Publications by Fred Taylor

Oxygen compounds in Titan's stratosphere as observed by Cassini CIRS

Icarus 186 (2007) 354-363

FW Taylor, de Kok R, Irwin PGJ, Teanby NA

South-polar features on Venus similar to those near the north pole

Nature 450 (2007) 637-640

G Piccioni, P Drossart, A Sanchez-Lavega, R Hueso, FW Taylor, CF Wilson, D Grassi, L Zasova, M Moriconi, A Adriani, S Lebonnois, A Coradini, B Bézard, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, JP Bibring, A Blanco, MI Blecka, RW Carlson, A Di Lellis, T Encrenaz, S Erard, S Fonti, V Formisano, T Fouchet, R Garcia, R Haus, J Helbert, NI Ignatiev, PGJ Irwin, Y Langevin, MA Lopez-Valverde, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, DM Stam, D Titov, G Visconti, M Zambelli, E Ammannito, A Barbis, R Berlin, C Bettanini, A Boccaccini, G Bonnello, M Bouye, F Capaccioni, A Cardesin Moinelo, F Carraro, G Cherubini, M Cosi, M Dami, M De Nino, D Del Vento, M Di Giampietro, A Donati, O Dupuis, S Espinasse, A Fabbri, A Fave, IF Veltroni, G Filacchione, K Garceran, Y Ghomchi, M Giustini, B Gondet, Y Hello, F Henry, S Hofer, G Huntzinger, J Kachlicki, R Knoll, K Driss, A Mazzoni, R Melchiorri, G Mondello, F Monti, C Neumann, F Nuccilli, J Parisot, C Pasqui, S Perferi, G Peter, A Piacentino, C Pompei, JM Reess, JP Rivet, A Romano, N Russ, M Santoni, A Scarpelli, A Semery, A Soufflot

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. ©2007 Nature Publishing Group.

Scientific goals for the observation of Venus by VIRTIS on ESA/Venus express mission

Planetary and Space Science 55 (2007) 1653-1672

P Drossart, G Piccioni, A Adriani, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, B Bézard, JP Bibring, A Blanco, MI Blecka, RW Carlson, A Coradini, A Di Lellis, T Encrenaz, S Erard, S Fonti, V Formisano, T Fouchet, R Garcia, R Haus, J Helbert, NI Ignatiev, PGJ Irwin, Y Langevin, S Lebonnois, MA Lopez-Valverde, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, A Sanchez-Lavega, DM Stam, FW Taylor, D Titov, G Visconti, M Zambelli, R Hueso, CCC Tsang, CF Wilson, TZ Afanasenko

The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3-1 μm range), VIRTIS-M-IR (imaging spectrometer in the 1-5 μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2-5 μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H2O, OCS and SO2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 μm fundamental band of CO2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation. © 2007 Elsevier Ltd. All rights reserved.

Climate variability on Venus and Titan

SPACE SCIENCE REVIEWS 125 (2006) 445-455

FW Taylor

The composition of Titan's stratosphere from Cassini/CIRS mid-infrared spectra

Icarus 189 (2007) 35-62

A Coustenis, RK Achterberg, BJ Conrath, DE Jennings, A Marten, D Gautier, CA Nixon, FM Flasar, NA Teanby, B Bézard, RE Samuelson, RC Carlson, E Lellouch, GL Bjoraker, PN Romani, FW Taylor, PGJ Irwin, T Fouchet, A Hubert, GS Orton, VG Kunde, S Vinatier, J Mondellini, MM Abbas, R Courtin

We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006). The spectra characterize various regions on Titan from 70° S to 70° N with a variety of emission angles. We study the molecular signatures observed in the mid-infrared CIRS detector arrays (FP3 and FP4, covering roughly the 600-1500 cm-1 spectral range with apodized resolutions of 2.54 or 0.53 cm-1). The composite spectrum shows several molecular signatures: hydrocarbons, nitriles and CO2. A firm detection of benzene (C6H6) is provided by CIRS at levels of about 3.5 × 10-9 around 70° N. We have used temperature profiles retrieved from the inversion of the emission observed in the methane ν4 band at 1304 cm-1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere. No longitudinal variations were found for these gases. Little or no change is observed generally in their abundances from the south to the equator. On the other hand, meridional variations retrieved for these trace constituents from the equator to the North ranged from almost zero (no or very little meridional variations) for C2H2, C2H6, C3H8, C2H4 and CO2 to a significant enhancement at high northern (early winter) latitudes for HCN, HC3N, C4H2, C3H4 and C6H6. For the more important increases in the northern latitudes, the transition occurs roughly between 30 and 50 degrees north latitude, depending on the molecule. Note however that the very high-northern latitude results from tours TB-T10 bear large uncertainties due to few available data and problems with latitude smearing effects. The observed variations are consistent with some, but not all, of the predictions from dynamical-photochemical models. Constraints are set on the vertical distribution of C2H2, found to be compatible with 2-D equatorial predictions by global circulation models. The D/H ratio in the methane on Titan has been determined from the CH3D band at 1156 cm-1 and found to be 1.17-0.28+0.23 × 10-4. Implications of this deuterium enrichment, with respect to the protosolar abundance on the origin of Titan, are discussed. We compare our results with values retrieved by Voyager IRIS observations taken in 1980, as well as with more recent (1997) disk-averaged Infrared Space Observatory (ISO) results and with the latest Cassini-Huygens inferences from other instruments in an attempt to better comprehend the physical phenomena on Titan. © 2007 Elsevier Inc. All rights reserved.

Characterising Saturn's vertical temperature structure from Cassini/CIRS

Icarus 189 (2007) 457-478

LN Fletcher, PGJ Irwin, NA Teanby, GS Orton, PD Parrish, R de Kok, C Howett, SB Calcutt, N Bowles, FW Taylor

Thermal infrared spectra of Saturn from 10-1400 cm-1 at 15 cm-1 spectral resolution and a spatial resolution of 1°-2° latitude have been obtained by the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297]. Many thousands of spectra, acquired over eighteen-months of observations, are analysed using an optimal estimation retrieval code [Irwin, P.G.J., Parrish, P., Fouchet, T., Calcutt, S.B., Taylor, F.W., Simon-Miller, A.A., Nixon, C.A., 2004. Icarus 172, 37-49] to retrieve the temperature structure and para-hydrogen distribution over Saturn's northern (winter) and southern (summer) hemispheres. The vertical temperature structure is analysed in detail to study seasonal asymmetries in the tropopause height (65-90 mbar), the location of the radiative-convective boundary (350-500 mbar), and the variation with latitude of a temperature knee (between 150 and 300 mbar) which was first observed in inversions of Voyager/IRIS spectra [Hanel, R., and 15 colleagues, 1981. Science 212, 192-200; Hanel, R., Conrath, B., Flasar, F.M., Kunde, V., Maguire, W., Pearl, J.C., Pirraglia, J., Samuelson, R., Cruikshank, D.P., Gautier, D., Gierasch, P.J., Horn, L., Ponnamperuma, C., 1982. Science 215, 544-548]. Uncertainties due to both the modelling of spectral absorptions (collision-induced absorption coefficients, tropospheric hazes, helium abundance) and the nature of our retrieval algorithm are quantified. Temperatures in the stratosphere near 1 mbar show a 25-30 K temperature difference between the north pole and south pole. This asymmetry becomes less pronounced with depth as the radiative time constant for the atmospheric response increases at deeper pressure levels. Hemispherically-symmetric small-scale temperature structures associated with zonal winds are superimposed onto the temperature asymmetry for pressures greater than 100 mbar. The para-hydrogen fraction in the 100-400 mbar range is greater than equilibrium predictions for the southern hemisphere and parts of the northern hemisphere, and less than equilibrium predictions polewards of 40° N. The temperature knee between 150-300 mbar is larger in the summer hemisphere than in the winter, smaller and higher at the equator, deeper and larger in the equatorial belts and small at the poles. Solar heating on tropospheric haze is proposed as a possible mechanism for this effect; the increased efficiency of ortho- to para-hydrogen conversion in the southern hemisphere is consistent with the presence of larger aerosols in the summer hemisphere, which we demonstrate to be qualitatively consistent with previous studies of Saturn's tropospheric aerosol distribution. © 2007 Elsevier Inc. All rights reserved.

Vertical profiles of HCN, HC3N, and C2H2 in Titan's atmosphere derived from Cassini/CIRS data

Icarus 186 (2007) 364-384

NA Teanby, P.G.J. Irwin, R. de Kok, S. Vinatier

The 2003 November 14 occultation by Titan of TYC 1343-1865-1. II. Analysis of light curves

Icarus 192 (2007) 503-518

A Zalucha, A Fitzsimmons, JL Elliot, J Thomas-Osip, HB Hammel, VS Dhillon, TR Marsh, FW Taylor, PGJ Irwin

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u′, g′, and i′ (358, 487, and 758 nm, respectively). The occultation probed latitudes 2° S and 1° N during immersion and emersion, respectively. A prominent central flash was present in only the i′ filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i′ profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396 ± 7 and 401 ± 20  km (u′ immersion and emersion); 354 ± 7 and 387 ± 7  km (g′ immersion and emersion); and 336 ± 5 and 318 ± 4  km (i′ immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3 ± 0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541-563]. © 2007 Elsevier Inc. All rights reserved.

A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express

NATURE 450 (2007) 641-645

P Drossart, G Piccioni, JC Gerard, MA Lopez-Valverde, A Sanchez-Lavega, L Zasova, R Hueso, FW Taylor, B Bezard, A Adriani, F Angrilli, G Arnold, KH Baines, G Bellucci, J Benkhoff, JP Bibring, A Blanco, MI Blecka, RW Carlson, A Coradini, A Di Lellis, T Encrenaz, S Erard, S Fonti, V Formisano, T Fouchet, R Garcia, R Haus, J Helbert, NI Ignatiev, P Irwin, Y Langevin, S Lebonnois, D Luz, L Marinangeli, V Orofino, AV Rodin, MC Roos-Serote, B Saggin, DM Stam, D Titov, G Visconti, M Zambelli, C Tsang, V-VET Te

The meridional phosphine distribution in Saturn's upper troposphere from Cassini/CIRS observations

Icarus 188 (2007) 72-88

LN Fletcher, PGJ Irwin, NA Teanby, GS Orton, PD Parrish, SB Calcutt, N Bowles, R de Kok, C Howett, FW Taylor

The Cassini Composite Infrared Spectrometer (CIRS) has been used to derive the vertical and meridional variation of temperature and phosphine (PH3) abundance in Saturn's upper troposphere. PH3 has a significant effect on the measured radiances in the thermal infrared and between May 2004 and September 2005 CIRS recorded thousands of spectra in both the far (10-600 cm-1) and mid (600-1400 cm-1) infrared, at a variety of latitudes covering the southern hemisphere. Low spectral resolution (15 cm-1) data has been used to constrain the temperature structure of the troposphere between 100 and 500 mbar. The vertical distributions of phosphine and ammonia were retrieved from far-infrared spectra at the highest spectral resolution (0.5 cm-1), and lower resolution (2.5 cm-1) mid-infrared data were used to map the meridional variation in the abundance of phosphine in the 250-500 mbar range. Temperature variations at the 250 mbar level are shown to occur on the same scale as the prograde and retrograde jets in Saturn's atmosphere [Porco, C.C., and 34 colleagues, 2005. Science 307, 1243-1247]. The PH3 abundance at 250 mbar is found to be enhanced at the equator when compared with mid-latitudes. At mid latitudes we see anti-correlation between temperature and PH3 abundance at 250 mbar, phosphine being enhanced at 45° S and depleted at 25 and 55° S. The vertical distribution is markedly different polewards of 60-65° S, with depleted PH3 at 500 mbar but a slower decline in abundance with altitude when compared with the mid-latitudes. This variation is similar to the variations of cloud and aerosol parameters observed in the visible and near infrared, and may indicate the subsidence of tropospheric air at polar latitudes, coupled with a diminished sunlight penetration depth reducing the rate of PH3 photolysis in the polar region. © 2006 Elsevier Inc. All rights reserved.

Planetary and, space science - Preface - Introduction to the Venus express special issue, vol. 2


FW Taylor

The composition of the atmosphere of Venus below 100 km altitude: An overview


C de Bergh, VI Moroz, FW Taylor, D Crisp, B Bezard, LV Zasova

Latitudinal variations of HCN, HC3N, and C2N2 in Titan's stratosphere derived from cassini CIRS data

Icarus 181 (2006) 243-255

NA Teanby, PGJ Irwin, R de Kok, CA Nixon

Introduction to the Venus Express special issue


FW Taylor

Venus before Venus express


FW Taylor

Concepts for a low-cost Mars micro mission

ACTA ASTRONAUT 59 (2006) 617-626

RJ Walker, AJ Ball, ME Price, MR Sims, FW Taylor, NS Wells, JC Zarnecki

This paper summarises three novel micro-mission concepts for the low-cost exploration of the Martian system. These concepts have been studied under national funding with the aim of defining highly cost-effective options for the delivery of on-board instrumentation into Mars orbit for remote sensing or deployment of lander packages for surface exploration of the Martian system. All three missions use advanced electric propulsion to improve payload mass performance and miniaturised avionics either in the spacecraft bus or payload. Broadly, the three concepts are categorised according to mass: a constellation of micro-satellites (120kg) in low Mars polar orbit for global atmospheric circulation/climate monitoring using radio occultation techniques; a single mini-satellite (310kg) for studying composition and origins of Mars' moons Deimos and Phobos; and a single larger spacecraft (800kg) based on a standard launcher adapter cone and carrying multiple micro-penetrators for measuring sub-surface water ice composition at pre-determined locations on the surface of Mars. (c) 2005 Elsevier Ltd. All rights reserved.

Atmospheric temperature sounding on Mars, and the climate sounder on the 2005 reconnaissance orbiter

ADV SPACE RES 38 (2006) 713-717

FW Taylor, SB Calcutt, PL Read, SR Lewis, DJ McCleese, JT Schofield, RW Zurek

Detailed measurements of the vertical profiles of atmospheric temperature, water vapour, dust and condensates in the Martian atmosphere are needed to characterize the present-day Martian climate and to understand the intricately related processes upon which it depends. Among the most important of these are accurate and extensive temperature measurements. Progress to date, key problems still to be addressed and upcoming new approaches to the measurement task are briefly reviewed, and expectations for the Mars Climate Sounder experiment on the 2005 Mars Reconnaissance Orbiter are described. Some even more advanced methods for temperature, humidity and condensate sounding in the decade beyond MCS/MRO, and promising approaches to achieving these are also considered. (c) 2006 Published by Elsevier Ltd on behalf of COSPAR.

Atmospheric temperature sounding on Mars, and the climate sounder on the 2005 reconnaissance orbiter


FW Taylor, SB Calcutt, PL Read, SR Lewis, DJ McCleese, JT Schofield, RW Zurek

Venus Express: Scientific goals, instrumentation, and scenario of the mission

Cosmic Research 44 (2006) 334-348

DV Titov, H Svedhem, D McCoy, JP Lebreton, S Barabash, JL Bertaux, P Drossart, V Formisano, B Haeusler, OI Korablev, W Markiewicz, D Neveance, M Petzold, G Piccioni, TL Zhang, FW Taylor, E Lellouch, D Koschny, O Witasse, M Warhaut, A Acomazzo, J Rodrigues-Cannabal, J Fabrega, T Schirmann, A Clochet, M Coradini

The first European mission to Venus (Venus Express) is described. It is based on a repeated use of the Mars Express design with minor modifications dictated in the main by more severe thermal environment at Venus. The main scientific task of the mission is global exploration of the Venusian atmosphere, circumplanetary plasma, and the planet surface from an orbiting spacecraft. The Venus Express payload includes seven instruments, five of which are inherited from the missions Mars Express and Rosetta. Two instruments were specially designed for Venus Express. The advantages of Venus Express in comparison with previous missions are in using advanced instrumentation and methods of remote sounding, as well as a spacecraft with a broad spectrum of capabilities of orbital observations. © Pleiades Publishing, Inc., 2006.

Comparative Planetary Climatology

SURVEYS IN GEOPHYSICS 27 (2006) 149-167

FW Taylor