K. H. Baines

University of Wisconsin–Madison, Madison, Wisconsin, United States

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Publications (422)776.38 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ~330% rigid corotation from near ~01 h LT toward ~08 h LT. We suggest these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm, and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.
    Geophysical Research Letters. 05/2014;
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    ABSTRACT: Cassini/VIMS T85 observations of Titan’s north pole show significant specular return from parts of Punga Mare consistent with 6°-slope waves.
    02/2014;
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    ABSTRACT: The Cassini Solstice Mission provides an opportunity to witness the seasonal evolution of Titan’s organic seas and their relationships with lakes and evaporite candidates in the southern and northern hemisphere.
    01/2014;
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    ABSTRACT: Saturn's icy satellites and ring particle surfaces have long been known to be composed mostly of frozen water. However, all surfaces show an absorption due to a non-water-ice component whose identity has not been well understood. In the near infrared, water ice has strong absorptions which limit detectability of other trace components. Similarly, at wavelengths less than about 0.18 microns, water is very absorbing. However, in the ~0.2 to ~1 micron range, water ice has low absorption and trace components are readily detected. Classical interpretations of the UV absorber and dark material on outer Solar System satellites have been varying amounts of tholins and carbon. However, tholins have spectral structure not seen in the icy spectra in the Saturn System. Many silicates also have UV spectral structure that reject them from contributing significantly to the observed spectral signatures. We have constructed a new UV spectrometer and a new environment chamber for studying the spectral properties of materials from 0.1 to 15 microns. In our survey of the spectral properties of materials so far, we find that small amounts of metallic iron and iron oxides in the icy surfaces are compatible with and can explain the UV, visible and near-infrared spectra of icy surfaces in the Saturn system (0.12 to 5.1 microns) using data from the Cassini UltraViolet Imaging Spectrograph (UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS). The wide range of observed UV-NIR (0.1-5 micron) spectral signatures provide strong constraints on composition and grain size distribution, including grain sizes of the ice. Spectra of the Saturnian rings and icy satellites indicate they have a large range of ice grain sizes, from tens of microns to sub-micron. Sub-micron ice grains create unusual spectral properties, which are seen in the spectra of the rings and satellites of Saturn and on satellites further out in the Solar System. Clark et al. (2012, Icarus v218, p831) showed that VIMS spectra were explained by combinations ! of water ice, CO2, nano-sized grains of metallic iron and iron oxide and trace amounts of other compounds. The new UV lab data are providing further evidence for this interpretation and placing further constraints on grain size distributions and abundances of the components.
    AGU Fall Meeting Abstracts. 12/2013;
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    ABSTRACT: A Cassini VIMS spectrum of an active location along Baghdad Sulchus is best fit by a fissure 9 m wide at T=197 K (Goguen et al. 2013, Icarus, accepted). We show that narrower and hotter fissures are unstable due to the exponential increase of the vapor pressure of ice for T greater than 200 K. Ice at 230 K will erode 1 meter/day due to sublimation, so a narrower and warmer fissure will quickly erode to meter widths. The same strong T dependence of the vapor pressure also means that wider fissures at T ~180 K cannot supply to total mass loss rate constraint from Cassini UVIS occultation data. The mass loss rate can be supplied if a significant fraction 190 km) of the total length of the fissures is active as a 9 m wide fissure with T=197 K. The contribution of this hottest component of the fissure emission contributes only a small fraction of the total observed radiated power from the fissures which is dominated by much larger areas at lower T and is best characterized using the CIRS instrument. Copyright 2013 California Institute of Technology.
    10/2013;
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    ABSTRACT: Saturn’s atmospheric responses to seasonal and non-seasonal energy inputs, ranging from change in solar insolation to localized disturbances, have led to discoveries of a warm south polar region/hot south polar vortex (SPV) (Orton and Yanamandra-Fisher, 2005, Science, 307) and low-latitude oscillations (Orton et al., Nature, 453). We now report on our current study of the evolution of a Saturnian season by the characterization of global large-scale variability of temperatures, clouds and local short-scale variability of discrete, episodic events, such as storms and vortices in Saturn’s atmosphere. We will present results on the emerging taxonomy of 5.1-micron hot spots, their variability and correlation with the visible cloud field; and the atmospheric response to rapid episodic changes, followed by the gradual relaxation of the perturbed atmosphere to its equilibrium state in terms of physical parameters. Our study utilizes ground-based mid- and near-infrared observations spanning at least half a Saturnian year (approximately 15 years), acquired at the NASA/InfraRed Telescope Facility (IRTF) and Cassini/near-infrared (VIMS) data in the overlapping time period of 2005 - 2011.
    10/2013;
  • M. L. Delitsky, K. H. Baines
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    ABSTRACT: The energetic lightning storms in the Saturn atmosphere will dissociate molecules into atoms, ions and plasma. Specifically, methane will be dissociated into elemental carbon, most probably in an amorphous form, such as fluffy turbostratic carbon or irregular soot particles. Once formed, this non-crystalline carbon sinks down through the atmosphere reaching an altitude of similar density. Amorphous carbon is converted to graphite under pressure. Graphite has a density of ~2.2 g/cc at room temperature. The density of diamond is ~3.3 g/cc at STP. However, at much higher pressures, the density of diamond increases dramatically, up to 9 grams/cm3 at P=1500 GPa (15 Mbar). As carbon descends through the atmosphere, amorphous carbon becomes graphite which then is converted into diamond, creating various strata of carbon allotropes according to their densities. Densities of the planets increase with depth. Eventually, at great depths, diamond will melt, forming liquid diamond. The melting point of diamond varies with pressure, reaching a high of ~ 8000 K at 500 GPa (5 Mbar). Using updated adiabats and equation-of-state data from Nettelmann et al. (2011), we determined the altitude at which diamond reaches its melting point on each planet. Combining these adiabats with new data for the carbon phase diagram from high-pressure shockwave experiments indicates that diamond may be a stable layer in the atmospheres of Jupiter and Saturn. Previously, only Uranus and Neptune were thought to have conditions in their interiors that would allow the formation of diamond at their cores. It appears that the interior of Jupiter gets hot enough to reach the liquid diamond region of the carbon phase diagram, whereas the interior of Saturn includes regions of temperature and pressure where carbon could exist as solid diamond. At the boundaries (locations of sharp increases in density) on Jupiter and Saturn, there may be diamond rain or diamond oceans sitting as a layer. However, in Uranus and Neptune, the temperatures never reach as high as 8000 K. The cores are ~5000K, too cold for diamond to melt on these planets. Therefore, it appears that diamonds are forever on Uranus and Neptune but not on Jupiter and Saturn.
    10/2013;
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    ABSTRACT: The opposition surge is the huge increase in brightness that is exhibited by nearly every planetary surface as it becomes fully illuminated to an observer. The classic explanation of the surge is that mutual shadows cast by particles in the regolith rapidly disappear as the body approaches a solar phase angle of zero. Additional optical effects such as coherent backscatter or a sharply peaked particle phase function may add to the effect, particularly at solar phase angles less than one degree. The quantitative modeling of the surge yields important information about the compaction state of the surface and particle sizes, which in turn offers clues to the geophysical processes at work on the surface. The study of the opposition surge has centered mainly on visible radiation. Spacecraft observations offer a window into new wavelengths that enable greater understanding of the mechanisms of the surge as well as the physical nature of the surface itself. The Cassini Visual Infrared Mapping Spectrometer gathered measurements of the solar phase curves of the icy moons of Saturn - Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus - throughout the wavelength range of 0.35-5.1 microns and through a full excursion in solar phase angles. This entire spectral range is free of contamination by thermal emission. We find that the nature of the curve changes dramatically longward of the water-ice absorption band at three microns. We attribute this effect to the disappearance of multiple scattering at this wavelength, where the albedo of the moons is low. Without the confounding effect of multiply scattered photons, the compaction state of the surface can be directly measured at this wavelength. We find the derived porosities to be ~95%, similar to lightly packed terrestrial snow. An alternative explanation of the change may be the “disappearance” of small particles that cannot be detected at wavelengths a few times larger than their size. Funded by NASA
    10/2013;
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    ABSTRACT: Saturn's Great Storm of 2010-2011 was a major convective eruption that lofted deep atmospheric aerosols up to the visible cloud tops, providing a rare view of normally hidden materials produced at great depths. These materials produce absorption near 3 microns, which is not seen on Saturn outside of storm regions. We used near-infrared spectra of the storm, obtained by the Visual and Infrared Mapping Spectrometer on the Cassini orbiter, to constrain the composition of the cloud particles. We found compelling evidence that the storm cloud contains a multi-component aerosol population comprised primarily of ammonia ice, with water ice the best-defined secondary component. The most likely third component is ammonium hydrosulfide or some weakly absorbing material similar to what dominates visible clouds outside the storm region. Horizontally heterogeneous cloud models favor ammonium hydrosulfide as the third component, while horizontally uniform models favor the weak absorber. Both models rely on water ice absorption to compensate for residual spectral gradients produced by ammonia ice from 3.0 microns to 3.1 microns and need the relatively conservative third component to fill in the sharp ammonia ice absorption peak near 2.96 microns. The best heterogeneous model has spatial coverage fractions of 55% ammonia ice, 22% water ice, and 23% ammonium hydrosulfide. The best homogeneous model has an optically thin layer of weakly absorbing particles above an optically thick layer of water ice particles coated by ammonia ice. These Cassini data provide the first spectroscopic evidence of water ice in Saturn's atmosphere. The presence of water ice in this major storm supports the hypothesis that these convective storms are powered by condensation of water and originate in the 10-20 bar depths of Saturn. This research was supported by NASA's Outer Planets Research Program under grant NNX11AM58G.
    10/2013;
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    ABSTRACT: Cassini has been orbiting Saturn for over nine years. During this epoch, the ring shadow has moved from covering a relatively large portion of the northern hemisphere to covering a large swath south of the equator and continues to move southward. At Saturn Orbit Insertion in 2004, the ring plane was inclined by ~24 degrees relative to the Sun-Saturn vector. The projection of the B-ring onto Saturn reached as far as 40N along the central meridian 52N at the terminator). At its maximum extent, the ring shadow can reach as far as 48N/S 58N/S at the terminator). The net effect is that the intensity of both ultraviolet and visible sunlight penetrating into any particular latitude will vary depending on both Saturn’s axis relative to the Sun and the optical thickness of each ring system. In essence, the rings act like venetian blinds. Our previous work [1] examined the variation of the solar flux as a function of solar inclination, i.e. ~8 year season at Saturn. Here, we report on the impact of the oscillating ring shadow on the photolysis and production rates of hydrocarbons in Saturn’s stratosphere and upper troposphere, including acetylene, ethane, propane, and benzene. Beginning with methane, we investigate the impact on production and loss rates of the long-lived photochemical products leading to haze formation are examined at several latitudes over a Saturn year. Similarly, we assess its impact on phosphine abundance, a disequilibrium species whose presence in the upper troposphere is a tracer of convection processes in the deep atmosphere. Comparison to the corresponding rates for the clear atmosphere and for the case of Jupiter, where the variation of solar insolation due to tilt is known to be insignificant 3 degree inclination), will be presented. We will present our ongoing analysis of Cassini’s CIRS, UVIS, and VIMS datasets that provide an estimate of the evolving haze content of the northern hemisphere and we will begin to assess the implications for dynamical mixing. [1] Edgington, S.G., et al., 2012. Photochemistry in Saturn’s Ring Shadowed Atmosphere: Modeling, Observations, and Preliminary Analysis. Bull. American. Astron. Soc., 38, 499 (#11.23).
    10/2013;
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    ABSTRACT: On T85 Cassini VIMS observed a spectacular specular reflection of the Sun off Titan's Kivu Lacus (87.5N). This sunglint was so bright that it was observable not just at 5 microns, but also within the 2.7/2.8 and 2.0 micron windows as well. Because the specular reflectivity off of methane/ethane liquid is independent of wavelength in the VIMS range, the specular reflection allows us to infer Titan's atmospheric transmission spectrum. We will discuss the results of our opacity analysis with regard to Titan's atmospheric absorption and scattering. Empirical knowledge of the normal optical depth will directly enable us to disentangle surface from atmospheric effects, with the eventual goal of generating of absolute surface albedo spectra. This novel technique complements existing methods, occultations and radiative transfer analyses, and will enable identification of changes to Titan's polar atmosphere through the end of the Cassini mission.
    10/2013;
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    ABSTRACT: We present well-calibrated, high-resolution maps of Saturn's thermal emission at 2.2-cm wavelength obtained by the Cassini RADAR radiometer through the Prime and Equinox Cassini missions, a period covering approximately 6 years. The absolute brightness temperature calibration of 2% achieved is more than twice better than for all previous microwave observations reported for Saturn, and the spatial resolution and sensitivity achieved each represent nearly an order of magnitude improvement. The brightness temperature of Saturn in the microwave region depends on the distribution of ammonia, which our radiative transfer modeling shows is the only significant source of absorption in Saturn's atmosphere at 2.2-cm wavelength. At this wavelength the thermal emission comes from just below and within the ammonia cloud-forming region, and yields information about atmospheric circulations and ammonia cloud-forming processes. The maps are presented as residuals compared to a fully saturated model atmosphere in hydrostatic equilibrium. Bright regions in these maps are readily interpreted as due to depletion of ammonia vapor in, and, for very bright regions, below the ammonia saturation region. Features seen include the following: a narrow equatorial band near full saturation surrounded by bands out to about 10° planetographic latitude that demonstrate highly variable ammonia depletion in longitude; narrow bands of depletion at ‑35° latitude; occasional large oval features with depleted ammonia around ‑45° latitude; and the 2010–2011 storm, with extensive saturated and depleted areas as it stretched halfway around the planet in the northern hemisphere. Comparison of the maps over time indicates a high degree of stability outside a few latitudes that contain active regions.
    Icarus 09/2013; 226(1):522-535. · 3.16 Impact Factor
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    ABSTRACT: During April and May 2013 there was a large and unprecedented co-ordinated campaign of observations using observatoins of Saturn's aurora, using Cassini instruments, the Cassini spacecraft, the Hubble Space Telescope, Keck telescope, NASA IRTF and the Very Large Telescope. Here, we present the analysis of the Cassini VIMS and UVIS observations obtained during this period that were simultenous in space and time, enabling the study of the energy balance of the upper atmosphere of Saturn. We cross-correlate the properties of H3+ derived from Cassini VIMS observations to those derived using Keck NIRSPEC observations.
    09/2013;
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    ABSTRACT: A global-scale interaction between Saturn's ionosphere and ring system was found in April 2011, during Saturn's northern hemisphere spring using the 10-metre Keck telescope[1]. Saturn's ionosphere is produced when the otherwise charge-neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low-latitudes the latter should result in a weak planet-wide glow in infrared, corresponding to the planets uniform illumination by the Sun. The observed low-latitude ionospheric electron density is lower and temperature is higher than predicted by models. A planet-ring magnetic connection has been previously suggested in which an influx of water from the rings could explain the lower than expected electron densities in Saturn's atmosphere. We reported the detection of a pattern of features, unexpected in the ionosphere, extending across a broad latitude band between 25-55 degrees that is superposed on the lower latitude background glow, with peaks in emission that map along the planet's magnetic field lines to features in Saturn's rings. This pattern implied the transfer of charged particles from the ring-plane to the ionosphere. This transport may be responsible for the low electron densities found in specific locations. Here we examine a new dataset from 2013 which have far superior signal to noise, owing to 5 times more spectral data. Saturn's northern hemisphere is tilted ~10 degrees more towards us than before, leading to better spatial resolution of the ionosphere and so a better look at its modulation by ring water influx.
    09/2013;
  • L. A. Sromovsky, K. H. Baines, P. M. Fry
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    ABSTRACT: Our analysis of Cassini/VIMS near-infrared spectra of Saturn's Great Storm of 2010–2011 reveals a multi-component aerosol composition comprised primarily of ammonia ice, with a significant component of water ice. The most likely third component is ammonium hydrosulfide or some weakly absorbing material similar to what dominates visible clouds outside the storm region. Horizontally heterogeneous models favor ammonium hydrosulfide as the third component, while horizontally uniform models favor the weak absorber. Both models rely on water ice absorption to compensate for residual spectral gradients produced by ammonia ice from 3.0 μm to 3.1 μm and need the third component to fill in the sharp ammonia ice absorption peak near 2.96 μm. The best heterogeneous model has spatial coverage fractions of 55% ammonia ice, 22% water ice, and 23% ammonium hydrosulfide. The best homogeneous model has an optically thin layer of weakly absorbing particles above an optically thick layer of water ice particles coated by ammonia ice. This is the first spectroscopic evidence of water ice in Saturn's atmosphere, found near the level of Saturn's visible cloud deck where it could only be delivered by powerful convection originating from ˜200 km deeper in the atmosphere.
    Icarus 09/2013; 226(1):402-418. · 3.16 Impact Factor
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    ABSTRACT: Saturn's moon Enceladus emits a plume of water vapour and micrometre-sized ice particles from a series of warm fissures located near its south pole. This geological activity could be powered or controlled by variations in the tidal stresses experienced by Enceladus as it moves around its slightly eccentric orbit. The specific mechanisms by which these varying stresses are converted into heat, however, are still being debated. Furthermore, it has proved difficult to find a clear correlation between the predicted tidal forces and measured temporal variations in the plume's gas content or the particle flux from individual sources. Here we report that the plume's horizontally integrated brightness is several times greater when Enceladus is near the point in its eccentric orbit where it is furthest from Saturn (apocentre) than it is when near the point of closest approach to the planet (pericentre). More material therefore seems to be escaping from beneath Enceladus' surface at times when geophysical models predict its fissures should be under tension and therefore may be wider open.
    Nature 07/2013; · 38.60 Impact Factor
  • Source
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    ABSTRACT: Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities.
    Nature 04/2013; 496(7444):193-5. · 38.60 Impact Factor
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    ABSTRACT: Titan's surface seems to behave as a Lambertian body at first order. We now try to refine its photometric function by testing several empirical photometry laws.
    03/2013;
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    ABSTRACT: Cassini has been orbiting Saturn for over eight years. During this epoch, the ring shadow has moved from shading a large portion of the northern hemisphere (the ring plane was inclined by 24 degrees relative to the Sun-Saturn vector) to shading mid-latitudes south of the equator and continues southward. At its maximum extent, the projection of the ring plane shadow onto Saturn can reach as far as 48N ( 58N at the terminator). The net result, is that the intensity of both ultraviolet and visible sunlight penetrating onto any particular northern/southern latitude will vary depending on Saturn’s tilt relative to the Sun and the optical thickness of each ring system. Our previous work has examined the variation of the solar flux as a function of solar inclination, i.e. season on Saturn. Here we report on the impact of the oscillating ring shadow on the photolysis and production rates of key hydrocarbons in Saturn’s stratosphere and upper troposphere, including ethane, acetylene, propane, benzene. We investigate the impact on production and loss rates of the long-lived, photochemical hydrocarbons leading to haze formation at several latitudes over one Saturn year. Similarly, we assess the impact on the abundance of phosphine, a disequilibrium species whose presence in the upper troposphere is a tracer of convection processes in the deep atmosphere. Along with the above, we present preliminary analysis of Cassini’s UVIS and VIMS datasets that provide an estimate of the evolving haze content of the northern hemisphere. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
    10/2012;
  • M. L. Delitsky, K. H. Baines
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    ABSTRACT: Observations by many spacecraft that have visited Venus over the last 40 years appear to confirm the presence of lightning storms in the Venus atmosphere. Recent observations by Venus Express indicate that lightning frequency and power is similar to that on Earth. While storms are occurring, energy deposition by lightning into Venus atmospheric constituents will immediately dissociate molecules into atoms, ions and plasma from the high temperatures in the lightning column (>30,000 K) and the associated shock waves and heating, after which these atom and ion fragments will recombine during cooldown to form new sets of molecules. Lightning will re-sort the atoms of C,O,S,N,H to create highly energetic new products. Spark and discharge experiments in the literature suggest that lightning effects on the main atmospheric molecules CO2, N2, SO2, H2SO4 and H2O will yield new molecules such as mixed carbon oxides (CnOm), mixed sulfur oxides (SnOm), oxygen (O2), elemental sulfur (Sn), nitrogen oxides (NO, N2O, NO2, NO3), sulfuric acid clusters (HnSmOx-.aHnSmOx e.g. HSO4-.mH2SO4), polysulfur oxides, carbon soot, and also halogen oxides from HCl or HF and other exotic species. Many of these molecular species may be detectable by instruments onboard Venus Express. We explore the diversity of new products likely created in the storm clouds on Venus.
    10/2012;

Publication Stats

2k Citations
776.38 Total Impact Points

Institutions

  • 2002–2014
    • University of Wisconsin–Madison
      • Space Sciences and Engineering Center
      Madison, Wisconsin, United States
  • 2013
    • University of Leicester
      • Department of Physics and Astronomy
      Leicester, ENG, United Kingdom
  • 1991–2013
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2011
    • University of Oxford
      • Department of Physics
      Oxford, England, United Kingdom
  • 2010
    • University of Nantes
      • Laboratoire de Planétologie et Géodynamique de Nantes (LPG)
      Nantes, Pays de la Loire, France
  • 2009
    • United States Geological Survey
      Reston, Virginia, United States
    • Laboratoire d'Etudes en Géophysique et Óceanographie Spatiales
      Tolosa de Llenguadoc, Midi-Pyrénées, France
  • 2007–2009
    • The University of Arizona
      • Department of Planetary Sciences
      Tucson, AZ, United States
    • Cornell University
      • Department of Astronomy
      Ithaca, NY, United States
  • 2005
    • Université Paris-Sud 11
      • Institut d'Astrophysique Spatiale
      Paris, Ile-de-France, France
  • 2000–2001
    • University of Louisville
      Louisville, Kentucky, United States
  • 1998
    • The University of Edinburgh
      Edinburgh, Scotland, United Kingdom
  • 1993
    • University of Colorado
      Denver, Colorado, United States
  • 1988–1989
    • Washington University in St. Louis
      San Luis, Missouri, United States