Planetary Sciences [P]

 CC:Hall E  Monday  1400h

Planetary Sciences General Contributions II Posters

Presiding:  A R Hendrix, Caltech/JPL


Jupiter Thermospheric General Circulation Model (JTGCM): Auroral Thermal Balances

* Majeed, T (, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States
* Majeed, T (, American University of Sharjah, University City, Sharjah, Sha 26666, United Arab Emirates
Waite, J H (, Southwest Research Institute, P. O. Box 28510, San Antonio, TX 78228, United States
Gladstone, G R (, Southwest Research Institute, P. O. Box 28510, San Antonio, TX 78228, United States
Bougher, S W (, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109, United States

We use our three-dimensional Jupiter Thermosphere General Circulation Model (JTGCM) to quantify thermal processes that take place in the auroral thermosphere. These processes tend to control the thermal budget in the Jovian ovals and polar caps, and to maintain thermospheric temperatures consistent with those derived from multispectral observations of Jupiter's aurora. The main heat source in the JTGCM that drives the thermospheric flow is high-latitude joule heating resulting from frictional motion of the ions relative to the neutrals. A secondary source of heating that dominates the exospheric region of the Jovian ovals is the auroral process of particle precipitation. Both sources of high-latitude heating in the JTGCM are strongly related to the current system in the outer magnetosphere that allows plasma to flow in and out of the Jovian ionosphere. The mapping of this flow to ionospheric altitudes gives rise to an ion drag process that dominates the neutral momentum forcing near the altitude of the ionospheric peak. We find that the ion drag and joule heating inputs in the JTGCM significantly intensify the underlying global thermospheric circulation, thereby affecting the distribution of the neutral temperature. Global simulations of the Jovian thermospheric dynamics indicate strong neutral outflows from the auroral ovals with velocities up to 1.9 km/s and subsequent convergence and downwelling at the Jovian equator. Such circulation is shown to be an important mechanism for transporting significant amounts of auroral energy to the rest of the planet and for regulating the global heat budget in a manner consistent with temperature observations of Jupiter's oval and polar cap regions. Adiabatic expansion of the neutral atmosphere resulting from outward flows is found to be an important source of cooling the auroral exosphere. The distribution of neutral temperature from 1 ýbar to 1 nbar is determined by the thermal balance between the total heating caused by joule and adiabatic heating processes and dynamical cooling mainly from the hydrodynamic advection process. The thermal balance of the Jovian thermosphere below the homopause (≥ 1 μbar) is shown to be dominated primarily by wind transport processes. The heating in this region both for the Jovian ovals and polar caps, is due to hydrodynamic advection and adiabatic compression processes. This dynamical heating is efficiently dissipated by hydrocarbon cooling through CH4 and C2H2 infrared radiation at 7.8 μm and 12.6 μm, respectively.


The Europa Jupiter System Mission

* hendrix, A R (, Caltech/JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
Clark, K (, Caltech/JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
Erd, C (, ESTEC, ESA, Noordwijk, Netherlands
Pappalardo, R (, Caltech/JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
Greeley, R R (, Arizona State Univ., Tempe, Tempe, AZ 85287, United States
Blanc, M (, Ecole Polytechnique, Paris, Paris, 2200, France
Lebreton, J (, ESTEC, ESA, Noordwijk, Netherlands
Van Houten, T (, Caltech/JPL, 4800 Oak Grove Dr., Pasadena, CA 91109, United States

Europa Jupiter System Mission (EJSM) will be an international mission that will achieve Decadal Survey and Cosmic Vision goals. NASA and ESA have concluded a joint study of a mission to Europa, Ganymede and the Jupiter system with orbiters developed by NASA and ESA; contributions by JAXA are also possible. The baseline EJSM architecture consists of two primary elements operating in the Jovian system: the NASA-led Jupiter Europa Orbiter (JEO), and the ESA-led Jupiter Ganymede Orbiter (JGO). The JEO mission has been selected by NASA as the next Flagship mission to the out solar system. JEO and JGO would execute an intricately choreographed exploration of the Jupiter System before settling into orbit around Europa and Ganymede, respectively. JEO and JGO would carry eleven and ten complementary instruments, respectively, to monitor dynamic phenomena (such as Io's volcanoes and Jupiter's atmosphere), map the Jovian magnetosphere and its interactions with the Galilean satellites, and characterize water oceans beneath the ice shells of Europa and Ganymede. EJSM will fully addresses high priority science objectives identified by the National Research Council's (NRC's) Decadal Survey and ESA's Cosmic Vision for exploration of the outer solar system. The Decadal Survey recommended a Europa Orbiter as the highest priority outer planet flagship mission and also identified Ganymede as a highly desirable mission target. EJSM would uniquely address several of the central themes of ESA's Cosmic Vision Programme, through its in-depth exploration of the Jupiter system and its evolution from origin to habitability. EJSM will investigate the potential habitability of the active ocean-bearing moons Europa and Ganymede, detailing the geophysical, compositional, geological and external processes that affect these icy worlds. EJSM would also explore Io and Callisto, Jupiter's atmosphere, and the Jovian magnetosphere. By understanding the Jupiter system and unraveling its history, the formation and evolution of gas giant planets and their satellites will be better known. Most important, EJSM will shed new light on the potential for the emergence of life in the celestial neighborhood and beyond. The EJSM mission architecture provides opportunities for coordinated synergistic observations by JEO and JGO of the Jupiter and Ganymede magnetospheres, the volcanoes and torus of Io, the atmosphere of Jupiter, and comparative planetology of icy satellites. Each spacecraft could and would conduct "stand-alone" measurements, including the detailed investigation of Europa and Ganymede, providing significant programmatic flexibility. Although engineering advances are needed for JEO (radiation designs) and JGO, no new technologies will be required to execute either EJSM mission element. The development schedule for the mission is such that a technology developed by 2012 - 2013 could easily be incorporated if it enhances the mission capability. Risk mitigation activities are under way to ensure that the radiation designs are implemented in the lowest-risk approach. The baseline mission concepts include robust mass and power margins.


Cassini Data in the PDS: Strategies for Usability

* Alexander, C J (, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States
Beebe, R (, New Mexico State University, P. O. Box 30001, MSC 4500, Las Cruces, NM 88003-8001, United States
Pappalardo, R T (, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States

Four years after the start of the historic Cassini mission, a wealth of data has accumulated in the Planetary Data System (PDS). Data from the orbiter consists (only a partial list is included here) of images from ISS (the camera system), and the Radar system; spectra from remote sensing instruments: UVIS (the ultraviolet spectrometer), and VIMS (the visible/infrared spectrometer); radiometry from CIRS; electron and ion sensor data from CAPS (the plasma instrument); high energy electron, ion, and neutral sensor data as well as images from MIMI (the energetic particle instrument); magnetic field data from MAG (the magnetometer); ion and neutral count data from INMS (the mass spectrometer); dust count data from CDA (the dust detector); and raw data from the radio science experiment. Data from the Orbiter is spread across several nodes of the PDS including the Imaging Node, the Rings Node, the Atmospheres Node, and the Planetary Plasma Interactions Node. Other relevant PDS nodes for the purposes of making best use of the data include the Engineering Node, and the Navigation and Ancillary Information Node. Tools for reading, plotting, finding ephemeris of, and other tools are also available. Prospective users must make themselves aware of gaps, calibration issues, instructions that are part of the documentation, and other nuances of using these data. The Cassini Project is interested in the accessibility of these data to the larger community. The Cassini Project recently conducted a 'Usability' study with beta testers to assess the ease of use of these data for investigators not familiar with Cassini. Many of the data sets, which included detailed instructions for users to perform their own calibrations, were found to be non-trivial for first-time users. Some of the data sets require knowledge of specialized software - including SPICE software - documentation of which is provided but which may be non- trivial to use. In this talk we will present the basic components of each of the data sets, how to get started, lessons learned from the experiences of first-time users, and we welcome feedback from the community. The PDS Home Page is given at the URL below. The Cassini Project is compliant with all NASA archiving requirements. The work at the Jet Propulsion Laboratory, California Institute of Technology, was supported by NASA. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.


Phoebe and Friends

* Gaskell, R W (, Planetary Science Institute, 1700 E Fort Lowell, Tucson, AZ 85719, United States
Mastrodemos, N (, JPL/CALTECH, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
Rizk, B (, University of Arizona Lunar & Planetary Laboratory, 1629 E. University Blvd., Tucson, AZ 85721, United States

We present a high-resolution global topography model (GTM) of Saturn's satellite Phoebe, derived from Cassini images taken during the flyby on June 11, 2004. The model is composed of about 1.57 million vectors and was synthesized from 523 maplets. Each maplet is a 99x99 pixel topography and albedo map constructed from the ensemble of images using stereophotoclinometry. The central point of each maplet is a control point. The 523 control points were determined from 22708 observations, about 43 per control point, and the RMS measurement residuals were about 180 meters per degree of freedom. The model has a volume of about 5 million cubic kilometers and a surface area of about 150000 square kilometers, so the model's resolution is about 300 m. The pole was determined from the set of control points to be at RA 356.86 +/- .02 degrees and DEC 77.878 +/- .004 degrees. This study is part of ongoing work on Saturn's satellites. We shall also present preliminary models for several other satellites, including Mimas, Enceladus, Iapetus and Tethys.


Multispectral Study of the Schrödinger Impact Basin

* Shankar, B (, Department of Earth Sciences, University of Western Ontario, 1151 Richmond St., London, ON N6A 5B7, Canada
Osinski, G (, Department of Earth Sciences, University of Western Ontario, 1151 Richmond St., London, ON N6A 5B7, Canada
Antonenko, I (, Department of Earth Sciences, University of Western Ontario, 1151 Richmond St., London, ON N6A 5B7, Canada
Stooke, P J (, Department of Geography, University of Western Ontario, 1151 Richmond St., London, ON N6A 5C2, Canada

The Schrödinger impact basin is located on the lunar far side near the south pole (76oS, 134oE) and is one of only two young multiring impact basins on the lunar surface [1]. With a diameter size of 312 km and basin floor 2-3 km deep, Schrödinger is the least modified impact basin of its size. A peak ring structure 150 km in diameter lies on the basin floor, formed by uplift of pre-Schrödinger crustal materials. Ejecta material, smooth in texture, covers the basin walls and extends out onto the surrounding surface up to 100 km in all directions. The first geological map published of Schrödinger was generated using preliminary Clementine data [1]. The map described the geology and geomorphology within the inner basin with smooth and rough plains of shocked material occupying most of the basin floor. The rough plains are identified by presence of hummocks, swales, and low knobs. Smooth plains have no discernable features identifiable. Ghost craters are found along both smooth and rough patches. A volcanic vent in the inner eastern corner of Schrödinger is interpreted as a source for pyroclastic eruptions within the area. Located along the volcanic vent is a north-east trending graben. There are thin patches of impact melt sheets along the basin walls and peak ring. A lobate ridge located near the centre of the inner basin is interpreted as having formed by buckling of the melt sheet. A more recent geologic map using high resolution Clementine UVVIS data and topography data is in agreement with the proposed geology within the Schrödinger basin [2]. Contacts between various units are better outlined in the recent map. Using spectra derived from high resolution Clementine UVVIS images and Lunar Prospector data we determine the composition of impact melt, impact ejecta, and the extent of proposed cryptomare deposits [3]. We also use Fe, Th, and Ti abundance in determining the composition of these units. Our goal is to determine the abundance and distribution of impact melt relative to volcanic products and ejecta units. We are also addressing possible differentiation of the melt sheet as a crater the size of Schrödinger has sufficient time to cool and allow for melt to differentiate. References: [1] Shoemaker, E.M., Robinson, M.S., and Eliason, E.M. (1994) Science. 266. 1851- 1854. [2] Mest, S. C.; Van Arsdall, L. E. (2008) NLSI Lunar Science Conference. Abstract 2089. [3] Antonenko, I. (1999) PhD Thesis, Brown University. Chapter 4, pp 13-14.


Microscopic Effects of Shock Metamorphism in Crystalline Rocks Correlated With Shock Induced Changes in Density, Haughton Impact Structure

* Singleton, A C (, Dept. of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7, Canada
Osinski, G (, Dept. of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7, Canada
Moser, D (, Dept. of Earth Sciences, University of Western Ontario, 1151 Richmond Street, London, ON N6A 3K7, Canada

Asteroid and comet impacts are an important geological process on all solid planetary bodies, including Earth, and involve pressures and temperatures that may reach several hundred GPa and several thousand K [1] over very limited spatial and temporal scales. This results in shock metamorphism and alters the target material on both megascopic and microscopic scales [2]. Many shock metamorphic features are unique to hypervelocity impact environments and are, therefore, diagnostic of such an event [1,2]. Of particular interest for this study is the effect of hypervelocity impact on the density of the target material. In the case of crystalline target rocks, shock metamorphism results in an increase of pore space and impact induced fractures which act to decrease the density. The Haughton impact structure is a well-preserved late Eocene (39 ± 2 Ma) complex impact structure, situated near the western end of Devon Island (75°22'N, 89°41'W) [3]. The geology of the area consists of a sedimentary sequence unconformably overlying crystalline Precambrian gneisses of the Canadian Shield. Since the impact, Devon Island has remained tectonically stable and Haughton remains well-preserved despite being subjected to several glaciations. The excellent preservation of the structure is largely due to the primarily cold and relatively dry environment that has existed in the Arctic since the Eocene [3]. Samples of crystalline material were collected from 36 sites within the impact breccia unit of the Haughton impact structure. These samples display a wide range of density and physical appearance. The type of shock effect(s) created depends upon the pressures and temperatures involved as well as the composition, density and material's location in the target. The samples found in the Haughton impact structure show a wide range of shock effects and thus were exposed to a variety of different conditions likely due to their in-situ positions relative to the impact. Polished thin sections from a representative selection of shocked and unshocked Precambrian gneiss from the Haughton impact structure were investigated in transmitted light with a petrographic microscope and each sample was assigned a shock level based on the identification of shock features. Features identified include kink banding in mica, planar deformation features in quarts and feldspar, and partial or complete melting of various minerals. The density of each sample was also measured. Preliminary results suggest a correlation between decreasing density and increasing shock level. These results may be important not only for understanding shock metamorphism, but also for astrobiology. Impact- induced density decreases in crystalline rocks present opportunities for microbial colonization that would not exist otherwise [4]. The colonization of the shocked material in craters represents a potential mechanism for pioneer organisms to invade an impact structure in the earliest stages of post-impact primary succession. This is a possible mechanism by which microbes may gain a foothold on planetary surfaces that do not have other hospitable habitats. This may be of particular relevance to Mars [4]. [1] Langenhorst, F., Bulletin of the Czech Geo. Survey, 2002. 77, (4): p. 265-282. [2] Therriault, A.M. et al. Bul- letin of the Czech Geo. Survey, 2002. 77, (4): p. 253-263. [3] Stöffler, D. (1971) Journal of Geo-physical Research, 79, (23) [4] Cockell, C.S. et al. Met. & Pl. Sci., 2002. 37, p. 1287-1298.