Publications


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.


Jupiter's auroral-related stratospheric heating and chemistry II: Analysis of IRTF-TEXES spectra measured in December 2014

ICARUS 300 (2018) 305-326

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


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

ICARUS 302 (2018) 426-436

PGJ Irwin, N Bowles, AS Braude, R Garland, S Calcutt


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

ASTRONOMY & ASTROPHYSICS 609 (2018) ARTN A64

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


Jupiter's North Equatorial Belt expansion and thermal wave activity ahead of Juno's arrival

GEOPHYSICAL RESEARCH LETTERS 44 (2017) 7140-7148

LN Fletcher, GS Orton, JA Sinclair, P Donnelly, H Melin, JH Rogers, TK Greathouse, Y Kasaba, T Fujiyoshi, TM Sato, J Fernandes, PGJ Irwin, RS Giles, AA Simon, MH Wong, M Vedovato


A precise optical transmission spectrum of the inflated exoplanet WASP-52b

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 470 (2017) 742-754

T Louden, PJ Wheatley, PGJ Irwin, J Kirk, I Skillen


CASTAway: An asteroid main belt tour and survey

Advances in Space Research (2017)

NE Bowles, C Snodgrass, A Gibbings, JP Sanchez, JA Arnold, P Eccleston, T Andert, A Probst, G Naletto, AC Vandaele, J de Leon, A Nathues, IR Thomas, N Thomas, L Jorda, V Da Deppo, H Haack, SF Green, B Carry, KL Donaldson Hanna, J Leif Jorgensen, A Kereszturi, FE DeMeo, MR Patel, JK Davies, F Clarke, K Kinch, A Guilbert-Lepoutre, J Agarwal, AS Rivkin, P Pravec, S Fornasier, M Granvik, RH Jones, N Murdoch, KH Joy, E Pascale, M Tecza, JM Barnes, J Licandro, BT Greenhagen, SB Calcutt, CM Marriner, T Warren, I Tosh

© 2017 COSPAR. CASTAway is a mission concept to explore our Solar System's main asteroid belt. Asteroids and comets provide a window into the formation and evolution of our Solar System and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. Variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the Solar System. The mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10-20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. With a carefully targeted trajectory that loops through the asteroid belt, CASTAway would provide a comprehensive survey of the main belt at multiple scales. The scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (R = 30-100) spectrometer and visible context imager, a thermal (e.g. 6-16 μm) imager for use during the flybys, and modified star tracker cameras to detect small ( 10 m) asteroids. The CASTAway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a European Space Agency medium class mission, while delivering a significant increase in knowledge of our Solar System.


Ammonia in Jupiter's Troposphere From High-Resolution 5 mu m Spectroscopy

GEOPHYSICAL RESEARCH LETTERS 44 (2017) 10838-10844

RS Giles, LN Fletcher, PGJ Irwin, GS Orton, JA Sinclair


D/H Ratios on Saturn and Jupiter from Cassini CIRS

ASTRONOMICAL JOURNAL 154 (2017) ARTN 178

JDR Pierel, CA Nixon, E Lellouch, LN Fletcher, GL Bjoraker, RK Achterberg, B Bezard, BE Hesman, PGJ Irwin, FM Flasar


Space weathering effects in Diviner Lunar Radiometer multispectral infrared measurements of the lunar Christiansen Feature: Characteristics and mitigation

ICARUS 283 (2017) 343-351

PG Lucey, BT Greenhagen, E Song, JA Arnold, M Lemelin, KD Hanna, NE Bowles, TD Glotch, DA Paige


Latitudinal variability in Jupiter ' s tropospheric disequilibrium species: GeH4, AsH3 and PH3

ICARUS 289 (2017) 254-269

RS Giles, LN Fletcher, PGJ Irwin


Regimes of Axisymmetric Flow and Scaling Laws in a Rotating Annulus with Local Convective Forcing

Fluids 2 (2017) 41-41

S Wright, S Su, H Scolan, R Young, P Read


Mapping Vinyl Cyanide and Other Nitriles in Titan's Atmosphere Using ALMA

ASTRONOMICAL JOURNAL 154 (2017) ARTN 206

JC-Y Lai, MA Cordiner, CA Nixon, RK Achterberg, EM Molter, NA Teanby, MY Palmer, SB Chamley, JE Lindberg, Z Kisiel, MJ Mumma, PGJ Irwin


The PanCam Instrument for the ExoMars Rover

ASTROBIOLOGY 17 (2017) 511-541

AJ Coates, R Jaumann, AD Griffiths, CE Leff, N Schmitz, J-L Josset, G Paar, M Gunn, E Hauber, CR Cousins, RE Cross, P Grindrod, JC Bridges, M Balme, S Gupta, IA Crawford, P Irwin, R Stabbins, D Tirsch, JL Vago, T Theodorou, M Caballo-Perucha, GR Osinski, P Team


Linking the Climate and Thermal Phase Curve of 55 Cancri e

Astrophysical Journal 849 (2017)

M Hammond, RT Pierrehumbert

© 2017. The American Astronomical Society. All rights reserved. The thermal phase curve of 55 Cancri e is the first measurement of the temperature distribution of a tidally locked super-Earth, but raises a number of puzzling questions about the planet's climate. The phase curve has a high amplitude and peak offset, suggesting that it has a significant eastward hot-spot shift as well as a large day-night temperature contrast. We use a general circulation model to model potential climates, and investigate the relation between bulk atmospheric composition and the magnitude of these seemingly contradictory features. We confirm theoretical models of tidally locked circulation are consistent with our numerical model of 55 Cnc e, and rule out certain atmospheric compositions based on their thermodynamic properties. Our best-fitting atmosphere has a significant hot-spot shift and day-night contrast, although these are not as large as the observed phase curve. We discuss possible physical processes that could explain the observations, and show that night-side cloud formation from species such as SiO from a day-side magma ocean could potentially increase the phase curve amplitude and explain the observations. We conclude that the observations could be explained by an optically thick atmosphere with a low mean molecular weight, a surface pressure of several bars, and a strong eastward circulation, with night-side cloud formation a possible explanation for the difference between our model and the observations.


Independent evolution of stratospheric temperatures in Jupiter's northern and southern auroral regions from 2014 to 2016

GEOPHYSICAL RESEARCH LETTERS 44 (2017) 5345-5354

JA Sinclair, GS Orton, TK Greathouse, LN Fletcher, C Tao, GR Gladstone, A Adriani, W Dunn, JI Moses, V Hue, PGJ Irwin, H Melin, RS Giles


ALMA detection and astrobiological potential of vinyl cyanide on Titan.

Science advances 3 (2017) e1700022-

MY Palmer, MA Cordiner, CA Nixon, SB Charnley, NA Teanby, Z Kisiel, PGJ Irwin, MJ Mumma

Recent simulations have indicated that vinyl cyanide is the best candidate molecule for the formation of cell membranes/vesicle structures in Titan's hydrocarbon-rich lakes and seas. Although the existence of vinyl cyanide (C2H3CN) on Titan was previously inferred using Cassini mass spectrometry, a definitive detection has been lacking until now. We report the first spectroscopic detection of vinyl cyanide in Titan's atmosphere, obtained using archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), collected from February to May 2014. We detect the three strongest rotational lines of C2H3CN in the frequency range of 230 to 232 GHz, each with >4σ confidence. Radiative transfer modeling suggests that most of the C2H3CN emission originates at altitudes of ≳200 km, in agreement with recent photochemical models. The vertical column densities implied by our best-fitting models lie in the range of 3.7 × 1013 to 1.4 × 1014 cm-2. The corresponding production rate of vinyl cyanide and its saturation mole fraction imply the availability of sufficient dissolved material to form ~107 cell membranes/cm3 in Titan's sea Ligeia Mare.


An experimental investigation of blocking by partial barriers in a rotating baroclinic annulus

Geophysical and Astrophysical Fluid Dynamics (2017) 1-33

SD Marshall, PL Read

© 2017 Informa UK Limited, trading as Taylor & Francis Group We present a series of experimental investigations in which a differentially-heated annulus was used to investigate the effects of topography on rotating, stratified flows with similarities to the Earth’s atmospheric or oceanic circulation. In particular, we compare and investigate blocking effects via partial mechanical barriers to previous experiments by the authors utilising azimuthally-periodic topography. The mechanical obstacle used was an isolated ridge, forming a partial barrier, employed to study the difference between partially blocked and fully unblocked flow. The topography was found to lead to the formation of bottom-trapped waves, as well as impacting the circulation at a level much higher than the top of the ridge. This produced a unique flow structure when the drifting flow and the topography interacted in the form of an “interference” regime at low Taylor number, but forming an erratic “irregular” regime at higher Taylor number. The results also showed evidence of resonant wave-triads, similar to those noted with periodic wavenumber-3 topography by Marshall and Read (Geophys. Astrophys. Fluid Dyn., 2015, 109), though the component wavenumbers of the wave-triads and their impact on the flow were found to depend on the topography in question. With periodic topography, wave-triads were found to occur between both the baroclinic and barotropic components of the zonal wavenumber-3 mode and the wavenumber-6 baroclinic component, whereas with the partial barrier two nonlinear resonant wave-triads were noted, each sharing a common wavenumber-1 mode.


A CONSISTENT RETRIEVAL ANALYSIS OF 10 HOT JUPITERS OBSERVED IN TRANSMISSION

ASTROPHYSICAL JOURNAL 834 (2017) ARTN 50

JK Barstow, S Aigrain, PGJ Irwin, DK Sing


Rayleigh scattering in the transmission spectrum of HAT-P-18b

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 468 (2017) 3907-3916

J Kirk, PJ Wheatley, T Louden, AP Doyle, I Skillen, J McCormac, PGJ Irwin, R Karjalainen

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