Publications by Neil Bowles

ORTIS - ORbiter terahertz infrared sounder

21st International Symposium on Space Terahertz Technology 2010, ISSTT 2010 (2010) 208-

BN Ellison, PGJ Irwin, SB Calcutt, S Rea, B Alderman, N Bowles, R Irshad, J Hurley

Accurate measurement of the temperature, composition and dynamics of Jupiter's atmosphere is one of the main scientific goals of ESA's and NASA's Outer Planet Mission proposals. Infrared remote sounding provides a powerful tool for achieving these objectives and was used by Voyager/IRIS and Cassini/CIRS, but is insensitive to some altitudes and gases. The sub-millimetre wavelength (terahertz) region of the electromagnetic spectrum, which has not been significantly exploited to date in the discipline of planetary science, provides unique spectral information over a range of atmospheric pressures and, when combined with infrared data, is a powerful in situ planetary atmospheric sounder. We will describe a novel low mass and low power consumption combined terahertz/IR instrument proposed for inclusion on the Jupiter Ganymede Orbiter that will greatly improve our understanding of the atmosphere of Jupiter. Through the combination of high spectral resolution 2.2THz spectroscopy (R=10<sup>6</sup>) and lowspectral resolution IR radiometry, the entire temperature profile of the Jovian atmosphere from 0.6 to 10<sup>-3</sup> bar can be evaluated (filling in the currently unmeasured levels between 0.1 and 0.01 bar). In addition, the tropospheric and stratospheric composition can be determined (especially water vapour) and observations of the Doppler shifting of sub-millimetre lines can also be used to measure horizontal wind speeds.

HARMONI: a single-field, wide-band, integral field spectrograph for the European ELT


N Thatte, M Tecza, F Clarke, RL Davies, A Remillieux, R Bacon, D Lunney, S Arribas, E Mediavilla, F Gago, N Bezawada, P Ferruit, A Fragoso, D Freeman, J Fuentes, T Fusco, A Gallie, A Garcia, T Goodsall, F Gracia, A Jarno, J Kosmalski, J Lynn, S McLay, D Montgomery, A Pecontal, H Schnetler, H Smith, D Sosa, G Battaglia, N Bowles, L Colina, E Emsellem, A Garcia-Perez, S Gladysz, I Hook, P Irwin, M Jarvis, R Kennicutt, A Levan, A Longmore, J Magorrian, M McCaughrean, L Origlia, R Rebolo, D Rigopoulou, S Ryan, M Swinbank, N Tanvir, E Tolstoy, A Verma

Diviner lunar radiometer observations of cold traps in the moon's south polar region

Science 330 (2010) 479-482

DA Paige, MA Siegler, JA Zhang, PO Hayne, EJ Foote, KA Bennett, AR Vasavada, BT Greenhagen, JT Schofield, DJ McCleese, MC Foote, E DeJong, BG Bills, W Hartford, BC Murray, CC Allen, K Snook, LA Soderblom, S Calcutt, FW Taylor, NE Bowles, JL Bandfield, R Elphic, R Ghent, TD Glotch, MB Wyatt, PG Lucey

Diviner Lunar Radiometer Experiment surface-temperature maps reveal the existence of widespread surface and near-surface cryogenic regions that extend beyond the boundaries of persistent shadow. The Lunar Crater Observation and Sensing Satellite (LCROSS) struck one of the coldest of these regions, where subsurface temperatures are estimated to be 38 kelvin. Large areas of the lunar polar regions are currently cold enough to cold-trap water ice as well as a range of both more volatile and less volatile species. The diverse mixture of water and high-volatility compounds detected in the LCROSS ejecta plume is strong evidence for the impact delivery and cold-trapping of volatiles derived from primitive outer solar system bodies.

Global silicate mineralogy of the moon from the diviner lunar radiometer

Science 329 (2010) 1507-1509

BT Greenhagen, PG Lucey, MB Wyatt, TD Glotch, CC Allen, JA Arnold, JL Bandfield, NE Bowles, KLD Hanna, PO Hayne, E Song, IR Thomas, DA Paige

We obtained direct global measurements of the lunar surface using multispectral thermal emission mapping with the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment. Most lunar terrains have spectral signatures that are consistent with known lunar anorthosite and basalt compositions. However, the data have also revealed the presence of highly evolved, silica-rich lunar soils in kilometer-scale and larger exposures, expanded the compositional range of the anorthosites that dominate the lunar crust, and shown that pristine lunar mantle is not exposed at the lunar surface at the kilometer scale. Together, these observations provide compelling evidence that the Moon is a complex body that has experienced a diverse set of igneous processes.

Highly silicic compositions on the moon

Science 329 (2010) 1510-1513

TD Glotch, PG Lucey, JL Bandfield, BT Greenhagen, IR Thomas, RC Elphic, N Bowles, MB Wyatt, CC Allen, KD Hanna, DA Paige

Using data from the Diviner Lunar Radiometer Experiment, we show that four regions of the Moon previously described as "red spots" exhibit mid-infrared spectra best explained by quartz, silica-rich glass, or alkali feldspar. These lithologies are consistent with evolved rocks similar to lunar granites in the Apollo samples. The spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar. The variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the Moon. Basaltic underplating is the preferred mechanism for silicic magma generation, leading to the formation of extrusive landforms. This mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies.

Global Silicate Mineralogy of the Moon from the Diviner Lunar Radiometer

SCIENCE 329 (2010) 1507-1509

BT Greenhagen, PG Lucey, MB Wyatt, TD Glotch, CC Allen, JA Arnold, JL Bandfield, NE Bowles, KLD Hanna, PO Hayne, E Song, IR Thomas, DA Paige

The future of planetary geophysics

Astronomy and Geophysics 51 (2010) 2.22-2.25

N Teanby, N Bowles

M. eeting report Nick Teanby and Neil Bowles look to the future for planetary geophysics, drawing together ideas discussed at an RAS Discussion Meeting in November. © 2010 Royal Astronomical Society.

The Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment

SPACE SCIENCE REVIEWS 150 (2010) 125-160

DA Paige, MC Foote, BT Greenhagen, JT Schofield, S Calcutt, AR Vasavada, DJ Preston, FW Taylor, CC Allen, KJ Snook, BM Jakosky, BC Murray, LA Soderblom, B Jau, S Loring, J Bulharowski, NE Bowles, IR Thomas, MT Sullivan, C Avis, EM De Jong, W Hartford, DJ McCleese

The lunar reconnaissance orbiter diviner lunar radiometer experiment

Space Science Reviews 150 (2010) 125-160

DA Paige, MC Foote, BT Greenhagen, JT Schofield, S Calcutt, AR Vasavada, DJ Preston, FW Taylor, CC Allen, KJ Snook, BM Jakosky, BC Murray, LA Soderblom, B Jau, S Loring, J Bulharowski, NE Bowles, IR Thomas, MT Sullivan, C Avis, EM De Jong, W Hartford, DJ McCleese

The Diviner Lunar Radiometer Experiment on NASA's Lunar Reconnaissance Orbiter will be the first instrument to systematically map the global thermal state of the Moon and its diurnal and seasonal variability. Diviner will measure reflected solar and emitted infrared radiation in nine spectral channels with wavelengths ranging from 0.3 to 400 microns. The resulting measurements will enable characterization of the lunar thermal environment, mapping surface properties such as thermal inertia, rock abundance and silicate mineralogy, and determination of the locations and temperatures of volatile cold traps in the lunar polar regions. © The author(s) 2009.

An electric field sensor to measure charged dust on the Marco Polo asteroid sample return mission

International Astronautical Federation - 59th International Astronautical Congress 2008, IAC 2008 3 (2008) 1741-1748

KL Aplin, EC Sawyer, AJ Coates, DJ Parker, GH Jones, NE Bowles, MS Whalley

The Marco Polo mission has been selected by the European Space Agency (ESA) as a candidate for launch under the Cosmic Vision programme in -2017. The mission ultimately aims to understand the origins of the planets and even life itself, by returning a sample of material from a primitive asteroid, representative of the early Solar System. Particles on the surface of the asteroid are readily charged by photoelectric emission. Preliminary calculations suggest that photoelectric fields of tens of volts per metre are expected, and electrostatic transport, levitation, and even complete ejection from the asteroid's gravitational field seem likely for typical particles at the proposed candidate asteroids. The electrical and charged particle environment at the asteroid surface is therefore expected to be significant for sample selection and characterisation. The Asteroid Charge Experiment (ACE), comprising an electric field sensor to detect charged dust particles, and an electron spectrometer to measure both photoelectrons and electrons from the solar wind, is described here. ACE will also be able to determine the relative electrostatic potentials of the spacecraft and asteroid surface, which will quantify the electrical effects of the sampling process itself on the asteroid environment.

Band parameters for self-broadened ammonia gas in the range 0.74 to 5.24 μm to support measurements of the atmosphere of the planet Jupiter

Icarus 196 (2008) 612-624

N Bowles, S Calcutt, P Irwin, J Temple

We present new measurements and modelling of low-resolution transmission spectra of self-broadened ammonia gas, one of the most important absorbers found in the near-infrared spectrum of the planet Jupiter. These new spectral measurements were specifically designed to support measurements of Jupiter's atmosphere made by the Near-Infrared Mapping Spectrometer (NIMS) which was part of the Galileo mission that orbited Jupiter from 1995 to September 2003. To reach approximate jovian conditions in the lab, a new gas spectroscopy facility was developed and used to measure self-broadened ammonia spectra from 0.74 to 5.2 μm, virtually the complete range of the NIMS instrument, for the first time. Spectra were recorded at temperatures varying from 300 to 215 K, pressures from 1000 to 33 mb and using three different path lengths (10.164, 6.164 and 2.164 m). The spectra were then modelled using a series of increasingly complex physically based transmittance functions. © 2008 Elsevier Inc. All rights reserved.

Global and temporal variations in hydrocarbons and nitriles in Titan's stratosphere for northern winter observed by Cassini/CIRS

Icarus 193 (2008) 595-611

NA Teanby, PGJ Irwin, R de Kok, CA Nixon, A Coustenis, E Royer, SB Calcutt, NE Bowles, L Fletcher, C Howett, FW Taylor

Mid-infrared spectra measured by Cassini's Composite InfraRed Spectrometer (CIRS) between July 2004 and January 2007 (Ls = 293 ° - 328 °) have been used to determine stratospheric temperature and abundances of C2H2, C3H4, C4H2, HCN, and HC3N. Over 65,000 nadir spectra with spectral resolutions of 0.5 and 2.5 cm-1 were used to probe spatial and temporal composition variations in Titan's stratosphere. Cassini's 180° orbital transfer in mid-2006 allowed low emission angle observations of the north polar region for the first time in the mission and allowed us to probe the full latitude range. We present the first measurements of composition variations within the polar vortex, which display increasing abundances right up to 90° N. The lack of a homogeneous abundance-latitude variation within the vortex indicates limited horizontal mixing and suggests that subsidence is greatest at the vortex core. Contrary to numerical model predictions and tropospheric cloud observations, we do not see any evidence for a secondary circulation cell near the south pole, which suggests a single Hadley-type circulation in the stratosphere at this epoch. This difference can be reconciled if the secondary cell is restricted to altitudes below 100 km, where there is no sensitivity in our data. Temporal variations in composition were observed in the south, with volatile species becoming less abundant as the season progressed. The observed variations are compared to numerical model predictions and observations from Voyager. © 2007 Elsevier Inc. All rights reserved.

Temperature and composition of Saturn's polar hot spots and hexagon.

Science 319 (2008) 79-81

LN Fletcher, PGJ Irwin, GS Orton, NA Teanby, RK Achterberg, GL Bjoraker, PL Read, AA Simon-Miller, C Howett, R de Kok, N Bowles, SB Calcutt, B Hesman, FM Flasar

Saturn's poles exhibit an unexpected symmetry in hot, cyclonic polar vortices, despite huge seasonal differences in solar flux. The cores of both vortices are depleted in phosphine gas, probably resulting from subsidence of air into the troposphere. The warm cores are present throughout the upper troposphere and stratosphere at both poles. The thermal structure associated with the marked hexagonal polar jet at 77 degrees N has been observed for the first time. Both the warm cyclonic belt at 79 degrees N and the cold anticyclonic zone at 75 degrees N exhibit the hexagonal structure.

Characteristics of Titan's stratospheric aerosols and condensate clouds from Cassini CIRS far-infrared spectra

Icarus 191 (2007) 223-235

NE Bowles, N A Teanby, P G J Irwin, R de Kok

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.

Characterising Saturn's vertical temperature structure from Cassini/CIRS

Icarus 189 (2007) 457-478

NE Bowles, L N Fletcher, N A Teanby, P G J Irwin

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

Icarus 188 (2007) 72-88

NE Bowles, L N Fletcher, N A Teanby, P G J Irwin

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.

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

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