Publications by Patrick Irwin


Uranus in Northern Midspring: Persistent Atmospheric Temperatures and Circulations Inferred from Thermal Imaging

The Astronomical Journal American Astronomical Society 159 (0) 45-45

MT Roman, LN Fletcher, GS Orton, N Rowe-Gurney, PGJ Irwin


2.5-D retrieval of atmospheric properties from exoplanet phase curves: Application to WASP-43b observations

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) (0)

PGJ Irwin, V Parmentier, J Taylor, J Barstow, S Aigrain, GKH Lee, R Garland

We present a novel retrieval technique that attempts to model phase curve observations of exoplanets more realistically and reliably, which we call the 2.5-dimension (2.5-D) approach. In our 2.5-D approach we retrieve the vertical temperature profile and mean gaseous abundance of a planet at all longitudes and latitudes \textbf{simultaneously}, assuming that the temperature or composition, $x$, at a particular longitude and latitude $(\Lambda,\Phi)$ is given by $x(\Lambda,\Phi) = \bar{x} + (x(\Lambda,0) - \bar{x})\cos^n\Phi$, where $\bar{x}$ is the mean of the morning and evening terminator values of $x(\Lambda,0)$, and $n$ is an assumed coefficient. We compare our new 2.5-D scheme with the more traditional 1-D approach, which assumes the same temperature profile and gaseous abundances at all points on the visible disc of a planet for each individual phase observation, using a set of synthetic phase curves generated from a GCM-based simulation. We find that our 2.5-D model fits these data more realistically than the 1-D approach, confining the hotter regions of the planet more closely to the dayside. We then apply both models to WASP-43b phase curve observations of HST/WFC3 and Spitzer/IRAC. We find that the dayside of WASP-43b is apparently much hotter than the nightside and show that this could be explained by the presence of a thick cloud on the nightside with a cloud top at pressure $< 0.2$ bar. We further show that while the mole fraction of water vapour is reasonably well constrained to $(1-10)\times10^{-4}$, the abundance of CO is very difficult to constrain with these data since it is degenerate with temperature and prone to possible systematic radiometric differences between the HST/WFC3 and Spitzer/IRAC observations. Hence, it is difficult to reliably constrain C/O.


C2N2 vertical profile in Titan’s stratosphere

The Astronomical Journal American Astronomical Society (0)

M Sylvestre, N Teanby, M Dobrijevic, J Sharkey, P Irwin


The Transiting Exoplanet Community Early Release Science Program for JWST

Planetary and Space Science Elsevier (0)

JL Bean, KB Stevenson, NM Batalha, Z Berta-Thompson, L Kreidberg, N Crouzet, B Benneke, MR Line, DK Sing, HR Wakeford, HA Knutson, EM-R Kempton, J-M Désert, I Crossfield, NE Batalha, JD Wit, V Parmentier, J Harrington, JI Moses, M Lopez-Morales, MK Alam, J Blecic, G Bruno, AL Carter, JW Chapman, L Decin, D Dragomir, TM Evans, JJ Fortney, JD Fraine, P Gao, AG Muñoz, NP Gibson, JM Goyal, K Heng, R Hu, S Kendrew, BM Kilpatrick, J Krick, P-O Lagage, M Lendl, T Louden, N Madhusudhan, AM Mandell, M Mansfield, EM May, G Morello, CV Morley, N Nikolov, S Redfield, JE Roberts, E Schlawin, JJ Spake, KO Todorov, A Tsiaras, O Venot, WC Waalkes, PJ Wheatley, RT Zellem, D Angerhausen, D Barrado, L Carone, SL Casewell, PE Cubillos, M Damiano, MD Val-Borro, B Drummond, B Edwards, M Endl, N Espinoza, K France, JE Gizis, TP Greene, TK Henning, Y Hong, JG Ingalls, N Iro, PGJ Irwin, T Kataria, F Lahuis, J Leconte, J Lillo-Box, S Lines, JD Lothringer, L Mancini, F Marchis, N Mayne, E Palle, E Rauscher, G Roudier, EL Shkolnik, J Southworth, MR Swain, J Taylor, J Teske, G Tinetti, P Tremblin, GS Tucker, RV Boekel, IP Waldmann, IC Weaver, T Zingales

The James Webb Space Telescope (JWST) presents the opportunity to transform our understanding of planets and the origins of life by revealing the atmospheric compositions, structures, and dynamics of transiting exoplanets in unprecedented detail. However, the high-precision, time-series observations required for such investigations have unique technical challenges, and prior experience with other facilities indicates that there will be a steep learning curve when JWST becomes operational. In this paper we describe the science objectives and detailed plans of the Transiting Exoplanet Community Early Release Science (ERS) Program, which is a recently approved program for JWST observations early in Cycle 1. The goal of this project, for which the obtained data will have no exclusive access period, is to accelerate the acquisition and diffusion of technical expertise for transiting exoplanet observations with JWST, while also providing a compelling set of representative datasets that will enable immediate scientific breakthroughs. The Transiting Exoplanet Community ERS Program will exercise the time-series modes of all four JWST instruments that have been identified as the consensus highest priorities, observe the full suite of transiting planet characterization geometries (transits, eclipses, and phase curves), and target planets with host stars that span an illustrative range of brightnesses. The observations in this program were defined through an inclusive and transparent process that had participation from JWST instrument experts and international leaders in transiting exoplanet studies. Community engagement in the project will be centered on a two-phase Data Challenge that culminates with the delivery of planetary spectra, time-series instrument performance reports, and open-source data analysis toolkits in time to inform the agenda for Cycle 2 of the JWST mission.


Modelling the expected observations of the Advanced Ice Giants Net Flux Radiometer (IG-NFR) instrument concept, under study for future entry probe missions to Uranus or Neptune.

Copernicus GmbH (0)

P Irwin, S Calcutt, J Dobinson, J Alday, A James, M Roos-Serote, S Aslam, C Nixon, G Villanueva

<jats:p>&amp;lt;p&amp;gt;The NASA Ice Giants Pre-Decadal Survey Mission Report (2017) recommended the high scientific importance of sending a mission with an orbiter and a probe to one of the Ice Giants, with preferential launch dates in the 2029-2034 timeframe. Such a mission concept is equally well supported by European scientists and Mousis et al (P&amp;amp;SS, 155, 12, 2018) give compelling scientific rationales for the exploration of these worlds with missions carrying in situ probes.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;In this presentation&amp;amp;#160;we will outline the conceptual design of the Advanced Ice Giants Net Flux Radiometer (IG-NFR) instrument, currently being designed by NASA Goddard Space Flight Center to make in situ observations of the upward and downward fluxes of solar and thermal radiation in the atmospheres of Uranus and Neptune. The IG-NFR is designed to: (i) accommodate seven filter bandpass channels in the spectral range 0.25-300 &amp;amp;#181;m (ii) measure up and down radiation flux in a clear unobstructed 10&amp;amp;#176; FOV for each channel; (iii) use thermopile detectors that can measure a change of flux of at least 0.5 W/m&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt; per decade of pressure; (iv) view five distinct view angles (&amp;amp;#177;80&amp;amp;#176;, &amp;amp;#177;45&amp;amp;#176;, and 0&amp;amp;#176;); (v) predict the detector response with changing&amp;amp;#160; temperature environment; (vi) use application-specific integrated circuit technology for the thermopile detector readout; (vii) be able to integrate radiance for 2s or longer, and (vii) sample each view angle including calibration targets. The IG-NFR system noise equivalent power at 298 K is 73 pW in a 1 Hz electrical bandwidth.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;We present initial simulations of the anticipated observations using two radiative transfer and retrieval tools, NEMESIS (Irwin et al., JQSRT, 109, 1136, 2008) and the Planetary Spectrum Generator (PSG, Villanueva et al., 2017, https://psg.gsfc.nasa.gov). For the NEMESIS modelling the radiative fluxes observable at varying pressure levels were calculated with a Matrix-Operator plane-parallel multiple-scattering model, using between 5 and 21 zenith angle quadrature points and up to 38 Fourier components for the azimuth decomposition. We also employed PSG to further validate our flux estimates, providing an important benchmarking and comparison test between both models. PSG solves the scattering radiative transfer employing the discrete ordinates method, with the scattering phase function described in terms of an expansion in terms of Legendre Polynomials. Molecular cross-sections are solved via the correlated-k method employing the latest HITRAN database (Gordon et al., 2017), which are completed with the latest collision-induced-absorption (CIA, Karman et al., 2019), and UV/optical cross-sections from the MPI database (Keller-Rudek et al., 2013). For the nominal case the Sun was assumed to be at an altitude of 10&amp;amp;#176; above the horizon. The internal radiance field was calculated at each internal level for a standard reference Uranus atmosphere (e.g., Irwin et al., 2017) with the addition of a single cloud layer, based at 3 bar and composed of particles with a mean radius of 1.0 &amp;amp;#181;m (and size variance 0.1) and assumed complex refractive index of 1.4 + 0.001i at all wavelengths. The opacity and fractional scale height of this cloud were fitted in both models to match the combined near-infrared observations of HST/WFC3, IRTF/SpeX and VLT/SINFONI analyzed by Irwin et al. (2017). The internal radiance fields were calculated from 0.4 to 300 &amp;amp;#181;m using this atmospheric model.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;We will show how these simulations are being used to guide the choice of spectral filter bandwidths and centres to optimize the scientific return of such an instrument. We will show that observations with such an instrument can be used to constrain effectively the radiation energy budget in the atmospheres of the Ice Giants and can also be used to determine the pressures of cloud and haze layers and broadly constrain particle size. Such modelling also allows us to simulate the visible appearance of Uranus&amp;amp;#8217; atmosphere during a descent and to perform detailed validations of the simulations by comparing the two radiative transfer models (NEMESIS and PSG).&amp;lt;/p&amp;gt;</jats:p>


Isotopic composition of water vapour in the Martian atmosphere: vertical profiles from ACS MIR on ExoMars TGO

Copernicus GmbH (0)

J Alday, PGJ Irwin, CF Wilson, KS Olsen, L Baggio, F Montmessin, O Korablev, A Trokhimovskiy, AA Fedorova, DA Belyaev, A Shakun, A Patrakeev, A Grigoriev


Modelling the in situ solar and thermal radiation environment for future entry probe missions to Venus

Copernicus GmbH (0)

P Irwin, C Wilson, J Alday, M Roos-Serote, J Barstow, S Aslam

<jats:p>&amp;lt;p&amp;gt;In this presentation we will describe recent work to model upward and downward fluxes of solar and thermal radiation in the atmosphere of Venus using the NEMESIS radiative transfer and retrieval tool (Irwin et al., JQSRT, 109, 1136, 2008). Using a plane-parallel matrix operator multiple-scattering model we simulate the internal 3D radiation field within Venus&amp;amp;#8217; atmosphere and compare our simulations with the observations of the Pioneer Venus&amp;amp;#160;and Venera 13 and 14 entry probes. Such simulations allow us to assess the availability of sunlight and the visibility of the sun azimuth direction in the cloud layer for potential balloon missions, and also enables us to predict at what altitude the surface will become visible for probes descending on dayside. A reanalysis of the Venera 13 and 14 radiance spectra observations will be used to reassess earlier estimates of cloud structure and water vapour abundance. Such modelling also allows us to simulate the visible appearance of Venus&amp;amp;#8217; atmosphere during the descent of a probe mission as will be shown.&amp;lt;/p&amp;gt;</jats:p>


Limb-darkening reanalysis of latitudinal variation of cloud-top methane abundance in Neptune's atmosphere from VLT/MUSE-NFM

Copernicus GmbH (0)

P Irwin, J Dobinson, A James, D Toledo, N Teanby, L Fletcher, G Orton, S Perez-Hoyos


Longitudinal Variations in the Stratosphere of Uranus from the Spitzer Infrared Spectrometer

Copernicus GmbH (0)

N Rowe-Gurney, LN Fletcher, GS Orton, MT Roman, A Mainzer, JI Moses, I de Pater, PGJ Irwin

<jats:p>&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Introduction:&amp;lt;/strong&amp;gt; NASA&amp;amp;#8217;s Spitzer Infrared Spectrometer (IRS) acquired mid-infrared (5-37 &amp;amp;#956;m) disc-averaged spectra of Uranus very near its equinox over 21.7 hours on 16th to 17th of December 2007. A global-mean spectrum was constructed from observations of multiple longitudes, spaced equally around the planet, and have provided the opportunity for the most comprehensive globally averaged characterisation of Uranus&amp;amp;#8217; temperature and composition ever obtained (Orton et al., 2014 a, b). In this work, we analyse the disc-averaged spectra at four separate longitudes to shed light on the discovery of longitudinal variability occurring in Uranus&amp;amp;#8217; stratosphere during the 2007 equinox.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;The composition and temperature structure of Uranus&amp;amp;#8217; stratosphere is dominated by methane photolysis in the upper stratosphere (Moses et al., 2018). The complex hydrocarbons produced in these solar-driven reactions are the main trace gases present in the stratosphere and upper troposphere. These species are observable at mid-infrared wavelengths sensitive to altitudes between around one nanobar and two bars of pressure (Orton et al., 2014a).&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Due to Uranus&amp;amp;#8217; extremely high obliquity we can only clearly observe its longitudinal variation in disc-averaged observations close to its equinox. The northern spring equinox occurred in December 2007 with the aforementioned Spitzer observations occurring just 10 days after. The Spitzer data have been re-analysed using the most up to date pipeline available from NASA&amp;amp;#8217;s Spitzer Science Centre, resulting in minor changes over the previous reduction.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Longitudinal Variation:&amp;lt;/strong&amp;gt; We assess the variations in discrete channels sensitive to different emission features. The radiances inside each interval are averaged and compared to the mean of all four longitudes. Each instrument module is exposed at a different time causing a spread of data points across the multiple longitudes displayed in Figure 1.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;We detect a variability of up to 15% at stratospheric altitudes sensitive to the hydrocarbon species at around the 0.1-mbar pressure level. The tropospheric hydrogen-helium continuum and the monodeuterated methane that also arises from these deeper levels, both exhibit a negligible variation smaller than 2%, constraining the phenomenon to the stratosphere. Observations from Keck II NIRCII in December 2007 (Sromovsky et al., 2009; de Pater et al., 2011) and VLT/VISIR in 2009 (Roman et al. 2020) suggest possible links to these variations in the form of discrete meteorological features. In particular, Roman et al. (2020) identified discrete patches of brightness in 13-&amp;amp;#956;m (acetylene) emission within a broad stratospheric band at mid-latitudes, which could be related to the variability observed by Spitzer.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Optimal Estimation Retrievals:&amp;lt;/strong&amp;gt; Building on the forward-modelling analysis of the global average study, we present full optimal estimation inversions (using the NEMESIS retrieval algorithm, Irwin et al., 2008) of the low-resolution spectra at each longitude to distinguish between thermal and compositional variability. The model suggests that variations can be explained solely by changes in stratospheric temperatures. A temperature change of less than 2 K is needed to model the observed variation. This is compounded by results from high-resolution forward models (primarily sounding the ethane and acetylene emission) constructed using the parameters retrieved from the low-resolution spectra.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;The data were best reproduced by models with atmospheric mixing via eddy diffusion that was weaker than that assumed by Orton et al. but still within the confines of a realistic fit according to their model. An eddy diffusion coefficient value of 1020 cm&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;sec&amp;lt;sup&amp;gt;-1&amp;lt;/sup&amp;gt; and a tropopause methane mole fraction of 8.0x10&amp;lt;sup&amp;gt;-5&amp;lt;/sup&amp;gt; provides the best fit to the temperature structure and the methane vertical profile whilst also maintaining the closest chi-squared value for the spectral fit (Moses et al., 2018).&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Conclusion:&amp;lt;/strong&amp;gt; The longitudinal variation detected at Uranus during the 2007 equinox is an observed physical change in the stratosphere of the planet, most likely a temperature change associated with the band of bright stratospheric emission observed in ground-based images. The Spitzer IRS data can provide much detail but without accompanying spatial resolution it is impossible to come to a definitive conclusion as to the origins of the changes.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;The James Webb Space Telescope, when it launches in 2021, will provide much improved spectral and spatial resolution needed in the mid-infrared band to provide answers to the causes of the observed variation.&amp;lt;/p&amp;gt;</jats:p>


Sub-Seasonal Variations in Neptune's Stratospheric Infrared Emission from VLT-VISIR, 2006-2018

Copernicus GmbH (0)

MT Roman, LN Fletcher, GS Orton, J Vatant d'Ollone, JA Sinclair, N Rowe-Gurney, J Moses, PGJ Irwin


Neptune and Uranus: ice or rock giants?

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences Royal Society, The (0)

N Teanby, P Irwin, J Moses, R Hellad


ORTIS Design and development report

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PG Irwin, B Ellison, S Calcutt


Third report on sub-millimetre spectra of Jupiter

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PG Irwin

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