Publications by Neil Bowles

Comparing thermal infrared spectral unmixing algorithms: applications to Bennu and other airless bodies

Meteoritics and Planetary Science Wiley 54 (2019)

EC Brown, KLD Hanna, N Bowles, VE Hamilton, BE Clark, AD Rogers, DS Lauretta

Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Nature Astronomy Springer Nature 3 (2019) 332-340

VE Hamilton, PR Christensen, MA Barucci, DC Reuter, AA Simon, BE Clark, N Bowles, WV Boynton, EA Cloutis, KLD Hannah, JP Emery, HL Enos, CHC Jr, S Fornasier, CW Haberle, ES Howell, HH Kaplan, RD Hanna, LP Keller, C Lantz, TJ McCoy, LF Lim, J-Y Li, MC Nolan

Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth.

Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis

Nature Astronomy Springer Nature 3 (2019) 341-351

DN Dellagiustina, MA Barucci, EB Bierhaus, RP Binzel, N Bowles, WF Bottke, H Campins, BC Clark, BE Clark, CHC Jr, J De Leon, JDP Deshapriya, M Delbo', CM Elder, CW Hergenrother, S Fornasier, P Michel, M Pajola, Y Fernandez, W Chang, A Cheuvront, D Trang, S Tachibana, H Yurimoto

Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA’s Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu’s surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu’s moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu’s surface particles span from the disruption of the asteroid’s parent body (boulders) to recent in situ production (micrometre-scale particles).

Small bodies science with the Twinkle space telescope


B Edwards, S Lindsay, G Savini, G Tinetti, C Arena, N Bowles, M Tessenyi

Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface

Nature Geoscience Springer Nature 12 (2019) 242-246

S Clemett, K Thomas-Keprta, S Van Wal, M Yoshikawa, J Bellerose, S Bhaskaran, C Boyles, CM Elder, D Farnocchia, A Harbison, A Knight, B Kennedy, N Martinez-Vlasoff, N Mastrodemos, T McElrath, W Owen, R Park, L Swanson, B Rush, Y Takahashi, K Yetter, D Velez, C Thayer, C Adam

Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennu’s expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennu’s time in the main asteroid belt.

Evidence for ultra-cold traps and surface water ice in the lunar south polar crater Amundsen

Icarus Elsevier 332 (2019) 1-13

E Sefton-Nash, J-P Williams, BT Greenhagen, TJ Warren, K-M Aye, JL Bandfield, F Leader, MA Siegler, PO Hayne, N Bowles, DA Paige

The northern floor and wall of Amundsen crater, near the lunar south pole, is a permanently shaded region (PSR). Previous study of this area using data from the Lunar Orbiter Laser Altimeter (LOLA), Diviner and LAMP instruments aboard Lunar Reconnaissance Orbiter (LRO) shows a spatial correlation between brighter 1064 nm albedo, annual maximum surface temperatures low enough to enable persistence of surface water ice (<110 K), and anomalous ultraviolet radiation. We present results using data from Diviner that quantify the differential emissivities observed in the far-IR (near the Planck peak for PSR-relevant temperatures) between the PSR and a nearby non-PSR target in Amundsen Crater. We find features in far-IR emissivity (50–400 μm) could be attributed to either, or a combination, of two effects (i) differential regolith emissive behavior between permanently-shadowed temperature regimes and those of normally illuminated polar terrain, perhaps related to presence of water frost (as indicated in other studies), or (ii) high degrees of anisothermality within observation fields of view caused by doubly-shaded areas within the PSR target that are colder than observed brightness temperatures. The implications in both cases are compelling: The far-IR emissivity curve of lunar cold traps may provide a metric for the abundance of “micro” cold traps that are ultra-cool, i.e. shadowed also from secondary and higher order radiation (absorption and re-radiation or scattering by surrounding terrain), or for emissive properties consistent with the presence of surface water ice.

Linking mineralogy and spectroscopy of highly aqueously altered CM and CI carbonaceous chondrites in preparation for primitive asteroid sample return

Meteoritics and Planetary Science Wiley (2019)

H Bates, AJ King, KL Donaldson Hanna, NE Bowles, SS Russell

The operational environment and rotational acceleration of asteroid (101955) Bennu from OSIRIS-REx observations

Nature Communications Springer Nature 10 (2019) 1291

CK Maleszewski, MC Nolan, J-Y Li, CY Drouet D'Aubigny, FC Shelly, CM Hartzell, B Rizk, DJ Scheeres, PH Smith, DS Lauretta, X-D Zou, ES Howell, TR Kareta, MRM Izawa, MA Barucci, EB Bierhaus, BE Clark, EJ Christensen, DN Dellagiustina, S Fornasier, CW Hergenrother, H Campins

During its approach to asteroid (101955) Bennu, NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed Bennu's immediate environment, photometric properties, and rotation state. Discovery of a dusty environment, a natural satellite, or unexpected asteroid characteristics would have had consequences for the mission's safety and observation strategy. Here we show that spacecraft observations during this period were highly sensitive to satellites (sub-meter scale) but reveal none, although later navigational images indicate that further investigation is needed. We constrain average dust production in September 2018 from Bennu's surface to an upper limit of 150 g s-1 averaged over 34 min. Bennu's disk-integrated photometric phase function validates measurements from the pre-encounter astronomical campaign. We demonstrate that Bennu's rotation rate is accelerating continuously at 3.63 ± 0.52 × 10-6 degrees day-2, likely due to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, with evolutionary implications.

Modeling the angular dependence of emissivity of randomly rough surfaces

Journal of Geophysical Research American Geophysical Union 124 (2019) 585-601

T Warren, N Bowles, K Donaldson Hanna, J Bandfield

Directional emissivity (DE) describes how the emissivity of an isothermal surface changes with viewing angle across thermal infrared wavelengths. The Oxford Space Environment Goniometer (OSEG) is a novel instrument that has been specifically designed to measure the DE of regolith materials derived from planetary surfaces. The DE of Nextel high emissivity black paint was previously measured by the OSEG and showed that the measured emissivity decreases with increasing emission angle, from an emissivity of 0.97 ± 0.01 at 0° emission angle to an emissivity of 0.89± 0.01 at 71° emission angle. The Nextel target measured was isothermal (<0.1 K surface temperature variation) and the observed change in emissivity was due to Fresnel related effects and was not due to non-isothermal effects. Here we apply several increasingly complex modelling techniques to model the measured DE of Nextel black paint. The modelling techniques used here include the Hapke DE model, the Fresnel equations, a multiple slope Fresnel model and a Monte Carlo ray-tracing model. It was found that only the Monte Carlo raytracing model could accurately fit the OSEG measured Nextel data. We show that this is because the Monte Carlo ray-tracing model is the only model that fully accounts for the surface roughness of the Nextel surface by including multiple scattering effects.

SEIS: Insight's Seismic Experiment for Internal Structure of Mars


P Lognonne, WB Banerdt, D Giardini, WT Pike, U Christensen, P Laudet, S de Raucourt, P Zweifel, S Calcutt, M Bierwirth, KJ Hurst, F Ijpelaan, JW Umland, R Llorca-Cejudo, SA Larson, RF Garcia, S Kedar, B Knapmeyer-Endrun, D Mimoun, A Mocquet, MP Panning, RC Weber, A Sylvestre-Baron, G Pont, N Verdier, L Kerjean, LJ Facto, V Gharakanian, JE Feldman, TL Hoffman, DB Klein, K Klein, NP Onufer, J Paredes-Garcia, MP Petkov, JR Willis, SE Smrekar, M Drilleau, T Gabsi, T Nebut, O Robert, S Tillier, C Moreau, M Parise, G Aveni, S Ben Charef, Y Bennour, T Camus, PA Dandonneau, C Desfoux, B Lecomte, O Pot, P Revuz, D Mance, J tenPierick, NE Bowles, C Charalambous, AK Delahunty, J Hurley, R Irshad, H Liu, AG Mukherjee, IM Standley, AE Stott, J Temple, T Warren, M Eberhardt, A Kramer, W Kuehne, E-P Miettinen, M Monecke, C Aicardi, M Andre, J Baroukh, A Borrien, A Bouisset, P Boutte, K Brethome, C Brysbaert, T Carlier, M Deleuze, JM Desmarres, D Dilhan, C Doucet, D Faye, N Faye-Refalo, R Gonzalez, C Imbert, C Larigauderie, E Locatelli, L Luno, J-R Meyer, F Mialhe, JM Mouret, M Nonon, Y Pahn, A Paillet, P Pasquier, G Perez, R Perez, L Perrin, B Pouilloux, A Rosak, IS de Larclause, J Sicre, M Sodki, N Toulemont, B Vella, C Yana, F Alibay, OM Avalos, MA Balzer, P Bhandari, E Blanco, BD Bone, JC Bousman, P Bruneau, FJ Calef, RJ Calvet, SA D'Agostino, G de los Santos, RG Deen, RW Denise, J Ervin, NW Ferraro, HE Gengl, F Grinblat, D Hernandez, M Hetzel, ME Johnson, L Khachikyan, JY Lin, SM Madzunkov, SL Marshall, IG Mikellides, EA Miller, W Raff, JE Singer, CM Sunday, JF Villalvazo, MC Wallace, D Banfield, JA Rodriguez-Manfredi, CT Russell, A Trebi-Ollennu, JN Maki, E Beucler, M Bose, C Bonjour, JL Berenguer, S Ceylan, J Clinton, V Conejero, I Daubar, V Dehant, P Delage, F Euchner, I Esteve, L Fayon, L Ferraioli, CL Johnson, J Gagnepain-Beyneix, M Golombek, A Khan, T Kawamura, B Kenda, P Labrot, N Murdoch, C Pardo, C Perrin, L Pou, A Sauron, D Savoie, S Stahler, E Stutzmann, NA Teanby, J Tromp, M van Driel, M Wieczorek, R Widmer-Schnidrig, J Wookey

Spectral characterization of analog samples in anticipation of OSIRIS-REx's arrival at Bennu: A blind test study

Icarus Elsevier 319 (2018) 701-723

KL Donaldson Hanna, DL Schrader, EA Cloutis, DM Applin, JP Mann, NE Bowles, LP Keller, LF Lim, BE Clark, VE Hamilton, C Lantz, SS Russell, PF Schofield, GD Cody, AJ King, TJ McCoy, HC Connolly, E Dotto, DS Lauretta

We present spectral measurements of a suite of mineral mixtures and meteorites that are possible analogs for asteroid (101955) Bennu, the target asteroid for NASA's Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) mission. The sample suite, which includes anhydrous and hydrated mineral mixtures and a suite of chondritic meteorites (CM, CI, CV, CR, and L5), was chosen to characterize the spectral effects due to varying amounts of aqueous alteration and minor amounts of organic material. Our results demonstrate the utility of mineral mixtures for understanding the mixing behavior of meteoritic materials and identifying spectrally dominant species across the visible to near-infrared (VNIR) and thermal infrared (TIR) spectral ranges. Our measurements demonstrate that, even with subtle signatures in the spectra of chondritic meteorites, we can identify diagnostic features related to the minerals comprising each of the samples. Also, the complementary nature of the two spectral ranges regarding their ability to detect different mixture and meteorite components can be used to characterize analog sample compositions better. However, we observe differences in the VNIR and TIR spectra between the mineral mixtures and the meteorites. These differences likely result from (1) differences in the types and physical disposition of constituents in the mixtures versus in meteorites, (2) missing phases observed in meteorites that we did not add to the mixtures, and (3) albedo differences among the samples. In addition to the initial characterization of the analog samples, we will use these spectral measurements to test phase detection and abundance determination algorithms in anticipation of mapping Bennu's surface properties and selecting a sampling site.

The unexpected surface of asteroid (101955) Bennu

Nature Springer Nature 568 (2019) 55-60

DS Lauretta, CA Bennett, SS Balram-Knutson, TL Becker, WF Bottke, H Campins, BE Clark, HC Connolly, CY Drouet D'Aubigny, JP Dworkin, JP Emery, HL Enos, MRM Izawa, HH Kaplan, CWV Wolner, N Bowles, DJ Scheeres, PH Smith, MC Nolan, B Rizk, HL Roper, KJ Walsh, DN Dellagiustina

NASA'S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth1. Bennu is a low-albedo B-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine-that is, not affected by these processes4. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu's global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5-11. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid's properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu's thermal inertia12 and radar polarization ratios13-which indicated a generally smooth surface covered by centimetre-scale particles-resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.

The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements

Nature Astronomy Springer Nature 3 (2019) 352-361

J Joseph, S Squyres, D Richardson, JP Emery, L McGraw, R Ghent, RP Binzel, L Philpott, EA Cloutis, RD Hanna, CHC Jr, F Ciceri, E-M Ibrahim, D Velez, C Bryan, D Wibben, D Ellis, P Falkenstern, A Fisher, ME Fisher, C Parish, M Ryle, M Schmitzer, P Sherman, M Skeen

The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to the formation of binary asteroids.

Remote-sensing characterization of major Solar System bodies with the Twinkle space telescope

Journal of Astronomical Telescopes Instruments and Systems SPIE 5 (2019) 014006

B Edwards, S Lindsay, G Savini, G Tinetti, C Arena, N Bowles, M Tessenyi

Remote-sensing observations of Solar System objects with a space telescope offer a key method of understanding celestial bodies and contributing to planetary formation and evolution theories. The capabilities of Twinkle, a space telescope in a low Earth orbit with a 0.45-m mirror, to acquire spectroscopic data of Solar System targets in the visible and infrared are assessed. Twinkle is a general observatory that provides on-demand observations of a wide variety of targets within wavelength ranges that are currently not accessible using other space telescopes or that are accessible only to oversubscribed observatories in the short-term future. We determine the periods for which numerous Solar System objects could be observed and find that Solar System objects are regularly observable. The photon flux of major bodies is determined for comparison to the sensitivity and saturation limits of Twinkle's instrumentation and we find that the satellite's capability varies across the three spectral bands (0.4 to 1, 1.3 to 2.42, and 2.42 to 4.5 μm). We find that for a number of targets, including the outer planets, their large moons, and bright asteroids, the model created predicts that with short exposure times, high-resolution spectra (R ~ 250, λ < 2.42 μm; R ~ 60, λ > 2.42 μm) could be obtained with signal-to-noise ratio (SNR) of > 100 with exposure times of <300 s. For other targets (e.g., Phobos), an SNR > 10 would be achievable in 300 s (or less) for spectra at Twinkle's native resolution. Fainter or smaller targets (e.g., Pluto) may require multiple observations if resolution or data quality cannot be sacrificed. Objects such as the outer dwarf planet Eris are deemed too small, faint or distant for Twinkle to obtain photometric or spectroscopic data of reasonable quality (SNR > 10) without requiring large amounts of observation time. Despite this, the Solar System is found to be permeated with targets that could be readily observed by Twinkle.

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

Icarus Elsevier 321 (2018) 572-582

P Irwin, N Bowles, A Braude, S Calcutt, R Garland, PA Coles, J Tennyson

An analysis of currently available ammonia (NH3) visible-to-near-infrared gas absorption data was recently undertaken by Irwin et al. (2018) to help interpret Very Large Telescope (VLT) MUSE observations of Jupiter from 0.48–0.93 µm, made in support of the NASA/Juno mission. Since this analysis a newly revised set of ammonia line data, covering the previously poorly constrained range 0.5–0.833 µm, has been released by the ExoMol project, “C2018” (Coles et al., 2018), which demonstrates significant advantages over previously available data sets, and provides for the first time complete line data for the previously poorly constrained 5520- and 6475-Å bands of NH3. In this paper we compare spectra calculated using the ExoMol–C2018 data set (Coles et al., 2018) with spectra calculated from previous sources to demonstrate its advantages. We conclude that at the present time the ExoMol–C2018 dataset provides the most reliable ammonia absorption source for analysing low- to medium-resolution spectra of Jupiter in the visible/near-IR spectral range, but note that the data are less able to model high-resolution spectra owing to small, but significant inaccuracies in the line wavenumber estimates. This work is of significance not only for solar system planetary physics, but for future proposed observations of Jupiter-like planets orbiting other stars, such as with NASA’s planned Wide-Field Infrared Survey Telescope (WFIRST).

The ARIEL space mission

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 10698 (2018)
Part of a series from Proceedings of SPIE

N Bezawada, E Pascale, J-P Beaulieu, J Barstow, N Bowles, V Coudé Du Foresto, A Coustenis, L Decin, P Drossart, P Eccleston, T Encrenaz, F Forget, M Griffin, M Güdel, P Hartogh, P-O Lagage, A Heske, J Leconte, P Malaguti, G Micela, K Middleton, M Min, A Moneti, JC Morales, M Ollivier

The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey, ARIEL, has been selected to be the next M4 space mission in the ESA Cosmic Vision programme. From launch in 2028, and during the following 4 years of operation, ARIEL will perform precise spectroscopy of the atmospheres of about 1000 known transiting exoplanets using its metre-class telescope, a three-band photometer and three spectrometers that will cover the 0.5 μm to 7.8 μm region of the electromagnetic spectrum. The payload is designed to perform primary and secondary transit spectroscopy, and to measure spectrally resolved phase curves with a stability of < 100 ppm (goal 10 ppm). Observing from an L2 orbit, ARIEL will provide the first statistically significant spectroscopic survey of hot and warm planets. These are an ideal laboratory in which to study the chemistry, the formation and the evolution processes of exoplanets, to constrain the thermodynamics, composition and structure of their atmospheres, and to investigate the properties of the clouds.

Isolation of seismic signal from InSight/SEIS-SP microseismometer measurements

Space Science Reviews Springer 214 (2018) 95-

D Mimoun, WT Pike, N Murdoch, NA Teanby, N Bowles, TJ Warren, SB Calcutt, J Hurley

The InSight mission is due to launch in May 2018, carrying a payload of novel instruments designed and tested to probe the interior of Mars whilst deployed directly on the Martian regolith and partially isolated from the Martian environment by the Wind and Thermal Shield. Central to this payload is the seismometry package SEIS consisting of two seismometers, which is supported by a suite of environmental/meteorological sensors (Temperature and Wind Sensor for InSight TWINS; and Auxiliary Payload Sensor Suite APSS). In this work, an optimal estimations inversion scheme which aims to decorrelate the short-period seismometer (SEIS-SP) signal due to seismic activity alone from the environmental signal and random noise is detailed, and tested on both simulated and Viking data. This scheme also applies a module to identify measurements contaminated by Single Event Phenomena (SEP). This scheme will be deployed as the pre-processing pipeline for all SEIS-SP data prior to release to the scientific community for analysis.

The proposed Caroline ESA M3 mission to a Main Belt Comet

Advances in Space Research Elsevier 62 (2018) 1921-1946

GH Jones, J Agarwal, N Bowles, M Burchell, AJ Coates, A Fitzsimmons, A Graps, HH Hsieh, CM Lisse, SC Lowry, A Masters, C Snodgrass, C Tubiana

We describe Caroline, a mission proposal submitted to the European Space Agency in 2010 in response to the Cosmic Visions M3 call for medium-sized missions. Caroline would have travelled to a Main Belt Comet (MBC), characterizing the object during a flyby, and capturing dust from its tenuous coma for return to Earth. MBCs are suspected to be transition objects straddling the traditional boundary between volatile–poor rocky asteroids and volatile–rich comets. The weak cometary activity exhibited by these objects indicates the presence of water ice, and may represent the primary type of object that delivered water to the early Earth. The Caroline mission would have employed aerogel as a medium for the capture of dust grains, as successfully used by the NASA Stardust mission to Comet 81P/Wild 2. We describe the proposed mission design, primary elements of the spacecraft, and provide an overview of the science instruments and their measurement goals. Caroline was ultimately not selected by the European Space Agency during the M3 call; we briefly reflect on the pros and cons of the mission as proposed, and how current and future mission MBC mission proposals such as Castalia could best be approached.

A chemical survey of exoplanets with ARIEL

Experimental Astronomy Springer 46 (2018) 135–209-

G Tinetti, P Drossart, P Eccleston, P Hartogh, A Heske, J Leconte, G Micela, M Ollivier, P Eccleston, G Pilbratt, L Puig, D Turrini, N Bowles

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. The Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) has been selected by the European Space Agency as the next mediumclass science mission, M4, to address these scientific questions. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25-7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10-100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.

The Oxford space environment goniometer: A new experimental setup for making directional emissivity measurements under a simulated space environment

Review of Scientific Instruments American Institute of Physics 88 (2017) 124502-

TJ Warren, NE Bowles, K Donaldson Hanna, IR Thomas

Measurements of the light scattering behaviour of the regoliths of airless bodies via remote sensing techniques in the Solar System, across wavelengths from the visible to the far infrared, are essential in understanding their surface properties. A key parameter is knowledge of the angular behaviour of scattered light, usually represented mathematically by a phase function. The phase function is believed to be dependent on many factors including the following: surface composition, surface roughness across all length scales, and the wavelength of radiation. Although there have been many phase function measurements of regolith analog materials across visible wavelengths, there have been no equivalent measurements made in the thermal infrared (TIR). This may have been due to a lack of TIR instruments as part of planetary remote sensing payloads. However, since the launch of Diviner to the Moon in 2009, OSIRIS-Rex to the asteroid Bennu in 2016, and the planned launch of BepiColombo to Mercury in 2018, there is now a large quantity of TIR remote sensing data that need to be interpreted. It is therefore important to extend laboratory phase function measurements to the TIR. This paper describes the design, build, calibration, and initial measurements from a new laboratory instrument that is able to make phase function measurements of analog planetary regoliths across wavelengths from the visible to the TIR.