Publications


Evidence for H2 dissociation and recombination heat transport in the atmosphere of KELT-9b

Astrophysical Journal Letters American Astronomical Society 888 (2020) L15

M Mansfield, JL Bean, KB Stevenson, TD Komacek, TJ Bell, X Tan, M Malik, TG Beatty, I Wong, NB Cowan, L Dang, J-M Désert, JJ Fortney, BS Gaudi, D Keating, L Kreidberg, EM-R Kempton, V Parmentier, KG Stassun


Stormy water on Mars: the distribution and saturation of atmospheric water during the dusty season

Science American Association for the Advancement of Science (2020)

AA Fedorova, F Montmessin, O Korablev, M Luginin, A Trokhimovskiy, DA Belyaev, NI Ignatiev, F Lefèvre, J Alday, P Irwin, K Olsen, J-L Bertaux, E Millour, A Määttänen, A Shakun, AV Grigoriev, A Patrakeev, S Korsa, N Kokonkov, L Baggio, F Forget, C Wilson

The loss of water from Mars to space is thought to result from the transport of water to the upper atmosphere, where it is dissociated to hydrogen and escapes the planet. Recent observations have suggested large, rapid seasonal intrusions of water into the upper atmosphere, boosting the hydrogen abundance. We use the Atmospheric Chemistry Suite on the ExoMars Trace Gas Orbiter to characterize the water distribution by altitude. Water profiles during the 2018–2019 southern spring and summer stormy seasons show that high-altitude water is preferentially supplied close to perihelion, and supersaturation occurs even when clouds are present. This implies that the potential for water to escape from Mars is higher than previously thought.


Ice, Fire, or Fizzle: The Climate Footprint of Earth's Supercontinental Cycles

Geochemistry, Geophysics, Geosystems (2020)

R PIERREHUMBERT, A Lenardic, M Jellinek


Venus III The View After Venus Express

Springer, 2020

B Bézard, C Russell, T Satoh, S Smrekar, C Wilson

The ten papers in this book, written by an international team of specialists, are the products of this effort.


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

Planetary and Space Science Elsevier (2020)

T WARREN, E Sefton-Nash, R Fisackerly, R Trautner, O King, N BOWLES


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


Initial results from the InSight mission on Mars

Nature Geoscience Springer Science and Business Media LLC (2020)

N Warner, N Teanby, J Tromp, M van Driel, CL Johnson, P Lognonné, M Golombek, A Spiga, T Spohn, SC Stähler, C Perrin, D Antonangeli, S Asmar, C Beghein, N Bowles, P Chi, U Christensen, E Bozdag, GS Collins, I Daubar, J Clinton, V Dehant, M Fillingim, W Folkner, J Garvin


Exoplanetary Monte Carlo radiative transfer with correlated-k I. Benchmarking transit and emission observables

Monthly Notices of the Royal Astronomical Society Oxford University Press 487 (2019) 2082-2096

G Lee, SL Grimm, J Taylor, J-L Baudino, R Garland, PGJ Irwin, K Wood

Current observational data of exoplanets are providing increasing detail of their 3D atmospheric structures. As characterisation efforts expand in scope, the need to develop consistent 3D radiative-transfer methods becomes more pertinent as the complex atmospheric properties of exoplanets are required to be modelled together consistently. We aim to compare the transmission and emission spectra results of a 3D Monte Carlo Radiative Transfer (MCRT) model to contemporary radiative-transfer suites. We perform several benchmarking tests of a MCRT code, Cloudy Monte Carlo Radiative Transfer (CMCRT), to transmission and emission spectra model output. We add flexibility to the model through the use of k-distribution tables as input opacities. We present a hybrid MCRT and ray tracing methodology for the calculation of transmission spectra with a multiple scattering component. CMCRT compares well to the transmission spectra benchmarks at the 10s of ppm level. Emission spectra benchmarks are consistent to within 10% of the 1D models. We suggest that differences in the benchmark results are likely caused by geometric effects between plane-parallel and spherical models. In a practical application, we post-process a cloudy 3DHD 189733b GCM model and compare to available observational data. Our results suggest the core methodology and algorithms of CMCRT produce consistent results to contemporary radiative transfer suites. 3D MCRT methods are highly suitable for detailed post-processing of cloudy and non-cloudy 1D and 3D exoplanet atmosphere simulations in instances where atmospheric inhomogeneities, significant limb effects/geometry or multiple scattering components are important considerations.


The atmospheric circulation of ultra-hot Jupiters

Astrophysical Journal American Astronomical Society 886 (2019) 1-20

X Tan, T Komacek


The Snowball Stratosphere

Journal of Geophysical Research: Atmospheres 124 (2019) 11819-11836

DS Abbot, TA Shaw, RJ Graham

©2019. American Geophysical Union. All Rights Reserved. According to the Snowball Earth hypothesis, Earth has experienced periods of low-latitude glaciation in its deep past. Prior studies have used general circulation models (GCMs) to examine the effects such an extreme climate state might have on the structure and dynamics of Earth's troposphere, but the behavior of the stratosphere has not been studied in detail. Understanding the snowball stratosphere is important for developing an accurate account of the Earth's radiative and chemical properties during these episodes. Here we conduct the first analysis of the stratospheric circulation of the Snowball Earth using ECHAM6 general circulation model simulations. In order to understand the factors contributing to the stratospheric circulation, we extend the Statistical Transformed Eulerian Mean framework. We find that the stratosphere during a snowball with prescribed modern ozone levels exhibits a weaker meridional overturning circulation, reduced wave activity, and stronger zonal jets and is extremely cold relative to modern conditions. Notably, the snowball stratosphere displays no sudden stratospheric warmings. Without ozone, the stratosphere displays a complete lack of polar vortex and even colder temperatures. We also explicitly quantify for the first time the cross-tropopause mass exchange rate and stratospheric mixing efficiency during the snowball and show that our values do not change the constraints on CO2 inferred from geochemical proxies during the Marinoan glaciation (ca. 635 Ma), unless the O2 concentration during the snowball was orders of magnitude less than the CO2 concentration.


Oxygen isotopic ratios in Martian water vapour observed by ACS MIR on board the ExoMars Trace Gas Orbiter

Astronomy & Astrophysics EDP Sciences 630 (2019) A91-A91

J Alday, CF Wilson, PGJ Irwin, KS Olsen, L Baggio, F Montmessin, A Trokhimovskiy, O Korablev, AA Fedorova, DA Belyaev, A Grigoriev, A Patrakeev, A Shakun

<jats:p>Oxygen isotope ratios provide important constraints on the history of the Martian volatile system, revealing the impact of several processes that might fractionate them, such as atmospheric loss into space or interaction with the surface. We report infrared measurements of the Martian atmosphere obtained with the mid-infrared channel (MIR) of the Atmospheric Chemistry Suite (ACS), onboard the ExoMars Trace Gas Orbiter. Absorption lines of the three main oxygen isotopologues of water vapour (H <jats:sub>2</jats:sub><jats:sup>16</jats:sup> O, H <jats:sub>2</jats:sub><jats:sup>18</jats:sup> O, and H <jats:sub>2</jats:sub><jats:sup>17</jats:sup> O) observed in the transmission spectra allow, for the first time, the measurement of vertical profiles of the <jats:sup>18</jats:sup>O/<jats:sup>16</jats:sup>O and <jats:sup>17</jats:sup>O/<jats:sup>16</jats:sup>O ratios in atmospheric water vapour. The observed ratios are enriched with respect to Earth-like values (<jats:italic>δ</jats:italic><jats:sup>18</jats:sup>O = 200 ± 80‰ and <jats:italic>δ</jats:italic><jats:sup>17</jats:sup>O = 230 ± 110‰ corresponding to the Vienna Standard Mean Ocean Water). The vertical structure of these ratios does not appear to show significant evidence of altitudinal variations.</jats:p>


There is no Plan B for dealing with the climate crisis

BULLETIN OF THE ATOMIC SCIENTISTS Informa UK Limited 75 (2019) 215-221

R Pierrehumbert

© 2019, © 2019 Bulletin of the Atomic Scientists. To halt global warming, the emission of carbon dioxide into the atmosphere by human activities such as fossil fuel burning, cement production, and deforestation needs to be brought all the way to zero. The longer it takes to do so, the hotter the world will get. Lack of progress towards decarbonization has created justifiable panic about the climate crisis. This has led to an intensified interest in technological climate interventions that involve increasing the reflection of sunlight to space by injecting substances into the stratosphere which lead to the formation of highly reflective particles. When first suggested, such albedo modification schemes were introduced as a “Plan B,” in case the world economy fails to decarbonize, and this scenario has dominated much of the public perception of albedo modification as a savior waiting in the wings to protect the world against massive climate change arising from a failure to decarbonize. But because of the mismatch between the millennial persistence time of carbon dioxide and the sub-decadal persistence of stratospheric particles, albedo modification can never safely play more than a very minor role in the portfolio of solutions. There is simply no substitute for decarbonization.


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


Atmospheric circulation of brown dwarfs and Jupiter- and Saturn-like planets: Zonal jets, long-term variability, and QBO-type oscillations

Astrophysical Journal American Astronomical Society 883 (2019)

AP Showman, X Tan, X Zhang

Brown dwarfs and directly imaged giant planets exhibit significant evidence for active atmospheric circulation, which induces a large-scale patchiness in the cloud structure that evolves significantly over time, as evidenced by infrared light curves and Doppler maps. These observations raise critical questions about the fundamental nature of the circulation, its time variability, and its overall relationship to the circulation on Jupiter and Saturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east–west) jet streams at the cloud level; moreover, both planets exhibit long-term stratospheric oscillations involving perturbations of zonal wind and temperature that propagate downward over time on timescales of ~4 yr (Jupiter) and ~15 yr (Saturn). These oscillations, dubbed the quasi-quadrennial oscillation (QQO) for Jupiter and the semiannual oscillation (SAO) on Saturn, are thought to be analogous to the quasi-biennial oscillation (QBO) on Earth, which is driven by upward propagation of equatorial waves from the troposphere. To investigate these issues, we here present global, three-dimensional, high-resolution numerical simulations of the flow in the stratified atmosphere—overlying the convective interior—of brown dwarfs and Jupiter-like planets. The effect of interior convection is parameterized by inducing small-scale, randomly varying perturbations in the radiative–convective boundary at the base of the model. Radiative damping is represented using an idealized Newtonian cooling scheme. In the simulations, the convective perturbations generate atmospheric waves and turbulence that interact with the rotation to produce numerous zonal jets. Moreover, the equatorial stratosphere exhibits stacked eastward and westward jets that migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian QQO, and Saturnian SAO. This is the first demonstration of a QBO-like phenomenon in 3D numerical simulations of a giant planet.


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.


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 (&lt;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.


Validation of the HITRAN 2016 and GEISA 2015 line lists using ACE-FTS solar occultation observations

Journal of Quantitative Spectroscopy and Radiative Transfer 236 (2019)

KS Olsen, CD Boone, GC Toon, F Montmessin, AA Fedorova, O Korablev, A Trokhimovskiy

© 2019 Elsevier Ltd The ExoMars Trace Gas Orbiter (TGO) began its nominal science phase at Mars in April 2018, following releases of editions to two major spectroscopic line lists: GEISA 2015 (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), and HITRAN 2016 (High Resolution Transmission). This work evaluates both line lists over the spectral region between 2325–4350 cm−1 using terrestrial solar occultation observations made by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). This spectral region is targeted on Mars by two complementary solar occultation instruments on TGO that will monitor temperature and pressure, aerosols, the abundance of CO2, CO, H2O, HDO, CH4, and other undetected trace gases. Major updates to GEISA 2015 and HITRAN 2016, with respect to previous editions, have been focused on CO2 absorption features in support of Earth-observing missions to monitor greenhouse. Since CO2 is the dominant absorber on Mars, making up 96.5% of the atmosphere, validating the updated line lists is critically important before their deployment for ExoMars. We report that updated CO2 parameters make significant improvements to spectral fits made when using both line lists. Several updates to H2O lines in both line lists also show improvement. The primary difference we observe between the two line lists comes from O3 absorption features near 3850 cm−1 and from several CH4 absorption lines in the regions 2800–3200 cm−1 and 4000–4300 cm−1. Because of these differences, we find that using HITRAN 2016 tends to result in better spectral fits, especially below 30 km, than using GEISA 2015 in this spectral region. Differences are strongly reduced with increasing altitude ( > 40 km) as pressure and gas abundance falls off. It was also discovered that several new errors in both new editions of GEISA and HITRAN were introduced since the HITRAN 2012.


The Yamato-type (CY) carbonaceous chondrite group: Analogues for the surface of asteroid Ryugu?

Geochemistry Elsevier 79 (2019) 125531

AJ King, H Bates, D Krietsch, H Busemann, PL Clay, PF Schofield, SS Russell

We report new mineralogical, petrographic and noble gas analyses of the carbonaceous chondrite meteorites Y-82162 (C1/2ung), Y-980115 (CI1), Y-86029 (CI1), Y-86720 (C2ung), Y-86789 (C2ung), and B-7904 (C2ung). Combining our results with literature data we show that these meteorites experienced varying degrees of aqueous alteration followed by short-lived thermal metamorphism at temperatures of &gt;500 °C. These meteorites have similar mineralogy, textures and chemical characteristics suggesting that they are genetically related, and we strongly support the conclusion of Ikeda (1992) that they form a distinct group, the CYs (“Yamato-type”). The CY chondrites have the heaviest oxygen isotopic compositions (δ17O ˜12‰, δ18O ˜22‰) of any meteorite group, high abundances of Fe-sulphides (˜10 ‒ 30 vol%) and phosphates, and contain large grains of periclase and unusual objects of secondary minerals not reported in other carbonaceous chondrites. These features cannot be attributed to parent body processes alone, and indicate that the CYs had a different starting mineralogy and/or alteration history to other chondrite groups, perhaps because they formed in a different region of the protoplanetary disk. The short cosmic-ray exposure ages (≤1.3 Ma) of the CY chondrites suggest that they are derived from a near-Earth source, with recent observations by the Hayabusa2 spacecraft highlighting a possible link to the rubble-pile asteroid Ryugu.


Investigating the semiannual oscillation on Mars using data assimilation

Icarus Elsevier 333 (2019) 404-414 )

T Ruan, N Lewis, S Lewis, L Montabone, P Read

A Martian semiannual oscillation (SAO), similar to that in the Earths tropical stratosphere, is evident in the Mars Analysis Correction Data Assimilation reanalysis dataset (MACDA) version 1.0, not only in the tropics, but also extending to higher latitudes. Unlike on Earth, the Martian SAO is found not always to reverse its zonal wind direction, but only manifests itself as a deceleration of the dominant wind at certain pressure levels and latitudes. Singular System Analysis (SSA) is further applied on the zonal-mean zonal wind in different latitude bands to reveal the characteristics of SAO phenomena at different latitudes. The second pair of principal components (PCs) is usually dominated by a SAO signal, though the SAO signal can be strong enough to manifest itself also in the first pair of PCs. An analysis of terms in the Transformed Eulerian Mean equation (TEM) is applied in the tropics to further elucidate the forcing processes driving the tendency of the zonal-mean zonal wind. The zonal-mean meridional advection is found to correlate strongly with the observed oscillations of zonal-mean zonal wind, and supplies the majority of the westward (retrograde) forcing in the SAO cycle. The forcing due to various non-zonal waves supplies forcing to the zonal-mean zonal wind that is nearly the opposite of the forcing due to meridional advection above ∼3 Pa altitude, but it also partly supports the SAO between 40 Pa and 3 Pa. Some distinctive features occurring during the period of the Mars year (MY) 25 global-scale dust storm (GDS) are also notable in our diagnostic results with substantially stronger values of eastward and westward momentum in the second half of MY 25 and stronger forcing due to vertical advection, transient waves and thermal tides


Towards the analysis of JWST exoplanet spectra: the effective temperature in the context of direct imaging

Monthly Notices of the Royal Astronomical Society Oxford University Press 490 (2019) 2086-2090

R Garland, J-L Baudino, J Taylor, P Irwin

The current sparse wavelength range coverage of exoplanet direct imaging observations, and the fact that models are defined using a finite wavelength range, lead both to uncertainties on effective temperature determination. We study these effects using blackbodies and atmospheric models and we detail how to infer this parameter. Through highlighting the key wavelength coverage that allows for a more accurate representation of the effective temperature, our analysis can be used to mitigate or manage extra uncertainties being added in the analysis from the models. We find that the wavelength range coverage will soon no longer be a problem. An effective temperature computed by integrating the spectroscopic observations of the James Webb Space Telescope will give uncertainties similar to, or better than, the current state–of–the–art, which is to fit models to data. Accurately calculating the effective temperature will help to improve current modelling approaches. Obtaining an independent and precise estimation of this crucial parameter will help the benchmarking process to identify the best practice to model exoplanet atmospheres.

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