Publications by Neil Bowles

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.

Modelling of an asteroid photoelectron sheath and implications for a sample return mission


KL Aplin, AJ Macfaden, NE Bowles

On the potential of the EChO mission to characterize gas giant atmospheres

MNRAS 430 (2013) 1188-1207-1188-1207

JK Barstow, S Aigrain, PGJ Irwin, N Bowles, LN Fletcher, J-M Lee

Investigation of new band parameters with temperature dependence for self-broadened methane gas in the range 9000 to 14,000cm <sup>-1</sup> (0.71 to 1.1μm)

Journal of Quantitative Spectroscopy and Radiative Transfer 113 (2012) 763-782

N Bowles, R Passmore, K Smith, G Williams, S Calcutt, PGJ Irwin

This paper describes new measurements and modelling of the absorption of methane gas, one of the most important gases observed in the atmospheres of the outer planets and Titan, between 9000 and 14,000cm -1 (0.7 to 1.1μm) and compares them with current best available spectral models.A series of methane spectra were measured at the UK's Natural Environment Research Council (NERC) Molecular Spectroscopy Facility (based at the Rutherford Appleton Laboratory, Oxfordshire, UK) using a Brüker 125HR Fourier transform spectrometer. To approximate the conditions found in outer planet atmospheres, the spectra were measured over a wide range of pressures (5bar to 38mbar) and temperatures (290-100K) with path lengths of 19.3, 17.6, 16.0 and 14.4m. The spectra were recorded at a moderate resolution of 0.12cm -1 and then averaged to 10cm -1 resolution prior to fitting a series of increasingly complex band-models including temperature dependence. Using the most complex model, a Goody line distribution with a Voigt line shape and two lower energy state levels, the typical rms residual error in the fit is between 0.01 and 0.02 in the wings of the main absorption bands.The new spectral parameters were then compared with the measured spectra and spectra calculated using existing data and shown to be able to accurately reproduce the measured absorption. The improvement in the temperature dependence included in the model is demonstrated by comparison with existing cold methane spectral data for a typical Jovian path. © 2012 Elsevier Ltd.

Laboratory emissivity measurements of the plagioclase solid solution series under varying environmental conditions

Journal of Geophysical Research E: Planets 117 (2012)

KL Donaldson Hanna, IR Thomas, NE Bowles, BT Greenhagen, CM Pieters, JF Mustard, CRM Jackson, MB Wyatt

New laboratory thermal infrared emissivity measurements of the plagioclase solid solution series over the 1700∼400cm -1 (6-25m) spectral range are presented. Thermal infrared (TIR) spectral changes for fine-particulate samples (0-25m) are characterized for the first time under different laboratory environmental conditions: ambient (terrestrial-like), half-vacuum (Mars-like), vacuum, and vacuum with cooled chamber (lunar-like). Under all environmental conditions the Christiansen Feature (CF) is observed to vary in a systematic way with Na-rich end-member (albite) having a CF position at the highest wave number (shortest wavelength) and the Ca-rich end-member (anorthite) having a CF position with the lowest wave number (longest wavelength). As pressure decreases to < 10 -3 mbar four observations are made: (1) the CF position shifts to higher wave numbers, (2) the spectral contrast of the CF increases relative to the RB, (3) the spectral contrast of the RB in the ∼1200-900 spectral range decreases while the spectral contrast of the RB in the ∼800-400 spectral range either increases or remains the same and (4) the TF disappears. A relationship between the wavelength position of the CF measured under simulated lunar conditions and plagioclase composition (An#) is developed. Although its exact form may evolve with additional data, this linear relationship should be applied to current and future TIR data sets of the Moon. Our new spectral measurements demonstrate how sensitive thermal infrared emissivity spectra of plagioclase feldspars are to the environmental conditions under which they are measured and provide important constraints for interpreting current and future thermal infrared data sets. © 2012 American Geophysical Union. All Rights Reserved.

Thermal infrared emissivity measurements under a simulated lunar environment: Application to the Diviner Lunar Radiometer Experiment

Journal of Geophysical Research E: Planets 117 (2012)

KL Donaldson Hanna, MB Wyatt, IR Thomas, NE Bowles, BT Greenhagen, A Maturilli, J Helbert, DA Paige

We present new laboratory thermal infrared emissivity spectra of the major silicate minerals identified on the Moon measured under lunar environmental conditions and evaluate their application to lunar remote sensing data sets. Thermal infrared spectral changes between ambient and lunar environmental conditions are characterized for the first time over the 400∼1700 cm -1 (6-25 m) spectral range for a fine-particulate mineral suite including plagioclase (albite and anorthite), pyroxene (enstatite and augite), and olivine (forsterite). The lunar environment introduces observable effects in thermal infrared emissivity spectra of fine particulate minerals, which include: (1) a shift in the Christiansen feature (CF) position to higher wave numbers (shorter wavelengths), (2) an increase in the overall spectral contrast, and (3) decreases in the spectral contrast of the reststrahlen bands and transparency features. Our new measurements demonstrate the high sensitivity of thermal infrared emissivity spectra to environmental conditions under which they are measured and provide important constraints for interpreting new thermal infrared data sets of the Moon, including the Diviner Lunar Radiometer Experiment onboard NASA's Lunar Reconnaissance Orbiter. Full resolution laboratory mineral spectra convolved to Diviner's three spectral channels show that spectral shape, CF position and band ratios can be used to distinguish between individual mineral groups and lunar lithologies. The integration of the thermal infrared CF position with near infrared spectral parameters allows for robust mineralogical identifications and provides a framework for future integrations of data sets across two different wavelength regimes. Copyright 2012 by the American Geophysical Union.

A new experimental setup for making thermal emission measurements in a simulated lunar environment.

Rev Sci Instrum 83 (2012) 124502-

IR Thomas, BT Greenhagen, NE Bowles, KL Donaldson Hanna, J Temple, SB Calcutt

One of the key problems in determining lunar surface composition for thermal-infrared measurements is the lack of comparable laboratory-measured spectra. As the surface is typically composed of fine-grained particulates, the lunar environment induces a thermal gradient within the near sub-surface, altering the emission spectra: this environment must therefore be simulated in the laboratory, considerably increasing the complexity of the measurement. Previous measurements have created this thermal gradient by either heating the cup in which the sample sits or by illuminating the sample using a solar-like source. This is the first setup able to measure in both configurations, allowing direct comparisons to be made between the two. Also, measurements across a wider spectral range and at a much higher spectral resolution can be acquired using this new setup. These are required to support new measurements made by the Diviner Lunar Radiometer, the first multi-spectral thermal-infrared instrument to orbit the Moon. Results from the two different heating methods are presented, with measurements of a fine-grained quartz sample compared to previous similar measurements, plus measurements of a common lunar highland material, anorthite. The results show that quartz gives the same results for both methods of heating, as predicted by previous studies, though the anorthite spectra are different. The new calibration pipeline required to convert the raw data into emissivity spectra is described also.

Investigation of new band parameters with temperature dependence for self-broadened methane gas in the range 9000 to 14,000 cm -1 (0.71 to 1.1 μm)

Journal of Quantitative Spectroscopy and Radiative Transfer (2012)

N Bowles, R Passmore, K Smith, G Williams, S Calcutt, PGJ Irwin

Lunar regolith thermal gradients and emission spectra: Modeling and validation

Journal of Geophysical Research E: Planets 116 (2011)

L Millán, I Thomas, N Bowles

The retrieval of surface composition from IR measurements of airless bodies requires a model capable of computing the significant thermal gradients present in the top few hundred microns of the regolith. In this study we introduce a model which reproduces most of the features found in controlled experiments made in the simulated lunar environment emission chamber (SLEEC). Although the model presented here is forced by a lower boundary held at a fixed temperature, we conclude that a similar algorithm driven by solar illumination may be used as a forward model to retrieve composition, particle size and effective thermal conductivity from IR measurements of airless bodies. Copyright 2011 by the American Geophysical Union.

Asteroid electrostatic instrumentation and modelling

Journal of Physics: Conference Series 301 (2011)

KL Aplin, NE Bowles, E Urbak, D Keane, EC Sawyer

Asteroid surface material is expected to become photoelectrically charged, and is likely to be transported through electrostatic levitation. Understanding any movement of the surface material is relevant to proposed space missions to return samples to Earth for detailed isotopic analysis. Motivated by preparations for the Marco Polo sample return mission, we present electrostatic modelling for a real asteroid, Itokawa, for which detailed shape information is available, and verify that charging effects are likely to be significant at the terminator and at the edges of shadow regions for the Marco Polo baseline asteroid, 1999JU3. We also describe the Asteroid Charge Experiment electric field instrumentation intended for Marco Polo. Finally, we find that the differing asteroid and spacecraft potentials on landing could perturb sample collection for the short landing time of 20min that is currently planned.

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.

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.

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

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 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 (L s = 293 ° - 328 °) have been used to determine stratospheric temperature and abundances of C 2 H 2 , C 3 H 4 , C 4 H 2 , HCN, and HC 3 N. 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 b elow 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.

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