Publications by Neil Bowles


Studying the Composition and Mineralogy of the Hermean Surface with the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) for the BepiColombo Mission: An Update

Space Science Reviews 216 (2020)

H Hiesinger, J Helbert, G Alemanno, KE Bauch, M D’Amore, A Maturilli, A Morlok, MP Reitze, C Stangarone, AN Stojic, I Varatharajan, I Weber, G Arnold, M Banaszkiewicz, K Bauch, J Benkhoff, A Bischoff, M Blecka, N Bowles, S Calcutt, L Colangeli, S Erard, S Fonti, BT Greenhagen, O Groussain, J Helbert, H Hiesinger, H Hirsch, J Jahn, R Killen, J Knollenberg, E Kührt, E Lorenz, I Mann, U Mall, A Maturilli, A Morlok, L Moroz, G Peter, M Rataj, M Robinson, W Skrbek, T Spohn, A Sprague, D Stöffler, A Stojic, F Taylor, I Varatharajan, H Venus, J Warrell, I Walter, I Weber, A Witzke, C Wöhler

© 2020, The Author(s). Launched onboard the BepiColombo Mercury Planetary Orbiter (MPO) in October 2018, the Mercury Radiometer and Thermal Infrared Spectrometer (MERTIS) is on its way to planet Mercury. MERTIS consists of a push-broom IR-spectrometer (TIS) and a radiometer (TIR), which operate in the wavelength regions of 7-14 μm and 7-40 μm, respectively. This wavelength region is characterized by several diagnostic spectral signatures: the Christiansen feature (CF), Reststrahlen bands (RB), and the Transparency feature (TF), which will allow us to identify and map rock-forming silicates, sulfides as well as other minerals. Thus, the instrument is particularly well-suited to study the mineralogy and composition of the hermean surface at a spatial resolution of about 500 m globally and better than 500 m for approximately 5-10% of the surface. The instrument is fully functional onboard the BepiColombo spacecraft and exceeds all requirements (e.g., mass, power, performance). To prepare for the science phase at Mercury, the team developed an innovative operations plan to maximize the scientific output while at the same time saving spacecraft resources (e.g., data downlink). The upcoming fly-bys will be excellent opportunities to further test and adapt our software and operational procedures. In summary, the team is undertaking action at multiple levels, including performing a comprehensive suite of spectroscopic measurements in our laboratories on relevant analog materials, performing extensive spectral modeling, examining space weathering effects, and modeling the thermal behavior of the hermean surface.


The Oxford 3D thermophysical model with application to PROSPECT/Luna 27 study landing sites

Planetary and Space Science Elsevier 182 (2019) 104790

O King, T Warren, N Bowles, E Sefton-Nash, R Fisackerly, R Trautner

A 3D thermal model that includes a discrete subsurface exponential density profile, surface shadowing and scattering effects has been developed to simulate surface and subsurface temperatures across the Moon. Comparisons of the modelled surface temperatures with the Lunar Reconnaissance Orbiter’s Diviner Lunar Radiometer Experiment (“Diviner”) measured temperatures show significant improvements in model accuracy from the inclusion of shadowing and scattering effects, with model errors reduced from ~10 K to ~2 K for mid-latitude craters. The 3D thermal model is used to investigate ice stability at potential landing sites near the lunar south pole, studied for Roscosmos’ ‘Luna Resource’ (Luna 27) lander mission on which the ESA PROSPECT payload is planned to fly. Water ice is assumed to be stable for long periods of time (>1 Gyr) if temperatures remain below 112 K over diurnal and seasonal cycles. Simulations suggest ice can be stable at the surface in regions near to potential landing sites in permanently shaded regions and can be stable below the surface in partly shaded regions such as pole-facing slopes. The simulated minimum constant subsurface temperature (where the seasonal temperature cycle is attenuated) typically occurs at a depth of ~50 cm and therefore the minimum depth where ice can be stable is A 3D thermal model that includes a discrete subsurface exponential density profile, surface shadowing and scattering effects has been developed to simulate surface and subsurface temperatures across the Moon. Comparisons of the modelled surface temperatures with the Lunar Reconnaissance Orbiter’s Diviner Lunar Radiometer Experiment (“Diviner”) measured temperatures show significant improvements in model accuracy from the inclusion of shadowing and scattering effects, with model errors reduced from ~10 K to ~2 K for mid-latitude craters. The 3D thermal model is used to investigate ice stability at potential landing sites near the lunar south pole, studied for Roscosmos’ ‘Luna Resource’ (Luna 27) lander mission on which the ESA PROSPECT payload is planned to fly. Water ice is assumed to be stable for long periods of time (>1 Gyr) if temperatures remain below 112 K over diurnal and seasonal cycles. Simulations suggest ice can be stable at the surface in regions near to potential landing sites in permanently shaded regions and can be stable below the surface in partly shaded regions such as pole-facing slopes. The simulated minimum constant subsurface temperature (where the seasonal temperature cycle is attenuated) typically occurs at a depth of ~50 cm and therefore the minimum depth where ice can be stable is 0<z<50cm.


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


Author Correction: Shape of (101955) Bennu indicative of a rubble pile with internal stiffness (Nature Geoscience, (2019), 12, 4, (247-252), 10.1038/s41561-019-0330-x)

Nature Geoscience (2020)

OS Barnouin, MG Daly, EE Palmer, RW Gaskell, JR Weirich, CL Johnson, MM Al Asad, JH Roberts, ME Perry, HCM Susorney, RT Daly, EB Bierhaus, JA Seabrook, RC Espiritu, AH Nair, L Nguyen, GA Neumann, CM Ernst, WV Boynton, MC Nolan, CD Adam, MC Moreau, B Rizk, CY Drouet D’Aubigny, ER Jawin, KJ Walsh, P Michel, SR Schwartz, RL Ballouz, EM Mazarico, DJ Scheeres, JW McMahon, WF Bottke, S Sugita, N Hirata, N Hirata, SI Watanabe, KN Burke, DN DellaGiustina, CA Bennett, DS Lauretta, DE Highsmith, J Small, D Vokrouhlický, NE Bowles, E Brown, KL Donaldson Hanna, T Warren, C Brunet, RA Chicoine, S Desjardins, D Gaudreau, T Haltigin, S Millington-Veloza, A Rubi, J Aponte, N Gorius, A Lunsford, B Allen, J Grindlay, D Guevel, D Hoak, J Hong, DL Schrader, J Bayron, O Golubov, P Sánchez, J Stromberg, M Hirabayashi, CM Hartzell, S Oliver, M Rascon, A Harch, J Joseph, S Squyres, D Richardson, JP Emery, L McGraw, R Ghent, RP Binzel, MMA Asad, CL Johnson, L Philpott, EA Cloutis, RD Hanna, HC Connolly, F Ciceri, AR Hildebrand, EM Ibrahim, L Breitenfeld, T Glotch, AD Rogers, BE Clark, S Ferrone, CA Thomas, H Campins, Y Fernandez, W Chang, A Cheuvront

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. In the version of this Article originally published, in Table 1, there was an error in the ‘Period (equatorial J2000)’ parameter value. The value ‘4.276057’ should have been ‘4.296057’. Also, in the third paragraph of the main text, in the fifth sentence, the value ‘4.276057’ should have been ‘4.296059’. These have now been corrected in all versions of the Article. *A list of participants and their affiliations appears in the online version of the paper.


Initial results from the InSight mission on Mars

Nature Geoscience Springer Nature 13 (2020) 183-189

D Banfield, GS Collins, I Daubar, J Grygorczuk, S King, M Lemmon, JN Maki, SM McLennan, C Michaut, A Mittelholz, A Mocquet, P Morgan, NT Mueller, N Murdoch, F Nimmo, WT Pike, A-C Plesa, S Rodriguez, JA Rodriguez-Manfredi, N Schmerr, N Teanby, J Tromp, M van Driel, N Warner, M Wieczorek

NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indicate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander.


Publisher Correction: Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface (Nature Geoscience, (2019), 10.1038/s41561-019-0326-6)

Nature Geoscience 12 (2019) 399-

KJ Walsh, ER Jawin, RL Ballouz, OS Barnouin, EB Bierhaus, HC Connolly, JL Molaro, TJ McCoy, M Delbo’, CM Hartzell, M Pajola, SR Schwartz, D Trang, E Asphaug, KJ Becker, CB Beddingfield, CA Bennett, WF Bottke, KN Burke, BC Clark, MG Daly, DN DellaGiustina, JP Dworkin, CM Elder, DR Golish, AR Hildebrand, R Malhotra, J Marshall, P Michel, MC Nolan, ME Perry, B Rizk, A Ryan, SA Sandford, DJ Scheeres, HCM Susorney, F Thuillet, DS Lauretta, DE Highsmith, J Small, D Vokrouhlický, NE Bowles, E Brown, KLD Hanna, T Warren, C Brunet, RA Chicoine, S Desjardins, D Gaudreau, T Haltigin, S Millington-Veloza, A Rubi, J Aponte, N Gorius, A Lunsford, B Allen, J Grindlay, D Guevel, D Hoak, J Hong, DL Schrader, J Bayron, O Golubov, P Sánchez, J Stromberg, M Hirabayashi, S Oliver, M Rascon, A Harch, J Joseph, S Squyres, D Richardson, JP Emery, L McGraw, R Ghent, RP Binzel, MMA Asad, CL Johnson, L Philpott, EA Cloutis, RD Hanna, F Ciceri, EM Ibrahim, L Breitenfeld, T Glotch, AD Rogers, BE Clark, S Ferrone, CA Thomas, H Campins, Y Fernandez, W Chang, A Cheuvront, S Tachibana, H Yurimoto, JR Brucato, G Poggiali, E Dotto, EM Epifani, MK Crombie

© 2019, Springer Nature Limited. In the version of this Article originally published, in the sentence “There are three identified boulders with long axes exceeding 40 m and more than 200 boulders larger than 10 m2”, the term “10 m2” should have been “10 m (ref.2)”. This has now been corrected.


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

Meteoritics and Planetary Science Wiley 54 (2019)

EC Brown, K Donaldson Hanna, NE Bowles, VE Hamilton, BE Clark, AD Rogers, DS Lauretta, OSIRIS-REx Team


Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Nature Astronomy Springer Nature 3 (2019) 332-340

PR Christensen, DC Reuter, BE Clark, MA Barucci, CHC Jr, KLD Hannah, JP Emery, HL Enos, S Fornasier, Sandford, DL Schrader, X-D Zou, DS Lauretta, N Gorius, A Lunsford, D Hoak, J Hong, J Bayron, J Stromberg, M Hirabayashi, CM Hartzell, AR Hildebrand, J Nelson, R Pennington, G Libourel

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

X-D Zou, DS Lauretta, E Brown, KLD Hanna, T Warren, J Bellerose, D Farnocchia, A Harbison, B Kennedy, T McElrath, W Owen, B Rush, L Swanson, P Antreasian, J Cerna, E Church, M Coltrin, K Johnson, M Lefevre, H Ma, C Mario, C May, M Schmitzer, T Swindle, DP Munoz

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

JOURNAL OF ASTRONOMICAL TELESCOPES INSTRUMENTS AND SYSTEMS 5 (2019) 34004

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

© 2019 Society of PhotoOptical Instrumentation Engineers (SPIE). Twinkle is an upcoming 0.45-m space-based telescope equipped with a visible and two near-infrared spectrometers covering the spectral range 0.4 to 4.5 μm with a resolving power R 250 (λ &lt; 2.42 μm) and R 60 (λ &gt; 2.42 μm). We explore Twinkle's capabilities for small bodies science and find that, given Twinkle's sensitivity, pointing stability, and spectral range, the mission can observe a large number of small bodies. The sensitivity of Twinkle is calculated and compared to the flux from an object of a given visible magnitude. The number, and brightness, of asteroids and comets that enter Twinkle's field of regard is studied over three time periods of up to a decade. We find that, over a decade, several thousand asteroids enter Twinkle's field of regard with a brightness and nonsidereal rate that will allow Twinkle to characterize them at the instrumentation's native resolution with SNR &gt; 100. Hundreds of comets can also be observed. Therefore, Twinkle offers researchers the opportunity to contribute significantly to the field of Solar System small bodies research.


Shape of (101955) Bennu indicative of a rubble pile with internal stiffness

Nature Geoscience Nature Research 12 (2019) 247-252

OS Barnouin, MG Daly, MMA Asad, JH Roberts, ME Perry, HCM Susorney, EB Bierhaus, JA Seabrook, RC Espiritu, AH Nair, L Nguyen, CM Ernst, CD Adam, MC Moreau, CD D'Aubigny, ER Jawin, KJ Walsh, SR Schwartz, R-L Ballouz, N Hirata, N Hirata, S Watanabe, KN Burke, CA Bennett, OSIRIS-REx Team

The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity and prominent surface boulders suggest that it is a rubble pile. High-standing, north–south ridges that extend from pole to pole, many long grooves and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin, which led to its current shape. Today, Bennu might follow a different evolutionary pathway, with an interior stiffness that permits surface cracking and mass wasting.


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, B Kennedy, A Knight, N Martinez-Vlasoff, N Mastrodemos, T McElrath, W Owen, R Park, B Rush, L Swanson, Y Takahashi, D Velez, K Yetter, 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, JL Bandfield, K-M Aye, 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. <br></br> 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.<br></br> 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.


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

Nature Communications Springer Nature 10 (2019) 1291

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

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 (&lt;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

SPACE SCIENCE REVIEWS 215 (2019) UNSP 12

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


The unexpected surface of asteroid (101955) Bennu

Nature Springer Nature 568 (2019) 55-60

DS Lauretta, DN Dellagiustina, 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, MC Nolan, B Rizk, HL Roper, DJ Scheeres, PH Smith, KJ Walsh, CWV Wolner, N Bowles

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 &lt; 2.42 μm; R ~ 60, λ &gt; 2.42 μm) could be obtained with signal-to-noise ratio (SNR) of &gt; 100 with exposure times of &lt;300 s. For other targets (e.g., Phobos), an SNR &gt; 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 &gt; 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, R Garland, S Calcutt, 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).

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