Publications by Patrick Irwin

Search for spatial variation in the jovian 15N/14N ratio from Cassini/CIRS observations

Icarus 172 (2004) 50-58

SB Calcutt, Fouchet, Irwin, Parrish

Upper limits on hydrogen halides in Jupiter from Cassini/CIRS observations

Icarus 170 (2004) 237-241

T Fouchet, G Orton, PGJ Irwin, SB Calcutt, CA Nixon

We have determined the following upper limits for the mole fraction of hydrogen halides in Jupiter's atmosphere from Cassini/CIRS observations: [HF] <2.7×10-11, [HCl] <2.3×10-9, [HBr]<1.0×10-9, [HI] <7.6×10-9. These limits are smaller than solar composition for HF and HCl, and support the halogens' condensation in ammonium salts predicted by thermochemical models for the upper jovian troposphere. © 2004 Published by Elsevier Inc.

Jupiter's atmospheric composition from the Cassini thermal infrared spectroscopy experiment.

Science 305 (2004) 1582-1586

VG Kunde, FM Flasar, DE Jennings, B Bézard, DF Strobel, BJ Conrath, CA Nixon, GL Bjoraker, PN Romani, RK Achterberg, AA Simon-Miller, P Irwin, JC Brasunas, JC Pearl, MD Smith, GS Orton, PJ Gierasch, LJ Spilker, RC Carlson, AA Mamoutkine, SB Calcutt, PL Read, FW Taylor, T Fouchet, P Parrish, A Barucci, R Courtin, A Coustenis, D Gautier, E Lellouch, A Marten, R Prangé, Y Biraud, C Ferrari, TC Owen, MM Abbas, RE Samuelson, F Raulin, P Ade, CJ Césarsky, KU Grossman, A Coradini

The Composite Infrared Spectrometer observed Jupiter in the thermal infrared during the swing-by of the Cassini spacecraft. Results include the detection of two new stratospheric species, the methyl radical and diacetylene, gaseous species present in the north and south auroral infrared hot spots; determination of the variations with latitude of acetylene and ethane, the latter a tracer of atmospheric motion; observations of unexpected spatial distributions of carbon dioxide and hydrogen cyanide, both considered to be products of comet Shoemaker-Levy 9 impacts; characterization of the morphology of the auroral infrared hot spot acetylene emission; and a new evaluation of the energetics of the northern auroral infrared hot spot.

An intense stratospheric jet on Jupiter

Nature 427 (2004) 132-135

SB Calcutt, Achtergerg, Flasar, Kunde

Retrievals of Jovian tropospheric phosphine from Cassini/CIRS

Icarus 172 (2004) 37-49

PG Irwin, P. Parrish, T. Fouchet, S. B. Calcutt

Feasibility study of a stratospheric-airship observatory

Proceedings of SPIE - The International Society for Optical Engineering 4857 (2002) 227-238

D Griffin, B Swinyard, S Sidher, P Irwin

This paper explores the concept of utilizing a long duration stratospheric airship as an astronomical observatory in the sub-millimetre wavelengths. In the first section of the paper, a conceptual description of the airship platform is presented along with the principles of operation of the platform. The results of a computer design code and trajectory simulation code are presented. These codes show that through the use of a modest power and propulsion system, the difficulty of constructing such a such a platform is greatly reduced. Finally, the results of a brief study into the accommodation and optical performance of a Ø3.5m class telescope and photometric and spectrographic instrument similar to the Herschel/SPIRE system within such an airship are presented. This study indicates that while the atmospheric absorption and emission characteristics impose some limitations on the spectrographic and photometric performance of the system in the 200μm to 1000μm band, the overall performance is more than adequate to render the concept viable and complementary to existing and planned ground, airborne and space based observatories.

Correlation of near-infrared albedo and 5-micron brightness variations in Jupiter's atmosphere

ADV SPACE RES 29 (2002) 285-290

PGJ Irwin, SB Calcutt, AL Weir, FW Taylor, RW Carlson

The Galileo Near Infrared Mapping Spectrometer (NIMS) has returned many spectra of the Jovian atmosphere in the range 0.7-5.2 mum. Although communications restrictions have limited the data return, several wide-area maps have been recorded at near full NIMS resolution. Using these data it is possible to determine both the average shape of the near-infrared (NIR) spectra with very thick clouds (and zero 5-mum brightness) and how these spectra vary as the 5-mum brightness increases.In most of the cases studied, we find that the variable part of the reflectivity has a very different shape to the mean part and may best be explained by variable reflectivity in the cloud layers at pressures greater than 1 bar. In these cases it would thus appear that a variable opacity in a cloud deck based between 1 and 2 bars is mainly responsible for the NIR albedo variations, and not a higher ammonia cloud based above 1 bar as has often been previously suggested. While the composition of this main variable cloud deck could well be ammonium hydrosulphide, other candidates include ammonia (should the much higher estimate of its deep gaseous fractional abundance resulting from the Galileo probe mission be correct), and perhaps even the upper reaches of a deeper water cloud. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

The retrieval of cloud structure maps in the Equatorial region of Jupiter using a principal component analysis of Galileo/NIMS data

Icarus 156 (2002) 52-63

PG Irwin, U. Dyudina

Atmospheric composition and cloud structure in jovian 5-μm hotspots from analysis of Galileo NIMS measurements

Icarus 150 (2001) 48-68

CA Nixon, PGJ Irwin, SB Calcutt, FW Taylor, RW Carlson

NIMS is the Near-Infrared Mapping Spectrometer on board the Galileo spacecraft in jovian orbit. We have selected four maps of warm-to-hot regions of the North Equatorial Belt (NEB) for study, analyzing the spectra emerging in the low-opacity 5-μm window. Two methods for calculating the spectrum have been used. The first is a full-scattering radiative transfer forward model that is slow but accurate. The second method calculates spectra by interpolating on a grid of spectra precalculated using the first method for a range of model atmospheres. This method of forward calculation is more suited to analysis of large data sets where application of the full radiative transfer in every instance would be computationally prohibitive. The faster method is verified against the first before being used alone. A retrieval (inversion) algorithm is then used to match model spectra to data and obtain values for cloud opacities and gas mixing ratios. We first sum spectra with similar peak radiances to produce mean spectra representative of brighter and darker (at 5 μm) regions of the maps. These coadded spectra are then analyzed with the fast retrieval code to obtain the average variations in atmospheric parameters from the center to the edges of the hotspots. These analyses confirm that 5-μm hotspots are relatively cloud free, and that a medium level (1.5-bar) cloud layer of large NH4SH particles is the main absorber at these wavelengths. Variations in water vapor relative humidity and high (0.5-bar) ammonia cloud opacity are also derived. We then analyze single spectra over wide areas to produce spatial maps of parameter variations. We find that models that do not include a deep water cloud (~4 bar) do not match all the spectra to within the noise level. A deep water cloud therefore seems to be present in localized areas, toward the edges of the hotspot regions. We examine these findings in the light of results from other Galileo instruments, concluding that the deep cloud observed by the SSI instrument at several locations is likely to be the deep water cloud required by the NIMS data. © 2001 Academic Press.

The origin of belt/zone contrasts in the atmosphere of Jupiter and their correlation with 5-micron opacity

Icarus 149 (2001) 397-415

PG Irwin, A.L. Weir, F.W. Taylor, S.B. Calcutt

The origin of belt/zone contrasts in the atmosphere of Jupiter and their correlation with 5-mu m opacity

ICARUS 149 (2001) 397-415

PGJ Irwin, AL Weir, FW Taylor, SB Calcutt, RW Carlson

Proximate humid and dry regions in Jupiter's atmosphere indicate complex local meteorology

Nature 405 (2000) 158-160

M Roos-Serote, AR Vasavada, L Kamp, P Drossart, P Irwin, C Nixon, RW Carlson

Models of Jupiter's formation and structure predict that its atmosphere is enriched in oxygen, relative to the Sun, and that consequently water clouds should be present globally near the 5-bar pressure level. Past attempts to confirm these predictions have led to contradictory results; in particular, the Galileo probe revealed a very dry atmosphere at the entry site, with no significant clouds at depths exceeding the 2-bar level. Although the entry site was known to be relatively cloud-free, the contrast between the observed local dryness and the expected global wetness was surprising. Here we analyse near-infrared (around 5 μm) observations of Jupiter, a spectral region that can reveal the water vapour abundance and vertical cloud structure in the troposphere. We find that humid and extremely dry regions exist in close proximity, and that some humid regions are spatially correlated with bright convective clouds extending from the deep water clouds to the visible atmosphere.

The clouds of Jupiter

ASTRONOMY & GEOPHYSICS 40 (1999) 21-25

F Taylor, P Irwin

Jovian atmospheric studies with the Galileo near infrared mapping spectrometer: An update

ADV SPACE RES 23 (1999) 1623-1632

PGJ Irwin, FW Taylor, RW Carlson, KH Baines, A Weir, P Cameron-Smith, S Calcutt, T Encrenaz, P Drossart, M Roos-Serote, E Lellouch

In its first two years of operation since arrival at Jupiter in December 1995, the Near Infrared Mapping spectrometer (NIMS) on the Galileo orbiter spacecraft obtained extensive coverage of the planet, including detailed coverage of the north equatorial belt (NEB) 'hot spot' region and the Great Red Spot. We will present the current state of data analysis including recent results on the abundances and variability of several minor constituents (H2O, CH4, NH3, GeH4, CH3D and PH3) and the cloud structure and morphology. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Band parameters and k coefficients for self-broadened ammonia in the range 4000-11000 cm(-1)


PGJ Irwin, SB Calcutt, K Sihra, FW Taylor, AL Weir, J Ballard, WB Johnston

The clouds of Jupiter

Astronomy and Geophysics 40 (1999) 321-325

F Taylor, P Irwin

The highly organized and brightly coloured cloud structure on the nearest and largest gas giant planet Jupiter has been explored by the Galileo orbiter/probe project, which completed its nominal mission in December 1997. At least four and possibly as many as six distinct layers of haze or cloud, of different composition and at different depths, appear to contribute to the external appearance of the planet at low and mid-latitudes. A model of the properties of these clouds has been developed from the various data and theoretical constrains. Aspects of the global and time variability of the cloud structure, and its coupling with dynamical systems like the Great Red Spot, are also becoming clearer, allowing speculation about their nature and origins. Analyses of the full four-year data set, some of which is still to be acquired, will add further details of the meteorological behaviour of Jupiter's atmosphere.

Cloud structure and composition of Jupiter's atmosphere

Surveys in Geophysics 20 (1999) 505-535

PGJ Irwin

The understanding of the composition and cloud structure has advanced greatly in the last few years and in particular was greatly improved upon following the highly successful Pioneer and Voyager missions to that planet. Recently the Galileo spacecraft has gone into orbit about Jupiter and its remote sensing instruments, including the Near Infrared Mapping Spectrometer (NIMS) and the Solid State Imager (SSI), have yielded exciting new details of the spatial and vertical structure of the Jovian clouds and volatiles. At the same time Galileo's entry probe has made the first ever in situ measurements of conditions in the atmosphere. Recent ground-based observations have also added to the body of evidence from which conditions in the Jovian atmosphere may be inferred. This paper aims to review the current understanding of the composition and cloud structure of Jupiter's atmosphere in the light of the new Galileo results and recent ground-based, and earth-orbiting telescope observations.

The atmosphere of Mars

JBIS - Journal of the British Interplanetary Society 52 (1999) 209-216

PGJ Irwin, SB Calcutt, FW Taylor, DJ McCleese

Mars, one of the most Earth-like of the planets, is today a cold, dry and barren world. However, there is good evidence that it may have been much warmer and wetter in the past and perhaps even supported life. The public interest aroused by these findings and by recent studies of 'SNC' meteorites, believed to have come from Mars, with their claims of the evidence of ancient Martian life, has focused attention on the ambitious programme of Mars Exploration currently being undertaken by NASA and ESA and has provided additional impetus. Improved measurements of the conditions on Mars' surface and in its atmosphere are central to both agencies' plans, and current atmospheric missions are reviewed in this paper together with possible future designs.

VIRTIS: an imaging spectrometer for the ROSETTA mission


A Coradini, F Capaccioni, P Drossart, A Semery, G Arnold, U Schade, F Angrilli, MA Barucci, G Bellucci, G Bianchini, JP Bibring, A Blanco, M Blecka, D Bockelee-Morvan, R Bonsignori, M Bouye, E Bussoletti, MT Capria, R Carlson, U Carsenty, P Cerroni, L Colangeli, M Combes, M Combi, J Crovisier, M Dami, MC DeSanctis, AM DiLellis, E Dotto, T Encrenaz, E Epifani, S Erard, S Espinasse, A Fave, C Federico, U Fink, S Fonti, V Formisano, Y Hello, H Hirsch, G Huntzinger, R Knoll, D Kouach, WH Ip, P Irwin, J Kachlicki, Y Langevin, G Magni, T McCord, V Mennella, H Michaelis, G Mondello, S Mottola, G Neukum, V Orofino, R Orosei, P Palumbo, G Peter, B Pforte, G Piccioni, JM Reess, E Ress, B Saggin, B Schmitt, D Stefanovitch, A Stern, F Taylor, D Tiphene, G Tozzi

Investigation of Saturn's atmosphere by Cassini

PLANET SPACE SCI 46 (1998) 1315-1324

FW Taylor, SB Calcutt, PGJ Irwin, CA Nixon, PL Read, PJC Smith, TJ Vellacott

This paper considers the rationale for the exploration of Saturn's atmosphere by the Cassini mission, taking account of the key scientific questions posed by the earlier investigation by Voyager, and the capabilities of the instrumentation making up the Cassini payload. While by no means all objectives can be addressed by this particular configuration, in particular without a Saturn entry probe, if everything goes according to plan important progress should be possible on a number of key objectives. (C) 1998 Elsevier Science Ltd. All rights reserved.