radiative transfer model. The changes in reflectivity at these latitudes are mostly attributed to changes in the tropospheric haze. This includes the haze base height (from 600 ± 200 mbar at the lowest latitudes to 1000 ± 300 mbar in the pole), its particle number density (from 20 ± 2 particles/cm 3 to 2 ± 0.5 particles/cm 3 at the haze base) and its scale height (from 18 ± 0.1 km to 50 ± 0.1 km). We also report variability in the retrieved particle size distribution and refractive indices. We find that the Hexagonal Wave dichotomizes the studied stratospheric and tropospheric hazes between the outer, equatorward regions and the inner, Polar Regions. This suggests that the wave or the jet isolates the particle distribution at least at tropospheric levels.

A chemical survey of exoplanets with ARIEL


G Tinetti, P Drossart, P Eccleston, P Hartogh, A Heske, J Leconte, G Micela, M Ollivier, G Pilbratt, L Puig, D Turrini, B Vandenbussche, P Wolkenberg, J-P Beaulieu, LA Buchave, M Ferus, M Griffin, M Guedel, K Justtanont, P-O Lagage, P Machado, G Malaguti, M Min, HU Norgaard-Nielsen, M Rataj, T Ray, I Ribas, M Swain, R Szabo, S Werner, J Barstow, M Burleigh, J Cho, VC du Foresto, A Coustenis, L Decin, T Encrenaz, M Galand, M Gillon, R Helled, J Carlos Morales, AG Munoz, A Moneti, I Pagano, E Pascale, G Piccioni, D Pinfield, S Sarkar, F Selsis, J Tennyson, A Triaud, O Venot, I Waldmann, D Waltham, G Wright, J Amiaux, J-L Augueres, M Berthe, N Bezawada, G Bishop, N Bowles, D Coffey, J Colome, M Crook, P-E Crouzet, V Da Peppo, IE Sanz, M Focardi, M Frericks, T Hunt, R Kohley, K Middleton, G Morgante, R Ottensamer, E Pace, C Pearson, R Stamper, K Symonds, M Rengel, E Renotte, P Ade, L Affer, C Alard, N Allard, F Altieri, Y Andre, C Arena, I Argyriou, A Aylward, C Baccani, G Bakos, M Banaszkiewicz, M Barlow, V Batista, G Bellucci, S Benatti, P Bernardi, B Bezard, M Blecka, E Bolmont, B Bonfond, R Bonito, AS Bonomo, JR Brucato, AS Brun, I Bryson, W Bujwan, S Casewell, B Charnay, CC Pestellini, G Chen, A Ciaravella, R Claudi, R Cledassou, M Damasso, M Damiano, C Danielski, P Deroo, AM Di Giorgio, C Dominik, V Doublier, S Doyle, R Doyon, B Drummond, B Duong, S Eales, B Edwards, M Farina, E Flaccomio, L Fletcher, F Forget, S Fossey, M Fraenz, Y Fujii, A Garcia-Piquer, W Gear, H Geoffray, JC Gerard, L Gesa, H Gomez, R Graczyk, C Griffith, D Grodent, MG Guarcello, J Gustin, K Hamano, P Hargrave, Y Hello, K Heng, E Herrero, A Hornstrup, B Hubert, S Ida, M Ikoma, N Iro, P Irwin, C Jarchow, J Jaubert, H Jones, Q Julien, S Kameda, F Kerschbaum, P Kervella, T Koskinen, M Krijger, N Krupp, M Lafarga, F Landini, E Lellouch, G Leto, A Luntzer, T Rank-Luftinger, A Maggio, J Maldonado, J-P Maillard, U Mall, J-B Marquette, S Mathis, P Maxted, T Matsuo, A Medvedev, Y Miguel, V Minier, G Morello, A Mura, N Narita, V Nascimbeni, N Nguyen Tong, V Noce, F Oliva, E Palle, P Palmer, M Pancrazzi, A Papageorgiou, V Parmentier, M Perger, A Petralia, S Pezzuto, R Pierrehumbert, I Pillitteri, G Piotto, G Pisano, L Prisinzano, A Radioti, J-M Reess, L Rezac, M Rocchetto, A Rosich, N Sanna, A Santerne, G Savini, G Scandariato, B Sicardy, C Sierra, G Sindoni, K Skup, I Snellen, M Sobiecki, L Soret, A Sozzetti, A Stiepen, A Strugarek, J Taylor, W Taylor, L Terenzi, M Tessenyi, A Tsiaras, C Tucker, D Valencia, G Vasisht, A Vazan, F Vilardell, S Vinatier, S Viti, R Waters, P Wawer, A Wawrzaszek, A Whitworth, YL Yung, SN Yurchenko, MR Zapatero Osorio, R Zellem, T Zingales, F Zwart

A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex.

Nature communications 9 (2018) 3564-

LN Fletcher, GS Orton, JA Sinclair, S Guerlet, PL Read, A Antuñano, RK Achterberg, FM Flasar, PGJ Irwin, GL Bjoraker, J Hurley, BE Hesman, M Segura, N Gorius, A Mamoutkine, SB Calcutt

Saturn's polar stratosphere exhibits the seasonal growth and dissipation of broad, warm vortices poleward of ~75° latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini's reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly formed NPSV was bounded by a strengthening stratospheric thermal gradient near 78°N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn's long-lived polar hexagon-which was previously expected to be trapped in the troposphere-can influence the stratospheric temperatures some 300 km above Saturn's clouds.

Detectability of Biosignatures in Anoxic Atmospheres with the James Webb Space Telescope: A TRAPPIST-1e Case Study


J Krissansen-Totton, R Garland, P Irwin, DC Catling

Seasonal evolution of C2N2, C3H4, and C4H2 abundances in Titan's lower stratosphere


M Sylvestre, NA Teanby, S Vinatier, S Lebonnois, PGJ Irwin