W. D. Smythe

University of Nantes, Naoned, Pays de la Loire, France

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Publications (179)313.95 Total impact

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    ABSTRACT: The origin of Titan's atmospheric methane and of the volatiles measured in Enceladus' south pole plumes remain, to this day, unresolved. Clathrate hydrates are among the favored deep-seated reservoir candidates. However, the conditions allowing for their dissociation and the release of volatiles to the atmosphere (Titan) or the plumes (Enceladus) are still poorly constrained. This is mainly because there is a lack of knowledge on the stability of mixed clathrate hydrates in presence of anti-freeze agents such as ammonia. We present a new high-pressure system, a high-pressure cryogenic calorimeter, currently being developed at JPL that is designed to address this deficiency in the literature. We use a liquid nitrogen - cooled Setaram BT2.15 calorimeter, located at the Ice Physics Laboratory, JPL (see Figure 1). The temperature range achievable with this instrument is 77-473 K. This calorimeter uses Calvet elements (3D arrays of thermocouples), to measure the heat flux required to follow a predefined heating rate within a sample and a reference cell with a resolution of 0.1 μW. A high-pressure system is being implemented in order to develop the capability of investigating the pressure range 0-100 bars. This system includes: high-pressure cells with a gas flow system (from Setaram), a gas handling system to deliver the gas from 1K bottles of CH4, CO2, and N2, a vacuum system, and a vent system. With the calorimeter, clathrate hydrates will be synthesized within the cells from an H2O-NH3 aqueous solution. Then, cooling and heating tests will be conducted for several gas pressures in order to measure simultaneously the dissociation curve and thermodynamic properties (heat capacity, latent heat). Similarly, clathrate hydrates will be synthesized from the solution of interest within the fluid pressure cell. Dissociation curves will be measured by varying temperature, and following optically and via Raman and diffuse reflectance infrared spectroscopy the samples' evolution. We are nearing the end of the development phase for both apparatus, and will present preliminary tests and results at the meeting. This work has been conducted at the Jet Propulsion Laboratory, California, Institute of Technology, under contract to NASA.
    Full-text · Article · Dec 2011
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    ABSTRACT: At the request of the Satellites Panel of the National Research Council (NRC) Planetary Science Decadal Survey, a Rapid Mission Architecture (RMA) study of possible missions to Saturn's moon Enceladus was conducted at the Jet Propulsion Laboratory in January and February of 2010. This was one of many studies commissioned by this NRC Decadal Survey. In this study, 15 Enceladus mission architectures were examined that spanned a broad range of potential science return and total estimated mission cost.
    No preview · Conference Paper · Apr 2011
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    ABSTRACT: A study conducted in April 2010 for the 2012 Planetary Science Decadal Survey's Giant Planets Panel addressed the "Saturn Ring Observer" concept, a mission that would perform detailed, close-up observations of Saturn's rings. There were two study objectives: 1) investigate the method(s) by which such a spacecraft might be placed in a tight circular orbit around Saturn, using chemical or nuclear-electric propulsion or aerocapture in Saturn's atmosphere; and 2) identify technological developments for the next decade that would enable such a mission in the post-2023 time frame (after the next saturnian equinox), with a particular focus on power and propulsion. The "tight circular orbit" is a non-Keplerian orbit displaced 2-3 km perpendicular to the mean ring plane. A spacecraft in such an orbit would appear to "hover" over the ring particles orbiting Saturn directly "beneath" it, so the study team dubbed this the "hover orbit." Operations technologies were found to be important drivers so they were examined also. The extreme delta-V budgets (for then-known trajectories) of previous mission implementation studies made chemical propulsion implementations impractical, so they used nuclear electric propulsion (NEP) or aerocapture. The new study identified types of trajectories that would deliver a spacecraft from Saturn approach to hover orbit initiation for ∼3.5 km/s delta-V, within reach of a single chemical bipropellant stage and, for some mission concepts, launch on an Atlas launch vehicle. Hover spacecraft designs using chemical engines, radioisotope electric propulsion (REP), and NEP were considered. This type of mission could use REP and possibly NEP of relatively low specific power. This paper summarizes the results of the new study.
    No preview · Article · Jan 2011
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    ABSTRACT: Comet Odyssey is a proposed New Frontiers mission that would return the first samples from the surface of a cometary nucleus. Stardust demonstrated the tremendous power of analysis of returned samples in terrestrial laboratories versus what can be accomplished in situ with robotic missions. But Stardust collected only 1 milligram of coma dust, and the 6.1 km/s flyby speed heated samples up to 2000 K. Comet Odyssey would collect two independent 800 cc samples directly from the surface in a far more benign manner, preserving the primitive composition. Given a minimum surface density of 0.2 g/cm3, this would return two 160 g surface samples to Earth. Comet Odyssey employs solar-electric propulsion to rendezvous with the target comet. After 180 days of reconnaissance and site selection, the spacecraft performs a "touch-and-go'' maneuver with surface contact lasting 3 seconds. A brush-wheel sampler on a remote arm collects up to 800 cc of sample. A duplicate second arm and sampler collects the second sample. The samples are placed in a return capsule and maintained at colder than -70 C during the return flight and at colder than -30 C during re-entry and for up to six hours after landing. The entire capsule is then refrigerated and transported to the Astromaterials Curatorial Facility at NASA/JSC for initial inspection and sample analysis by the Comet Odyssey team. Comet Odyssey's planned target was comet 9P/Tempel 1, with launch in December 2017 and comet arrival in June 2022. After a stay of 300 days at the comet, the spacecraft departs and arrives at Earth in May 2027. Comet Odyssey is a forerunner to a flagship Cryogenic Comet Sample Return mission that would return samples from deep below the nucleus surface, including volatile ices. This work was supported by internal funds from the Jet Propulsion Laboratory.
    No preview · Article · Oct 2010
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    ABSTRACT: A study conducted in April 2010 for the 2012 Planetary Science Decadal Survey's Giant Planets Panel addressed the "Saturn Ring Observer" concept, a mission that would perform detailed, close-up observations of Saturn's rings. There were two study objectives: 1) investigate the method(s) by which such a spacecraft might be placed in a tight circular orbit around Saturn, using chemical or nuclear-electric propulsion or aerocapture in Saturn's atmosphere; and 2) identify technological developments for the next decade that would enable such a mission in the post-2023 time frame (after the next saturnian equinox), with a particular focus on power and propulsion. The "tight circular orbit" is a non-Keplerian orbit displaced 2-3 km perpendicular to the mean ring plane. A spacecraft in such an orbit would appear to "hover" over the ring particles orbiting Saturn directly "beneath" it, so the study team dubbed this the "hover orbit." Operations technologies were found to be important drivers so they were examined also. The extreme delta-V budgets (for then-known trajectories) of previous mission implementation studies made chemical propulsion implementations impractical, so they used nuclear electric propulsion (NEP) or aerocapture. The new study identified types of trajectories that would deliver a spacecraft from Saturn approach to hover orbit initiation for -3.5 km/s delta-V, within reach of a single chemical bipropellant stage and, for some mission concepts, launch on an Atlas launch vehicle. Hover spacecraft designs using chemical engines, radioisotope electric propulsion (REP), and NEP were considered. This type of mission could use REP and possibly NEP of relatively low specific power. This paper summarizes the results of the new study.
    No preview · Article · Sep 2010
  • W. D. Smythe · R. Nelson · M. D. Boryta
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    ABSTRACT: Ammonia has been suggested as a probable source for sustaining Titan's thick nitrogen-dominated atmosphere. Ammonia is believed to be important to maintaining nitrogen in Titan's atmosphere. Ammonia is seen in clouds in the atmospheres of Jupiter and Saturn, but has yet to be detected on any of the satellites. This may be because all forms of NH3 are unstable in the ambient conditions of the satellites surfaces or that its spectral features are altered by other components of the surface, and have not been identified. It has recently been demonstrated[1] that brightening occurs in Titan's atmosphere that is transient on the time-scale of months. The spectral shape of the brightening is more consistent with that of the transient apparition of a pure ammonia frost than of an ammonia monohydrate or ammonia dihydrate frost. However, the phase behavior of the ammonia water system has peritectics at compositions of 1:1 and 1:2. These hydrate forms would be expected to dominate if the frost, or the reservoir from which the frost was derived had any water present. Physical mechanisms for producing measurable quanitities of anhydrous ammonia can include chemical dehydration or dehydration of the vapor phase - but it is challenging to store significant quantities of the anhydrous material because of the phase behavior in the solid state. [1] Nelson, R.M., et al. Saturn's Titan: Surface Change, Ammonia, and Implications for Atmospheric and Tectonic Activity., Icarus, 199, pp. 429-441, 2009 This work was performed at JPL under contract to NASA
    No preview · Article · Dec 2009
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    ABSTRACT: In 2007 a JPL rapid mission architecture (RMA) analysis team identified and evaluated a broad set of mission architecture options for a suite of scientific exploration objectives targeting the Saturnian moon Enceladus. Primary science objectives were largely focused on examination of the driving mechanisms and extent of interactions by the plumes of Enceladus recently discovered by Cassini mission science teams. Investigation of the architectural trade space spanned a wide range of options, from high-energy flybys of Enceladus as a re-instrumented expansion on the Cassini mission, to more complex, multi-element combinations of Enceladus orbiters carrying multiple variants of in-situ deployable systems. Trajectory design emerged as a critical element of the mission concepts, enabling challenging missions on Atlas V and Delta IV-Heavy class launch vehicles. Various Enceladus Flagship-class mission concepts identified were analyzed and compared against several first-order figures of merit, including mass, cost, risk, mission timeline, and associated science value with respect to accomplishment of the full set of science objectives. Results are presented for these comparative analyses and the characterization of the explored trade space.
    No preview · Conference Paper · Apr 2009
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    ABSTRACT: Titan is known to have a young surface. Here we present evidence from the Cassini Visual and Infrared Mapping Spectrometer that it is currently geologically active. We report that changes in the near-infrared reflectance of a 73,000 km2 area on Titan (latitude 26° S, longitude 78° W) occurred between July 2004 and March of 2006. The reflectance of the area increased by a factor of two between July 2004 and March–April 2005; it then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again, establishing a new maximum. Thereafter, it trended downward for the next three months. Detailed spectrophotometric analyses suggest these changes happen at or very near the surface. The spectral differences between the region and its surroundings rule out changes in the distribution of the ices of reasonably expected materials such as H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of NH3 frost over a water ice substrate. NH3 has been proposed as a constituent of Titan's interior and has never been reported on the surface. The detection of NH3 frost on the surface might possibly be explained by episodic effusive events occur which bring juvenile ammonia from the interior to the surface. If so, its decomposition would feed nitrogen to the atmosphere now and in the future. The lateral extent of the region exceeds that of active areas on the Earth (Hawaii) or Io (Loki).
    No preview · Article · Feb 2009 · Icarus
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    ABSTRACT: The VIMS instrument on the Cassini spacecraft observes the surface of Titan through spectral 'windows' in its atmosphere where methane, the principal absorbing gas is transmitting. We previously have used VIMS to document changes in spectral reflectance and that have occurred on Titan's surface during Cassini's orbital tour at (latitude 26S, longitude 78W), (AGU spring meeting 2007). Having removed the possibility that the observed changes are either an atmospheric phenomenon or are the result of viewing angle (phase) effects, we conclude that physical changes in the chemistry or structure of the surface must be occurring. The size of the region suggests it may exceed the size of the largest active volcanic areas in the solar system. We now have explored additional sections of Titan's surface and have developed new techniques for locating surface changes over time. While some additional candidate areas for surface activity are suggested, confirmation is possible with the support of additional instruments on the Cassini Orbiter, particularly the radar instrument. The principal difficulty in implementing a coordinated program of observations with both instruments is due to the radar instrument's higher spatial resolution but small footprint on the surface relative to VIMS. In addition, the two instruments can not be used simultaneously on the same pass. Overlapping coverage will only be available after repeated flybys during Cassini's extended mission. This work done at JPL/CALTECH under contract with NASA
    No preview · Article · Dec 2007
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    ABSTRACT: On several occasions during its orbital tour the Cassini spacecraft has flown between the sun and Saturn in such fashion that the zero phase point passed through the rings. The Visual and Infrared Mapping Spectrometer (VIMS) recorded spectral image cubes (0.4< ? <5.2μm) that showed the opposition effect (OE) at zero phase. The OE is a spike in the reflected light observed near 0o phase when it is displayed as a function of phase angle. This is the first time the OE has been resolved for small areas on the rings. Previous work has shown that the OE arises from two distinct processes, shadow hiding (SHOE) and coherent backscattering (CBOE). The SHOE process causes an OE by the elimination of shadows cast by regolith grains upon one another as phase angle decreases. The CBOE process causes an OE by constructive interference between photons traveling in opposite directions along the same path within the medium. SHOE is expected to dominate the contribution to the OE in absorbing media where multiple scattering of photons is not significant. CBOE is expected to dominate the contribution to the OE in highly reflective media with much multiple scattering. We have made spectral scans the VIMS images that traverse the zero phase point. We selected narrow spectral bands that reflected a variety of wavelengths and reflectance levels. In this way, phase curves of the ringlet were obtained for each band. We have compared these data to data we acquired in the laboratory using the JPL long arm goniometer where we measured the phase curve of particulate materials that simulate the surface of Saturn's ring particles. We argue here that the OE is due to coherent backscattering because: 1) The theoretical CBOE function fit to the data is excellent. 2) The OE width is extremely narrow 3) The angular width of the peak increases with wavelength. CBOE theory also predicts that the width depends on the transport mean free path (TMFP) in the medium. We find that the OE is caused by coherent interactions between sub-particles in the outer layers of the ring particles, and that these sub-particles are of the order of 20-40 μm in size. A portion of this work was performed at JPL under contract with NASA
    No preview · Article · Aug 2007
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    ABSTRACT: We present the motivations and objectives of a new experimental cryo-ices initiative at JPL. This is a joint effort among experimentalists and theorists at JPL, in collaboration with specialists in ice properties.
    No preview · Article · Mar 2007
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    ABSTRACT: The bidirectional reflectance of a powder of spherical particles predicted by exact numerical solutions of the radiative transfer equation are more forward scattering than laboratory measurements, because the particles are more backscattering in a regolit
    No preview · Article · Mar 2007
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    ABSTRACT: A report on the implementation and testing of the Mars Borehole IR spectrometer. This spectrometer is designed to fit within a Mars drill, providing near real-time monitoring of the composition of the borehole wall.
    No preview · Article · Jan 2007
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    ABSTRACT: The near-infrared reflectance of a 73,000 km2 area on Titan changed between July 2004 and March of 2006. The reflectance of the region (latitude 26S, longitude 78W) increased twofold between July 2004 and March-April 2005. It then returned to the July 2004 level by November 2005. By late December 2005 the reflectance had surged upward again to a new maximum. It then declined for the next three months. Detailed analyses indicate that the brightenings are a surface phenomenon, making these the first changes seen on Titan’s surface. The spectral differences between the region and its surroundings rule out the ices of H2O, CO2, and CH4 as possible causes. Remarkably, the change is spectrally consistent with the deposition and removal of ammoniated materials. NH3 has been proposed as a constituent of Titan’s interior but not its surface or atmosphere. This transitory NH3 spectral signature is consistent with occasional effusion events in which juvenile ammonia is brought to the surface. Its decomposition may feed nitrogen to the atmosphere. The size of the region suggests it may exceed the size of the largest active volcanic areas in the solar system.
    Full-text · Conference Paper · Jan 2007
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    ABSTRACT: The Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini Saturn Orbiter returned spectral imaging data as the spacecraft undertook six close encounters with Titan beginning 7 July, 2004. Three of these flybys each produced overlapping coverage of two distinct regions of Titan's surface. Twenty-four points were selected on approximately opposite hemispheres to serve as photometric controls. Six points were selected in each of four reflectance classes. On one hemisphere each control point was observed at three distinct phase angles. From the derived phase coefficients, preliminary normal reflectances were derived for each reflectance class. The normal reflectance of Titan's surface units at 2.0178 μm ranged from 0.079 to 0.185 for the most absorbing to the most reflective units assuming no contribution from absorbing haze. When a modest haze contribution of τ=0.1 is considered these numbers increase to 0.089–0.215. We find that the lowest three reflectance classes have comparable normal reflectance on either hemisphere. However, for the highest brightness class the normal reflectance is higher on the hemisphere encompassing longitude 14–65° compared to the same high brightness class for the hemisphere encompassing 122–156° longitude. We conclude that an albedo dichotomy observed in continental sized units on Titan is due not only to one unit having more areal coverage of reflective material than the other but the material on the brighter unit is intrinsically more reflective than the most reflective material on the other unit. This suggests that surface renewal processes are more widespread on Titan's more reflective units than on its less reflective units.
    No preview · Article · Dec 2006 · Planetary and Space Science
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    ABSTRACT: Significant regional changes in the near-infrared reflectance of a 2800 km2 area on Titan occurred between July 2004 and March of 2006. The reflectance increased by a factor of two between July 2004 and March-April of 2005; it then decreased to the July 2004 level by November 2005. By late December 2005 the reflectance had surged again, slightly exceeding its earlier maximum. It then decreased in reflectance in the three following months through mid-March 2006. This behavior is inconsistent with tropospheric clouds of the type observed at Titan's South pole and high mid-latitudes. Application of a comprehensive radiative transfer model indicates that it is unlikely to be caused by a ground fog and most likely occurred at Titan's surface. This is the first direct evidence of short-term surface change on Titan. Inspection of the spectral differences between the spot and its surrounding terrain rules out changes in the distribution of the ices of H2O, CO2, and CH4 as the cause. However, the spectral change is consistent with what would be expected from NH3 frost. Interpretations include changing surface deposits due to abrupt tectonic or volcanic activity. This is the first evidence for currently active tectonic processes such as volcanism on Titan. This work done at JPL/CALTECH under contract with NASA
    No preview · Article · Dec 2006
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    Full-text · Conference Paper · Mar 2006
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    Full-text · Conference Paper · Mar 2006
  • W. D. Smythe · R. M. Nelson · J. H. Shirley · M. C. Boryta
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    ABSTRACT: Spectra and optical constants of ammonia frost are used to assess the detectability of ammonia frost viewed through Titan's atmospheric windows in the spectral range 1-5 µm.
    No preview · Article · Mar 2006
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    ABSTRACT: The National Research Council's solar system exploration decadal survey identified Jupiter's moon Europa as its highest-priority destination for near-term exploration. Voyager and Galileo missions to the Jupiter system provided evidence consistent with a subsurface ocean on Europa, which is of great interest as a potential abode for extraterrestrial life. This paper describes a conceptual flagship-class Europa orbiter concept that was assumed to launch as early as 2012, arriving at Europa approximately 8 years later using inner solar system gravity assists to reach Jupiter. Jupiter's intense radiation environment limits the mission duration at Europa to 30 days for this study, though the duration is a result of multiple trades and is by no means fixed. The Europa subgroup of the outer planets assessment group identified six primary science objectives for this concept. An ~150-kg instrument suite selected for the study addresses those objectives. Large heliocentric distances, high power levels required, and especially the harsh Jovian radiation environment drove the selection of radioisotope thermoelectric generators (RTGs) for all onboard electrical power, with the excess heat aiding spacecraft thermal control. Mass and architecture trades were performed using different spacecraft trajectories, launch vehicle types, radioisotope power systems, and mission durations. The study shows that new mission constraints allow a scientifically compelling Europa orbiter mission that might also deliver a Europa lander
    Full-text · Conference Paper · Jan 2006

Publication Stats

2k Citations
313.95 Total Impact Points

Institutions

  • 2011
    • University of Nantes
      Naoned, Pays de la Loire, France
  • 2006-2009
    • NASA
      • Earth Sciences Division
      Вашингтон, West Virginia, United States
  • 1991-2009
    • California Institute of Technology
      • Jet Propulsion Laboratory
      Pasadena, California, United States
  • 2000-2005
    • University of Pittsburgh
      • Department of Geology and Planetary Science
      Pittsburgh, PA, United States
  • 2001
    • University of California, Los Angeles
      • Institute of Geophysics and Planetary Physics
      Los Ángeles, California, United States