P41A-0185
Calibration of Herschel/HIFI in the CO Absorption Lines of Mars
The European Space Agency's cornerstone project HERSCHEL is a space based 3.5m-telescope for exploration of the Universe in the spectral range from far-infrared to sub-millimetre wavelength (57-670 μm). The science payload consists of three instruments: 1. PACS, a bolometer detector array camera and a low- to medium-resolution spectrometer to perform imaging photometry and imaging line spectroscopy in the 60--210μm wavelength band, 2. SPIRE, an imaging photometer covering the 250--500 μm range, and an imaging Fourier Transform Spectrometer covering 200--670 μm, and 3. HIFI, a high resolution heterodyne receiver covering the frequency range 480--1910 GHz with a resolving power of up to 107. In order to achieve an absolute flux calibration accuracy of better than 5 percent for HIFI, it is intended to use Uranus and Mars as primary flux standards for continuum radiation. But especially Mars seems to be a challenging calibration source, because numerous rotational absorption lines -- caused by CO and H2O in Mars tenuous atmosphere -- disturb the continuum radiation emitted by the surface. So usually these wavelength regions are omitted for an accurate instrument calibration. However, we have studied the emitted radiation especially in the deep core of the CO absorption lines, because the spectral lines are optically thick at these frequencies and Mars can be treated as a pure gas planet without any need to model the surface emission. Using a detailed radiation transfer model and a general circulation model to predict the seasonal variation of Mars' atmosphere we found for several CO lines a variability of Mars' brightness temperature of less than ±5 percent. So we suggest not to avoid the rotational CO absorption lines of Mars, but to observe especially the line center of all observable CO lines in order to increase the accuracy of the absolute flux calibration of HIFI.
P41A-0186
Martian Gravity Field Mean Model and its Time Variations From Mars Global Surveyor and Odyssey Data
The MGS and Odyssey missions have provided a wealth of orbit tracking data which are used for modeling the Martian gravity field and its time variations which are due to seasonal mass transfers between the planet surface and its atmosphere. We collected most observations covering the entire MGS orbital phase (1998-2006) and the Odyssey mapping mission between 2002 and mid 2007. Doppler and range measurements over those 4.5 Martian years have been processed in arcs of a few days duration each, using improved standards and background models. A static spherical harmonic model complete to degree and order 95 has been computed, together with the k2 Love number and time variations of the second and third degrees lumped zonal coefficients at ten day interval. The solution is compared to previously derived models by means of statistical and orbital quality tests and correlations with topography. The new solution is more robust than the ones derived in 2005 and 2006 by the authors, mostly due to the addition of Odyssey data and also the longer data span. The value of k2 is stable with respect to various parameterization and regularization strategies and supports the hypothesis of a fluid core of Mars.
P41A-0187
Flank Terraces of Martian Shield Volcanoes: Architecture and Formation
Flank terraces are topographically subtle bulge-like structures on the sides of numerous Martian shield volcanoes. They have a gentle convex profile in cross section. These structures have an arcuate outline in plan, and are arranged in a distinctive, imbricate "fish scale" pattern about each terraced edifice. Terraces are generally regarded as compressive features, formed by magma chamber inflation or lithospheric flexure. Some workers argue they are extensional in nature however, due to flank relaxation or gravitational slumping. Previously recognised on Olympus Mons and the Tharsis Montes (Ascraeus, Pavonis, and Arsia), we show that this pattern also exists on Elysium Mons, Hecates Tholus, Albor Tholus, and Ceraunius Tholus, and Alba Patera. Terrace distribution differs between volcanoes, but the characteristic pattern remains the same. Terraces must be late-stage/reactivated structures relative to volcano growth, as they remain visible today. The mechanism responsible for terrace formation probably acts throughout the edifices, as terraces occur at all volcano elevations. Differences in distribution may be due to variations in edifice internal structure, geometry, or the interplay between local and regional stresses. That terraces occur across such a range of Martian volcanoes implies they are size-, slope-, and volcano age-independent structures. The presence and number of other tectonic structures, e.g. calderas and gräben, also vary between terraced volcanoes. Like these other structures, flank terraces may be a fundamental feature of Martian volcano development. In light of these observations, existing formation mechanism hypotheses must be revisited. Magma chamber tumescence, which may have occurred to varying extents on these volcanoes, does not produce convex terrace structures. Both flank relaxation and shallow slumps are associated with volcano spreading, yet none of the Martian examples shows evidence of radially oriented gräben or collapse scars. A feature common to all terraced volcanoes, however, is their large mass. Flexure of the underlying viscoelastic lithosphere in response to these loads may thus lead to internal edifice compression sufficient to form radially directed, circumferentially oriented thrusts.
P41A-0188
Using Combined THEMIS Visible and Infrared Images to map Martian Topography and Slope- corrected Surface Thermal Properties
Kirk et al. (2005) empirically deconvolved visible and thermal-infrared THEMIS data, isolating topographic information that produced an accurate digital-terrain model (DTM). Described here is the next step wherein we use the same dataset (Columbia Hills area, Mars) in conjunction with the KRC thermal model (Kieffer et al., 1977) to quantitatively derive and map slope-corrected thermophysical properties. Observed surface temperatures, at high spatial resolution, are a function of many variables such as: slope, albedo, thermal inertia, time, season and atmospheric opacity. We constrain each of these variables to construct a DTM and maps of slope-corrected albedo, slope/albedo-corrected thermal inertia, and surface temperatures across an entire scene for any time of day or year and any atmospheric opacity. DTMs greatly facilitate analyses of the Martian surface, but generating these data is a challenge. The MOLA global dataset does not have sufficient resolution (~3 km) to be combined with newer datasets (e.g. HiRISE, CTX, THEMIS, MOC, and CRISM), so new techniques to derive high-resolution DTMs are always being explored. Stereo imaging produces quality, high-resolution DTMs but is limited in the amount of available coverage. Photoclinometry techniques on visible-wavelength images have been widely investigated with varying degrees of success, but accounting for albedo variations across a scene has been an historical weakness of this method. Here we discuss a technique of combining THEMIS visible and thermal infrared (both daytime and nighttime) observations (Christensen et al., 2004) in such a manner that albedo variations in the scene are cancelled, allowing the production of a high-resolution DTM via photoclinometry techniques that are largely free of albedo-induced errors. We employ the KRC thermal-diffusion model to generate models of slope-corrected thermal properties from the resultant DTM and THEMIS observations. This technique can provide new perspectives and insights into studies of surface thermodynamics, and provide engineering constraints to future missions. References: Christensen, P.R. et al., Space Science Reviews, 110, 85-130, 2004; Kieffer, H.H. et al., Journal of Geophysical Research, 82(28), 4249- 4291, 1977; Kirk, R.L. et al., Photogrammetric Engineering & Remote Sensing, v 71, n 10, p 1167-1178, October 2005.
P41A-0189
Geology of the NW Rim of the Hellas Basin
Hellas is a significant region for evaluating volatile abundance, distribution, and cycling as well as changes in surface conditions on Mars, given the nature, diversity, and range in ages of potential water- and ice-related landforms. The highland terrains north of the basin have been of recent interest due to the discovery of phyllosilicates around and within impact craters. Current work focuses on the evolution of Hellas' NW rim, where an abrupt transition from basin floor deposits to circum-Hellas crater terrain is observed. Preliminary observations suggest that the NW Hellas rim can be divided into four zones that have different surface characteristics and lie in different elevation ranges: 1) Terra Sabaea highlands (above 500m), 2) Terra Sabaea plains (-2000m - 500m), 3) Hellas basin rim (-5800m - -2000m), and 4) Hellas Planitia/basin floor deposits (below -5800m). All of these zones show significant numbers of moderate to large impact craters, suggesting that the basic geologic framework of the region was established early in Martian history. However, there are clear differences in the types of landforms and materials exposed as well as differences in densities of large impact craters and crater degradation states. A significant and complex sedimentary history can be inferred given that many craters contain interior layered deposits, as well as by a multitude of scarps and valleys within intercrater plains. Crater interior deposits, typically exposed by irregular scarps, exhibit layering and clear differences in erosional morphology and thermophysical properties. We are characterizing the observed deposits and layered sequences, as well evaluating geologic and stratigraphic patterns in order to distinguish potential large-scale Hellas-centric systems from localized, spatially and/or temporally scattered depositional sinks. The zone of Terra Sabaea plains exhibits remnants of cratered highlands, including large infilled craters, within younger plains that appear to be part of a larger depositional shelf along Hellas' north rim. This zone is also at elevations similar to smooth and channeled plains along Hellas' east rim, which may be related to flooding from Reull Vallis and/or accumulation of atmospheric volatiles due to circulation patterns off of the south pole. Comparisons of the geologic evolution of highland terrains around the Hellas perimeter should yield important constraints on past climate regimes.
P41A-0190
Investigation of the Effects of H2O on Melting of a Primitive Martian Mantle Composition
Extensive signs of past water exist on the Martian surface. While many experiments have been performed on hydrated terrestrial compositions, it is only recently that such experiments have been applied to Mars. High- pressure experiments were performed in a piston cylinder apparatus using a synthetic composition of Martian meteorite Yamato 980459, with 0.5 weight percent H2O added. This composition was chosen because it is a very primitive meteorite, and experiments suggest that it may represent a primary melt of the Martian mantle. The addition of 0.5 weight percent H2O lowered the liquidus temperature and decreased the slope of the liquidus slightly. Four phase assemblages were observed: 1) liquid, 2) olivine + liquid, 3) olivine + orthopyroxene + liquid, and 4) orthopyroxene + pigeonite + liquid. The multiple saturation point could exist at a higher pressure than the anhydrous experiments, indicating a hydrated Yamato 980459-type melt could form deeper within the Martian mantle.
P41A-0191
Phase Transition Evolution and Convection Style in the Martian Mantle
The higher iron content of the Martian mantle as compared to Earth's mantle results in a mineralogy and phase transition pattern which is somewhat different to that of the Earth; for instance, ringwoodite appears already at lower pressures than wadsleyite. Moreover, the two-phase loops in the Mg2SiO4--Fe2SiO4 system are broader and their position and width seem to be more sensitive to changes in temperature. Another concern is the uncertainty about the depth of the core--mantle boundary in Mars, which happens to lie at about the depth of the ringwoodite-(perovskite+magnesiowüstite) transition. Previous studies have already demonstrated the possibility that Mars had a perovskite layer at the base of its mantle which may have disappeared during the history of the planet as a consequence of secular cooling. In our study, we attempt to model the evolution of the phase transition patterns, i.e. the changes in position and width of transitions and the mineralogical changes, as a consequence of secular cooling and discuss their effect on the long-term convection style of the martian mantle.
P41A-0192
Influence of Fe content on the creep properties of olivine under anhydrous and hydrous conditions
High-temperature, high-pressure compressive creep experiments were performed on both wet and dry aggregates of Fa75 in a gas-medium deformation apparatus. The results from these experiments are compared with those for San Carlos olivine, Fa10, and our previous results on Fa30 and Fa50 in order to provide a basis for comparing convection models for the mantle of Earth with those for the more iron-rich mantle of Mars. Samples were fabricated from powders of Fa75 that were synthesized from mixtures of Fe2O3 and SiO2 combined with San Carlos olivine. The Fa75 powders were cold-pressed into Fe capsules and then hot-pressed at 300 MPa, 1473 K for 3 h. The average grain size of the resultant hot-pressed samples was ~40 μm. For experiments under hydrous conditions, three drops of deionized water were added before sealing the sample within telescoping Fe cans for deformation. Water bubbles were present both within olivine grains and along grain boundaries, demonstrating that the samples were water-saturated. Triaxial compressive creep experiments were carried out in a servo-controlled, internally heated gas-medium apparatus at 50 K intervals between 1273 and 1423 K and a confining pressure of 300 MPa with differential stress of 10 to 300 MPa. For each sample, creep tests were performed at several differential stresses at a constant temperature to determine the stress exponent or at several temperatures to determine the activation energy for creep. Under anhydrous conditions the viscosity of samples of Fa75 is more than a factor of 10 lower than the viscosity of Fa50. Previous experiments showed a similar relationship between Fa50 and Fa30 and Fa30 and Fa10. Under hydrous conditions the viscosity of samples of Fa75 are about a factor of 5 lower than the viscosity of Fa50, which is less than that observed between Fa50 and Fa30 or Fa30 and Fa10. The viscosity of a sample of a specific Fe:Mg ratio deformed under hydrous conditions is a factor of 10 lower than its counterpart deformed under anhydrous conditions. Therefore, at the same thermodynamic conditions (e.g. P, T, water fugacity), the viscosity of the more Fe-rich mantle of Mars will be a factor of about 3 lower than the mantle of Earth.
P41A-0193
Tidally Induced Core Dynamo of Mars
We study tidal excitation of elliptical instability inside the liquid core of Mars by an asteroid similar to one that created Hellas basin. The growth time of the excitation is 5,000 -20,000 years when the asteroid is at a distance of 35,000 – 50,000 km. We investigate the spin-orbit coupling of the asteroid and Mars through their tidal interaction. An captured prograde asteroid can excite the elliptical instability of the Martian core for only a few million years before colliding with Mars, whereas a captured retrograde asteroid can excite the elliptical instability for hundreds of millions of years before colliding on Mars. The tidal energy dissipation rate is over two orders of magnitude greater than the magnetic energy dissipation rate. Our results indicate that a retrograde Hellas-type asteroid is quite capable of exciting the elliptical instability in the Martian core, thus providing a candidate process to drive a core dynamo
P41A-0194
Modeling the Currents in the Martian Magnetotail due to Ionospheric Electron Transport from Dayside to Nightside
In previous work, we observed seasonal, night time enhancements in the Mars Global Surveyor (MGS) electron omnidirectional flux data at low energy levels over the geographical region at the west edge of the crustal fields (at around 70° S and between 30° E and 150° E). We proposed that photoelectrons generated over the crustal sources on the Martian dayside are transported along lines of reconnected Interplanetary Magnetic Field (IMF) to the nightside populating current sheets in the Martian tail. Results of modeling the distribution of current sources in the nightside using magnetic field data during these events and analysis of the estimated draping direction using the dayside magnetic field data supported our proposal. However, observation of the time evolution of this phenomenon is not convenient due to lack of synoptic MGS data. Recently, we have employed simple, empiric flow model based on ideal magnetohydrodynamics (MHD) where the magnetic field is frozen into the plasma, and predict field features and the origin of the observed phenomena. In this paper, we present results of this approach and modeling strategy.
P41A-0195
Simultaneous Photoelectron and Ion Measurements in the Martian Tail
The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment on the Mars Express spacecraft contains an Electron Spectrometer (ELS), and an Ion Mass Analyzer (IMA). While orbiting Mars, the ELS is able to observe peaks in the photoelectron spectrum due to photoionization of carbon dioxide and atomic oxygen by a solar He 30.4 nm photon. The source of these peaks is the dayside Martian ionosphere, with the majority of photoelectrons created at the exobase where the density is greatest. A fraction of these photoelectrons is transported to spacecraft altitudes. Since atmospheric photoelectrons originating from the dayside ionosphere are observed in the tail of Mars, by charge conservation there should also be low energy planetary ions at these locations. Recent improvements in the sensitivity of IMA have made it possible to study cases in which ions are detected simultaneously with the ionospheric photoelectrons. In this paper we survey the cases in which photoelectrons are observed in the Martian tail region, describe the characteristics of the simultaneously observed ions, and discuss the observations in terms of ion escape from the planet.
P41A-0196
Simulations of the Ionospheric loss rate of Mars
In the past four or five years a concerted effort to predict and understand the rate at which Mars is losing it ionosphere, thus it's atmosphere, has been underway. These efforts are simulations efforts and entail both MHD and kinetic simulations. This paper will present our most recent efforts to improve the predictions and test the models being used in the predictions. The tests to be presented cover topics such as numerical resolution issues, ionospheric model issues, the differences found when using ionospheric profiles or creating the ionosphere via solution of chemistry equations. The affect of these various tests on the predicted loss rates will be presented as well as topographic changes in variables such as the global electric field structures.
P41A-0197
The Magnetic Field Induced by the Solar Wind on the Dayside of Mars
The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on Mars Express can be used to measure the local magnetic field. The technique relies on the detection of the electron echoes. These are series of echoes that are equally spaced in time at the electron cyclotron period. The echoes are believed to be caused by the periodic return to the antenna of electrons that are accelerated during the sounder pulse by strong electric fields near the antenna. From the period of the echo, the magnetic field strength in the vicinity of the spacecraft can be computed. These scalar measurements are highly complementary to those obtained by the Mars Global Surveyor Magnetic Field Experiment (MAG/ER). The Cain et al. (2003) model is used for nightside magnetic field measurements where MARSIS data is from the dayside. The difference between the nightside and the dayside measurements is due to the electrical currents that flow in the dayside ionopause. An average magnetic field vector which is induced by the solar wind is calculated using a best-fit method for each periapsis pass. This result will contribute to the study of the Mars-solar wind interaction.
P41A-0198
Electron Densities in the Upper Ionosphere of Mars from the Excitation of Local Electron Plasma Oscillations
In addition to the remote sounding of the ionosphere, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on the Mars Express spacecraft, also excites local electron plasma oscillations. This paper summarizes the investigation of the local electron density using measurements of the locally excited electron plasma oscillation frequency. One of the advantages of this method is that the electron densities can be measured at very high altitudes, where remote ionospheric echoes cannot be detected. Measurements from 503 orbits over the period from August 4, 2005 to July 31, 2007 show that the average electron densities at a given solar zenith angle (SZA) decrease exponentially with increasing altitude. There is considerable variability at a given altitude due to the fact that the data at a specific altitude are obtained from different orbits. On the dayside of Mars, this exponential behavior continues up to altitudes of around 750 km. The scale height, in this altitude region, ranges between 130 km and 190 km. The average electron density is almost constant throughout the dayside in a given altitude range, but decreases rapidly as the spacecraft goes into the nightside. Simulations performed using different methods, show that the nearly constant density at a given altitude is due to transport effects. Investigation of individual orbits shows that the electron density throughout a pass often has large fluctuations, sometimes as much as ∆ne/ne ~ 50 %, on time scales as small as 8 s.
P41A-0199
Modeled Ion Densities of Comet 1P/Halley: a Comparison With Giotto's Ion Mass Spectrometer
The cometary plasma environment is largely influenced by a complex, closely linked series of chemical reactions. To better our understanding of this environment, we compare the results from our ion-chemical network calculation, consisting of a magnetohydrodynamics (MHD) as well as a chemistry model, with data from the Ion Mass Spectrometer collected during Giotto's fly-by at Comet 1P/Halley in 1986. The chemistry code, originally developed by Häberli et al. (1995, Astron. Ap. 297, 881), integrates the 24 most dominant species along streamlines which have been extracted from an MHD model of Comet 1P/Halley [Gombosi et al. (1996, JGR 101, 15233)]. The chemistry code includes a few hundred reactions for these species including photodissociation, photoionization, electron impact ionization, ion-molecule reactions, charge exchange, and dissociative ion- electron recombination. In this work we compare the measured and modeled densities of the C+, CH+, CH2+, CH3+, N+, NH+, NH2+, NH3+, NH4+, O+, OH+, H2O+, H3O+, CO+, HCO+, H3CO+, and CH3OH2+ ions along the Giotto trajectory from 200~000~km to roughly 1000~km at closest approach. Our results are in good agreement, although, in order to reproduce the data in the vicinity of the comet, an additional source for C+, CH+, as well as the CH2+ ions is needed. First investigations indicate that all three species are emerging from the same source which needs to have a short scale length of less than 500~km in order to accommodate with the measurements. Finally, we also show our results of the contact surface which is well resolved and in good agreement with the Giotto data.
P41A-0200
Sodium Exosphere of Planet Mercury: Particle Tracing
We will present the results of particle tracing simulations of heavy ions in magnetosphere of Mercury. In our study we use electric and magnetic fields from self-consistent hybrid simulations of Hermean environment. We consider three major release processes, namely photon stimulated description, solar wind sputtering, and micro-meteoroid vaporization to study distribution of energy and other characteristics in space and time. The released neutral atoms are ionized through photoionization processes after the sputtering. Part of our work will be focused on the possible measurements during three initial flybys of the MESSENGER spacecraft scheduled for 2008 and 2009.
P41A-0201
Characterizing Lunar Crustal Geology
In our initiative to return to the Moon, knowledge of regional crustal geology is necessary both for locating resources of scientific interest and for establishing a sustained human presence. Characterizing crustal geology with global remote sensing data is difficult due to the types of weathering processes experienced by an airless, geologically torpid planetary body, which tend to reduce lithologic contrast and obscure the lithology of true bedrock. Fortunately, these processes are relatively straightforward, involving parameters with largely understood, fixed rates of flux. We describe a methodology for characterizing the chemical and mineralogical compositions of discrete geologic units, interpreted from remotely sensed surface spectra. The method utilizes two established techniques: small impact ejecta viewing and extrapolation (SIEVE) (McCord et al., JGR 1981; Staid & Pieters, LPSC 29; Kramer et al., LPSC 36; Kramer et al., JGR (in review)) and spectral mixing analysis (SMA) (Adams & Gillespie, Cambridge Univ. Press 2006, and references therein). The results of this work will be invaluable for identifying regions of interest for current and future lunar missions, such as Chandrayaan-1, carrying NASA's Moon Mineralogy Mapper, and Lunar Reconnaissance Orbiter. Furthermore, the methodology can be used to explore other planetary bodies that experience similar weathering processes (e.g., Mercury, Ceres, Vesta, and Mars).
P41A-0202
Clasts of Bladed Serpentine in a K/T Boundary Layer From the Central North Pacific: Implications for Catastrophic Impact by a Chondritic Projectile
A 24-m long piston core (LL44-GPC3) retrieved marine sediments from the central North Pacific. At a depth of 2055-2056 cm downcore, a thin layer having an Ir anomaly of 10 ng/g was identified as the 65 m.y. old K/T boundary layer by Kyte et al.,1995. We studied 6 samples of clay selected from 2042-2060 cm by Jim Broda (Woods Hole Oceanographic Institution), and found that only the 1 cm-thick Ir layer contains many microtektites (impact glass), 4 crystals of silicon carbide (SiC), about 20 clasts of serpentine, usually associated with several grains of magnetite. We believe that this sharply defined Ir layer might have been deposited by a catastrophic event of relatively short duration, perhaps triggered by an impactor. Serpentine crystals in the clasts are blade-like, but may also be foliated or granular. Bladed crystals are reminiscent of barred textures, or excentroradial groups of olivine and/or pyroxene, commonly found in chondrules. We also found a fine-grained, white substance which forms veins between serpentine crystals, resembling "Saponite" reported in an interplanetary dust particle (IDP) which was also composed of serpentine, by Keller et al., 1992, who believed that the IDP had links to hydrated CI chondrites. Thus, the precursor of serpentine clasts found in the GPC3 core, might have been a CI, or a carbonaceous chondrite (carrier of SiC) whose collision with Earth might have set off a fireball capable of transporting serpentinized chondritic particles and grains of SiC to our core site in the North Pacific.
P41A-0203
Archaeology and Planetary Science: Entering a New Era of Interdisciplinary Research
Recent studies highlight the widening intersection between planetary and archaeological investigations, which will provide new avenues of funding and research for planetary scientists in the coming decades. Emergent research areas fall into five primary categories: 1) Enhancing anthropological investigations by utilizing planetary remote sensing techniques; 2) Mining archaeological sites and/or the anthropological record for data in support of planetary events, (e.g. asteroid or comet impacts,); 3) Industrial archaeology as it relates to planetary exploration (e.g. Apollo-era spacecraft design and the Atomic Energy Commission's Nuclear Rocket Development Station); 4) Archaeoastronomy, as historical and pre-historical astronomical artifacts relate to planetary axial orientation and pleistocene/holocene climatology; and 5) The nascent field of astrobiological xenoarchaeology, which centers on the proposed methods of investigation should ongoing planetary exploration yield evidence of astrobiological life. Recent research projects are reviewed, the implications for current planetary/archaeological research are addressed, and directions for future interdisciplinary research are discussed.
P41A-0204
Google Moon, Google Mars, and Beyond
There is a vast store of planetary geospatial data that has been collected by NASA but is difficult to access by the general public. The Google Maps API is one way to allow broad access to this data. Google Mars was the first serious effort to display high-quality planetary data within the Google Maps API, but was essentially a closed product. Users could not easily build on the Google Mars framework as has been done to great effect and diversity with the main Google Maps API for the Earth. NASA Ames Research Center and Google, Inc., are working in collaboration to provide extension capabilities to planetary data sets hosted via the Google Maps API. We are working on updates and enchancements of the existing Google Moon. Among others, we will showcase a data layer for Google Moon that provides placemarks for publications about features or regions on the Moon. These placemarks contain basic bibliographic information and links to sources of more detailed information about each publication. This layer represents a major data collection effort, and we will only have a demo version available at the meeting. The Google Maps API allows anyone to add data and build upon the existing frameworks for Google Moon and Google Mars, in the same way that is currently widely done for the main Google Maps system. Enhancing this functionality will not only enable Planetary Scientists to more easily build and share data within the scientific community, but will also provide an easy platform for public outreach and education efforts, and will easily allow anyone to layer geospatial information on top of planetary data within the Google Maps framework. In the future we hope to add additional data to Google Mars, and create Google Maps versions of other planets in the solar system, vastly increasing the public's ability to easily access NASA's store of planetary geospatial information.
P41A-0205
Evolution of Photoevaporating Protoplanetary Disks
A crucial time-scale issue in planet formation is the timing required for the loss of protoplanetary gas material, which dominates the total disk mass. The outcome for a particular planetary system might be very different if the parent disk is dispersed sooner or later than in our solar system. We model the evolution of protoplanetary disks under the influence of viscous accretion and photoevaporation by the central star. Previous studies are extended by considering the evolution of disks around different types of parent stars in which extrasolar planets have been discovered. We consider stellar masses in the range 1 to 4.7 M\sun, and extreme ultraviolet (EUV) fluxes, φ, in the range 1040 to 1043 photons s-1. The disk evolves on the viscous diffusion time scale at the gravitational radius, the disk location inside which ionized hydrogen is gravitationally bound to the central star. Photoevaporation is initially powered by the diffuse EUV flux arising from recombinations in the gravitationally bound region. Following the analysis of Alexander et al. (2007), we include the direct contribution from the direct stellar EUV flux as the gravitationally bound inner disk is removed. The disk is removed in ~30 Myr for a 4 M\sun central star and φ=1042 s-1 . Increasing the EUV flux results in shorter disk life times, as expected. Reducing the stellar mass results in shorter disk lifetimes for two reasons. First, photoevaporation is more easily accomplished since material is less tightly bound to the central star (the gravitational radius moves inward). Second, the viscous diffusion time scale at the smaller gravitational radius decreases, speeding up the overall disk evolution.
P41A-0206
The geodynamics of super-sized Earths
The habitability of a planet is strongly contingent on its tectonic regime. Recently, the discovery of giant Earth-like planets has led to speculation on their surface conditions and dynamics. Here we explore the tectonic regimes of super-sized Earths, which are a function of the balance between driving forces, and the resistive strength of the lithosphere. We use mantle convection simulations to show that simply increasing planetary radius acts to decrease the ratio of driving to resisting stresses, and thus super-sized Earths are likely to be in an episodic or stagnant lid regime. This effect is robust when associated increases in gravity are included, as the more dominant effect is increased fault strength rather than greater buoyancy forces. The thermo-tectonic evolution of large terrestrial planets is more complex than often assumed, and this has implications for the surface and conditions habitability of such worlds.
P41A-0207
The Effects of Volatile Cycyling on Planetary Thermal Evolution
The thermal history of terrestrial planets is investigated using a parameterized model that couples thermal convection and volatile cycling. The model breaks volatile inventory in two reservoirs, surface and interior, and calculates the exchange between them. A volatile-dependent mantle rheology is incorporated. We focus on water at this stage. Water recycling into the mantle is assumed to occur principally through subduction of a hydrated serpentine layer whose thickness is self-determined based on serpentine stability. Degassing occurs through magmatism which is parameterized using a volatile dependent solidus. We present preliminary results that explore model parameter space. We have also coupled a radiative-convective climate model to our mantle-volatile model to explore the feedback effects between changing climate conditions, due to mantle degassing, and volatile cycling through the mantle. The model stress state is monitored for all parameter sweeps so as to evaluate the potential of changes in the tectonic mode of a planet (plate tectonics or a single plate mode).
P41A-0208
Revisit of the Thermal Wind Equation: Application to Planetary Atmospheres at Low Latitudes
The standard thermal wind equation relates the vertical wind shear to the horizontal temperature gradient along isobaric surfaces. The relationship can be used to derive the vertical structure of wind if the temperature field is known, or vice verse. The simple-format standard thermal wind, which is based on hydrostatic and geostrophic balances, has been widely utilized in explorations of planetary atmospheres. The two balances work well for Earth's atmosphere even approaching the equator. However, the two balances behind the standard thermal wind equation should be used with caution for the equatorial regions of other planets because the large variations of jet velocities, radius, and rotation period of different planets in our solar system. Here, we examine the more general relationship between the wind field and temperature field without the hydrostatic assumption and geostrophic balance. Our thermal wind equation is tested first by a reanalysis dataset of Earth's atmosphere. Then we apply our thermal wind equation to Jupiter and Saturn, and compare with the results from the standard thermal wind equation. These comparisons suggest that our thermal wind equation is a better description for the relationship between wind and temperature fields in the equatorial regions. Another application is the derivation of the temperature field from the wind field, which is also tested by the reanalysis dataset of Earth. Furthermore, we emphasize that our thermal wind equation and the standard thermal wind equation are not at all mutually exclusive. We suggest a combination of the two equations to derive the whole zonal wind profile in the latitude- altitude cross section of planets with deep atmospheres.
P41A-0209
Modeling Hydrocarbons in the Atmosphere of Neptune and Comparison with Spitzer Observations
Recent observations made by the IRS instrument onboard Spitzer provide new constraints on the abundances of hydrocarbons in the atmosphere of Neptune. A one-dimensional, diurnally averaged photochemical model has been used to simulate the Spitzer results. We show that the molar fractions of complex hydrocarbons, such as benzene (C6H6), are extremely sensitive to the prescribed eddy diffusion profile, but simple hydrocarbons like ethane (C2H6) and acetylene (C2H2) are less sensitive to the eddy diffusivity. For example, reducing the eddy coefficients by a factor of 5 would enhance hydrocarbon abundances such as C4H2, CH3C2H, and C6H6 by more than an order of magnitude. In order to give the best fit to the methane data from Spitzer, we must enhance the concentration of methane at lower boundary over that given by Moses et al (2005). A sensitivity study with respect to the changes of eddy mixing, selected chemical reactions and CH4 concentration at the lower boundary will be presented.
P41A-0210
Planetary Magnetic Moment as Function of Mass and Rotation
I found that the planetary magnetic moment is a power law of a function of mass and rotation period.
P41A-0211
Planetary Cores Flows Driven by Mantle Libration
We investigate, via a set of laboratory and numerical experiments, the flow induced inside a spherical fluid cavity by torsional oscillation of the outer shell. Our goal is to produce models of libration-driven flows within planetary cores and subsurface oceans. Such models will improve our understanding of a number of planetary bodies including Mercury, Europa, Io, Callisto, Ganymede and the Earth's Moon. Here we focus on the case of a spherical shell with either a small inner core or no inner core; moderate planetary rotation rate (Ekman number E = 10- 4); and libration frequency equal to the planetary rotation frequency ("synchronous libration"). We vary only the non-dimensional amplitude of libration α, defined as α=Δ φ (2 π flib) / Ømega, where Δ φ is the total angular displacement, flib is the libration frequency and Ømega is the background angular rotation rate. Different core flow regimes are observed as α is increased. For a small amplitude of libration (α \ll 1)), the oscillatory motion of the outer boundary drives laminar flows that are well described as inertial modes and waves. For α ~ 0.5, azimuthal roll instabilities periodically develop and decay along the outer shell boundary during each libration cycle. These instabilities tend to develop when the outer shell is decelerating and decay when it is accelerating. By further increasing α, the flow pattern transitions from axisymmetric rolls (m=0) to wavy rolls (m ≠ 0), and then to turbulent flow. Extrapolating our present results to Mercury suggests that mantle libration can drive large-scale instabilities in its liquid metal core. The authors wish to the thank NASA's PG&G and PME Programs for reasearch funding under grant #NNG0697G.
P41A-0212
Life Between The Stars: Could Tidal Heating Produce More Biology Than Starshine?
The search for life in the universe should not be confined to terrestrial planets; in fact it may not even be the best place to look. Tidally energized, ice-capped ocean worlds like Jupiter's moon Europa may be a more common home for carbon-based, aqueous life forms. Europan satellites can orbit giant planets and brown dwarfs, both of which appear to be relatively abundant. Moreover, since they do not require starlight for energy, they can inhabit a much greater volume of space. This raises the question as to whether tidally energized satellites are orbiting brown dwarfs within our Sun's gravitational sphere of influence. Theoretical and observational evidence indicates that brown dwarfs could be orbiting Sol at distances out to 100,000 A.U. or more. The possibility of finding these distant circumsolar objects is explored by comparing some of their predicted characteristics and our ability to detect them. A study of the circumsolar brown dwarf population beyond 100 A.U. may now be feasible, particularly at infrared wavelengths. Such an exercise could reveal new worlds to explore and new insights regarding the general characteristics and relative abundance of tidally energized biology in the universe.
P41A-0213
A Physical Model For Thermal Evolution And Metal Segregation In Early Planetesimals
Early core formation in planetesimals has been known for a long time from the existence of iron meteorites, however, the physical processes leading to core segregation are still a matter of debate. Until recently, the percolation of iron metal melt within a silicate solid matrix had not been considered because of the very high dihedral angle and because melting of silicate is often assumed necessary. Some recent studies have shown that iron metal melts migrate in a solid silicate matrix even at low porosity (e.g. Yoshino et al, 2003). We investigate the melting and percolation of iron-sulfide metal melts within a solid silicate matrix and its application to planetesimals using a spherically symmetric two-phase flow model coupled to the heat equation. The heat source for melting are the short-lived radionuclides (26Al and 60Fe). When the Fe-S eutectic is reached, percolation can start and metallic melt migrates to the center of the planetesimal due to the planetesimal's own gravity. We propose a complete model for segregation and obtain the resulting thermal state of the differentiated planetesimal. The short half life of both 26Al and 60Fe allows us to estimate a timescale for differenciation in the solar system. The varying degrees of differentiation of the different objects can be investigated within this framework. The case of icy satellites may be treated with the same approach and the largely undifferentiated nature of Callisto (one of Jupiter's largest satellites) can be used to constrain the conditions of its formation.
P41A-0214
Chemistry of Earth's Putative Steam Atmosphere
The concept of a steam atmosphere generated by impact devolatilization of planetesimals accreted during Earth's formation is over 20 years old (Matsui and Abe, 1986; Lange and Ahrens, 1982). Surprisingly, with the possible exception of a few qualitative remarks, no one has critically assessed this scenario. We use thermochemical equilibrium and, where relevant, thermochemical kinetic calculations to model the chemistry of the "steam" atmosphere produced by impact volatilization of different types of accreting material. We present results for our nominal conditions (1500 K, total P = 100 bar). We also studied the effects of variable temperature and total pressure. The composition of the accreting material is modeled using average compositions of the Orgueil CI chondrite, the Murchison CM2 chondrite, the Allende CV3 chondrite, average ordinary (H, L, LL) chondrites, and average enstatite (EH, EL) chondrites. The major gases released from CI and CM chondritic material are H2O, CO2, H2, H2S, CO, CH4, and SO2 in decreasing order of abundance. About 10% of the atmosphere is CO2. The major gases released from CV chondritic material are CO2, H2O, CO, H2, and SO2 in decreasing order of abundance. About 20% of the total atmosphere is steam. The major gases released from average ordinary chondritic material are H2, CO, H2O, CO2, CH4, H2S, and N2 in decreasing order of abundance. The "steam" atmosphere is predominantly H2 + CO with steam being about 10% of the total atmosphere. The major gases released from EH chondritic material are H2, CO, H2O, CO2, N2, and CH4 in decreasing order of abundance. The "steam" atmosphere is predominantly H2 + CO with about 10% of the total atmosphere as steam. This work was supported by the NASA Astrobiology and Origins Programs.
P41A-0215
Experimental simulation of organic matter alteration in carbonaceous chondrites under an in situ micro FTIR spectroscopy
Carbonaceous chondrites contain organic matter up to a few weight percents, most of which consists of kerogen- like macromolecular material. Chondritic organic matter preserves signatures of various evolutional steps from presolar materials, through aqueous alteration and thermal metamorphism in the parent asteroid up to delivery to the Earth. The organic-mineral interactions during these processes are little known. We report here on the experimental simulation of organic matter alteration on carbonaceous chondrite parent body under micro FTIR spectroscopy with a heating stage. Leonardite humic acid (IHSS standard humic acid) and synthetic saponite or natural antigorite were used as the macromolecular organic matter and the matrix mineral. These powdered samples were dispersed by MilliQ water then dropped on a CaF2 plate and dried. They were heated in the heating stage from room temperature to 600 oC with a heating rate of 10 oC/min in air, Ar gas, and H2+CO2 gas mixture (mixing ratio 1:1). H2+CO2 gas mixture enables controls of not only oxygen fugacity but also water vapor fugacity, and aqueous processing on chondrite parent bodies can be partly simulated. IR spectra were collected at every 20 oC under the micro FTIR spectroscopy. Aliphatic C-H increased from room temperature to approximately 250 oC then decreased. Aromatic C-H increased from room temperature to around 400-450 oC then decreased. These aliphatic C-H decrease and aromatic C-H increase are faster in air than in Ar or H2+CO2. These CH changes of leonardite humic acid are slower with the presence of saponite. These results indicate that organic matter transformation might be prevented by the clay mineral (saponite). Some carbonaceous chondrite samples mixed with the organic material (leonardite humic acid) will also be investigated by the same way. These results will elucidate interactions of chondritic macromolecular organic matter with matrix minerals during parent body processes.
P41A-0216
Petrography and Mineralogy of a Unique Spherical CAI in the Murchison (CM2) meteorite
Chondritic meteorite consist of three major components: refractory CAIs, less refractory ferromagnesian silicate spherules called chondrules, and a fine-grained matrix. It is generally believed that CAIs and chondrules formed in the solar nebula (a disk of dust and gas surrounding the proto-Sun) by high-temperature processes that included condensation, evaporation, and for all chondrules and many CAIs, subsequent melting during multiple brief heating episodes (1). Calcium-aluminum-rich inclusions (CAIs) from chondritic meteorites are widely considered to represent the first materials that formed in the solar nebula (2). I discovered for the first time a unique spherical CAI, which consist of spinel, diopside, calcite, and PCP in the Murchison (CM2) meteorite. The unique spherical CAI seems to be surrounded amoeboidal materials. Its size is approximately 1.5mm and this is large when comparing with the average size of chondrules in the all chondrites. Its shape is like chondrules, but fusion organization which is characteristic of chondrules is denied by absence of the glass and mesostasis. The whole area of the unique spherical CAI , it can see abundant void spaces. The unique spherical CAI never melts after the formation. Also, bulk composition is similar to Ca-Al-rich chondrules discovered in ordinary chondrites, or CAI of CV carbonaceous chondrite. Comparison with normal CAI, its may be generated from different formation processes. The inside of the unique spherical CAI, spinel, diopside, calcite and PCP coexist each other. Replacement is not seen. Therefore, the unique CAI is thought to be mixture of high temperature condensation minerals and low temperature materials as well as PCP in the early solar nebula. A recent study suggests that carbonate may form as a result of non-equilibrium condensation in the presence of water vapor in circumstellar environments (3). The textual occurrences of calcite in the unique spherical CAI are clearly compatible with such a scenario. References 1. MacPherson G. J. et al., Meteorites and the Early Solar System, 746-808 (1988) 2. Allegre C. J. et al., Geochim. et Cosmochim. Acta 59, 1445-1456 (1995) 3. Toppani A. et al., Nature 437, 1121-1124 (2005)
P41A-0217
Unusually High Abundance of Silica Phases in Chondrules In a CR Chondrite, NWA852
Carbonaceous chondrites are the most primitive material in the solar system. A study of chondrules should shed light on the formation conditions of the solar system 4.56 Ga ago. In this study, we measured petrographical properties of 47 chondrules in NWA852 (CR2). Their apparent diameters range from 0.19mm to 2.82mm. The mean diameter is 0.75mm. The density of chondrule is 1.65 /mm2, and they occupy 80 vol. % in the thin section studied here. This is much larger than the mean chondrule abundance, 50-60 vol. %, for CR (Scott et al., 1996). Their textures are divided into 5 types. Porphyritic Olivine-Pyroxene(POP) (63.8 %), Porphyritic Olivine (PO) (14.9 %), Porphyritic Pyroxene (PP) (14.9 %), and Granular Olivine-Pyroxene (GOP) (2.1 %). Thus, pyroxene-bearing chondrules are abundant in NWA852. There are also two compound chondrules (4.3 %), consisting of BO and POP, and PO and BO, respectively. The shapes of chondrules are irregular (66.7 %), round (23.3 %), and ellipsoidal (10.0 %). Several CAIs are also found in this sample. Silica phases have been already reported from CR chondrites (Krot et al., 2002; Campbell et al., 2005). We also found silica phases from chondrules in NWA852. However, abundance in NWA852 is unusually high. About 30 % of the chondrules contain silica phases, typically in their peripheral parts. The common occurrence of silica phases in the chondrules might be related to the high amount of pyroxene, and might be a key to understand the nebular fractionation. Keywords: CR chondrite, chondrule, pyroxene, silica M. Tabata: a7sm6030@ganko.tohoku.ac.jp
P41A-0218
Molecular Identification of the Deuterium-Rich Carrier in Insoluble Organic Matter in Carbonaceous Chondrites
Insoluble organic matter (IOM) in primitive carbonaceous chondrites is known to be enriched in deuterium, with D/H ratios > 300×10 -6. It is also characterized by a high degree of isotopic heterogeneity, as demonstrated by the observation of D-rich "hot spots" in NanoSIMS ion microprobe images [1] and by GC-irMS studies [2]. Understanding the origin of this heterogeneity represents a fundamental challenge with implications for the origin and distribution of organics in the interstellar medium and in the protoplanetary disk from which our planetary system formed. We have determined the carrier of the isotopically anomalous hydrogen in IOM isolated from the carbonaceous chondrite Orgueil. Electron Paramagnetic Resonance spectroscopy has shown that hydrogen in the benzylic bond of organic radicals has a deuterium to hydrogen (D/H) ratio of 1.5±0.5×10-2 in Orgueil IOM, which is the highest solar system D/H ratio ever reported [3]. By combining these data with quantitative image analysis recorded at a high spatial resolution with the NanoSIMS, we are able to prove that the organic radicals can account for the deuterium excess in the IOM D-rich "hot spots". Furthermore, the radicals fall on a well-defined trend between D/H ratio and C-H bond energy [2], consistent with a new interpretation of the hydrogen isotopic variations in solar system organics according to which pre-existing organics exchange their D with highly deuterated gaseous molecules, such as H2D+ or HD2+. The distributions of these deuterated species has been theoritically mapped in protostellar disks [4]. This conclusion runs contrary to previous interpretations, according to which the IOM is an interstellar product reprocessed in the protosolar gas and deuterium-rich "hot spot" relics of pristine interstellar organic matter, which escaped solar nebula or parent body processes. [1] Busemann et al (2006) Science 312, 727-730; [2] Remusat L. et al. (2006) Earth Planet. Sci. Let. 243, 15-25 ; [3] Delpoux O. et al. (2007) 38th LPSC, #1138. [4] Ceccarelli C. and Dominik C. (2005) A&A 440, 583-593.
P41A-0219
Primary Ferric Iron-Bearing Rhönite in Plutonic Igneous Angrite NWA 4590: Implications for Redox Conditions on the Angrite Parent Body
Northwest Africa 4590 is a heterogeneous olivine gabbro with cumulate texture composed of Al-Ti-rich clinopyroxene, pure anorthite, Ca-rich olivine, kirschsteinite and ulvöspinel, with accessory troilite, merrillite, Ca silicophosphate, kamacite and glasses [1]. Rhönite now has been identified in this specimen (for the first time in any angrite) as (1) a large (0.65 mm long), blocky, anhedral grain adjacent to anorthite, kirschsteinite and troilite, (2) ca. 15 micron grains along grain boundaries of the major phases (in one case in contact with clinopyroxene and metal), and (3) ca. 30 micron grains within melt inclusions and veins composed of kirschsteinite, olivine, anorthite, troilite, hercynite and glass. The rhönite is nearly opaque in transmitted light, with a deep cinnamon-red color on thin grain edges. The average composition of the largest grain is (in wt.%): SiO2 23.6, TiO2 9.9, Al2O3 16.3, Cr2O3 0.1, FeOt 33.6, MnO 0.14, MgO 3.5, CaO 13.1. Stoichiometry (14 cations, 20 oxygen atoms) requires about 12% of the total iron to be in the ferric state, resulting in the nominal formula: (Ca2.01Mn0.02)(Fe2+3.55Fe3+0.45Mg0.75Al0.12Cr0.15)Ti0.9 5(Si3.37Al2.63)O20 In the co-existing ulvöspinel about 18% of the iron must be ferric to achieve charge balance; likewise, Fe-Ti spinel coexisting with metal in Angra dos Reis contains ferric iron [2]. In contrast, the spinel (Cr-pleonaste) in metal-rich angrite NWA 2999 is stoichiometric without any apparent ferric iron. The coexistence of ferric iron- bearing silicate and oxide phases with Fe metal implies that the oxygen fugacity during crystallization of NWA 4590 was somewhat more oxidizing than that of the IW buffer. Compositions of primary (pre-exsolution) olivine and kirschsteinite in NWA 4590 record a minimum magmatic temperature of 910-950°C, based on the solvus of [3]. Previous experimental studies [4] also imply that other metal-bearing plutonic (AdoR, LEW 86010) and quench-textured (LEW 87051) angrites equilibrated at oxygen fugacities near QFM - 2 log units and relatively high temperatures. Although not previously known from angrites, rhönite has been reported from terrestrial alkalic rocks, CV chondrites and a lunar mare basalt [5]. [1] Irving A. et al. (2006) EOS, Trans. AGU 87, #P51E-1245; Kuehner S. and Irving A. (2007) LPS XXXVIII, #1344 [2] Prinz M. et al. (1977) EPSL 35, 317-330 [3] Mukhopadhyay D. and Lindsley D. (1983) Amer. Mineral. 68, 1089-1094 [4] Jurewicz A. et al. (1991) Science 252, 695-698; McKay G. et al. (1994) GCA 58, 2911-2919 [5] Treiman A. (2007) LPS XXXVIII, #1244.
P41A-0220
Determining the Origin of Phosphates in Lherzolitic Shergottites Through Phosphate Saturation Experiments
Phosphorous has been correlated with sulfur and chlorine in martian soils with some soils containing several wt % P2O5 and high-P2O5 layer covers many rocks. However, using the RAT to remove the top few mm of some rocks revealed zones of low-P2O5 in the outer mm relative to the interior composition. This suggests that some igneous rocks of Mars are high in P2O5 and that over time phosphorous has been mobilized into the martian soils. In martian meteorites, phosphorous has been detected in high concentrations relative to terrestrial basalts and cumulates. High intensity x-ray maps of lherzolitic shergottite ALH 77005 reveal phosphates in olivine-hosted melt inclusions and P2O5 zoning in the host-olivine. Analyses of rehomogenized olivine-hosted melt inclusions reveal high-P2O5 glasses (>5 wt %). As phosphates are the major reservoir of REE in martian meteorites, determining if the phosphates are primary igneous or secondary sedimentary minerals may have significant consequences for use of REE as oxybarometers and radiogenic-isotopic dating systems in these meteorites. Therefore, an experimental investigation was initiated to determine whether the phosphates are primary igneous minerals or secondary weathering products. The phosphate saturation curve in SNC magmatic compositions has been studied experimentally by synthesizing the parental melt composition of lherzolitic shergottite ALH 77005 and performing anhydrous crystallization experiments in TZM pressure vessels. The parental melt composition was then doped with 5 wt % P2O5 in the form of CaHPO4 and the crystallization experiments were repeated. ALH 77005's parental melt saturated phosphate near 7 wt % at 1165°C and 5 wt % at 1150°C. These saturation values illustrate how high-P2O5 would have to build up before phosphates would nucleate and are consistent with high-2O5 content found in rehomogenized olivine-hosted melt inclusions. These saturation values are higher than the reported saturation for lunar and typical terrestrial basalts, which may reflect differences in the composition, volatile content, and/or the oxidation state of shergottite magmas. The presence of phosphate-saturated melts in rehomogenized, olivine-hosted melt inclusions suggests that olivine contains previously unaccounted for high levels of phosphate. If the phosphates are magmatic in origin, the evidence suggests that phosphates saturated earlier in the crystallization of lherzolitic shergottite ALH 77005 than previous authors have indicated and therefore phosphates contained in olivines have a larger impact on REE evolution of the magma than if olivine had been crystallizing alone. If the included phosphates are secondary in origin, the presence of enough P2O5 to saturate a melt inclusion with phosphate during rehomogenization suggests that mineral separates of olivine would still carry enough REE to have a significant effect on studies that attempt to use REE for oxybarometers and radiogenic-isotopic dating.
P41A-0221
The NEAT database photometry and constraints on the rotation of 5535 AnneFrank.
In November of 2002, the main belt asteroid 5535 Annefrank was observed over a 26-minute window with the Stardust spacecraft. During this time, the first spacecraft images of this S-class asteroid were taken over ~40% of the surface at a resolution of 185-300 m/pixel (Duxbury et al. 2004). Stardust collected 72 images at varying phase angles, producing a phase curve out to 134 degrees and a geometric albedo of 0.24. Annefrank's orientation, shape and size were constrained by the encounter's imaging data, revealing a minimum triaxial ellipsoid size of 6.6 x 5.0 x 3.4 km, and irregular topography, including a protrusion along the end of its longest axis. Owing to the brevity of the observing window no constraints on the rotational period or spin axis orientation were made by the encounter, and Annefrank is assumed to be a slow-rotator. Thus, we began a campaign to observe Annefrank in May of 2005 through December of 2006 using the 0.6 meter telescope at Table Mountain Observatory, run by Caltech's/Jet Propulsion Laboratory (JPL). A total of 14 nights of observation yielded a light curve with possible rotational periods of 0.48, 0.63, and 0.95 days, so that further constrains were required to determine its rotation and spin axis orientation. The Near-Earth Asteroid Tracking (NEAT) project at JPL has systematically observed the sky for more than a decade. While the main objective of NEAT is the discovery of near-earth objects (NEOs), the NEAT database provides multiple observations over varying time scales (hours, days, months and years). As a result, the NEAT database provides a history of behavior over a time span of more than ten years and can serve as a powerful tool to analyze the time-dependent nature of solar system bodies. We use the NEAT database here to conduct a photometric study of 5535 Annefrank to better constrain the period and derive an orientation of the spin axis. The data have also been used to conduct photometry and derive phase curves of bright outer solar system objects, and we present a subset of these results as well. This research was funded in part by NASA through the Discovery Data Analysis Program. This work was performed in part at the Jet Propulsion Laboratory operated by the California Institute of Technology under contract with NASA.
P41A-0222
Shape, Topography and Roughness of 25143 Itokawa
The recent visit of the Hayabusa spacecraft to the small near-Earth asteroid (NEA) 25143 Itokawa yielded the surprising discovery that Itokawa was not an intact object but a low density, gravitationally accumulated, rubble pile. This contrasts with the finding, from the only other NEA visited by an asteroid lander, that 433 Eros was an intact object and not a rubble pile. Eros was visited by the NEAR Shoemaker spacecraft which landed in 2001. Accurately co-registered, high resolution imager and lidar data from NEAR Shoemaker have demonstrated the fractal properties of small scale surface topography on Eros, where boulders tend to be found on the tops of long ridges, consistent with the presence of an underlying globally coherent structure. However, Itokawa is a rubble pile with a fundamentally different collisional history. Here we analyze co-registered, high resolution lidar and imager data from Itokawa, obtained by Hayabusa, to explore fractal properties and surface roughness distributions on Itokawa for comparison with the results from Eros.
P41A-0223
Elemental Composition of 433 Eros: New Calibration of the NEAR-Shoemaker XRS Data
We present the results of a new calibration of the elemental-abundance data of the asteroid 433~Eros taken by the X-ray Spectrometer (XRS) aboard the NEAR-Shoemaker spacecraft, which orbited Eros from 2000--2001. The XRS measured solar-induced X-ray fluorescence from the top 100~μm of the surface of Eros. The relationship of the measured fluorescence line ratios to asteroidal elemental abundance ratios is critically dependent on the incident solar X-ray spectrum, which varies rapidly in time. The data from NEAR's surviving onboard solar monitor proved difficult to calibrate, and the previously published elemental results [1] relied on an imperfect preliminary calibration that resulted in significant and incompletely characterized systematic uncertainties. The solar monitor response and associated uncertainties have now been characterized by cross-calibration of a large sample of NEAR solar flight data against contemporary broadband solar X-ray data from the GOES-8 satellite. The results have been used to produce new X-ray spectra and errors for eight major solar flares (five of which were covered in [1]) during which the NEAR XRS collected data from 433~Eros. The revised surface elemental ratios for 433~Eros include new error estimates that accurately reflect the remaining uncertainties in the solar flare spectra. The new elemental ratios fall within the cited uncertainties of the previous results [1]. and are therefore consistent with the conclusions [1,2] that 433~Eros has an ordinary chondritic composition altered in S/Si and possibly Fe/Si at the surface by space weathering. The 1--10 keV NEAR solar X-ray spectra were successfully matched by a two-temperature model using isothermal components generated by the CHIANTI code [3]. This approach may be applicable to the analysis of data from the Hayabusa XRS, particularly in the analysis of the S/Si ratio, since Hayabusa's onboard standard lacked sulfur [4]. This will enable comparison of Itokawa's S/Si value with Eros' highly depleted S/Si. This approach may also be helpful in analysis of data from the MESSENGER XRS. [1] Nittler et al.~(2001) M&PS 36, 1673. [2] Foley et al.~(2006) Icarus 184, 338. [3] Landi et al.~(2006) ApJS 162, 261. [4] Okada et al.~(2006) Science 312, 1338.
P41A-0224
Planetary Scale Impacts and Consequences for the Mars Hemispheric Dichotomy
Planetary-scale impacts are events in which the resultant impact basin is a significant fraction of the planet's circumference. The curvature of the planet is expected to be important in the impact process, especially as it relates to the fate of downrange ejecta in off-axis events. Planetary-scale impacts are abundant in the Solar System, especially early in its evolution. A possible candidate planetary-scale impact basin is the Martian hemispheric dichotomy, expressed as a difference in surface elevation, crustal thickness, and surface age between the northern lowlands and the southern highlands. We investigate the characteristics of planetary-scale impacts, and in particular the effects of a mega impact on Mars. We use a 3 dimensional self-gravitational Smoothed Particle Hydrodynamics (SPH) model to simulate the impacts, implementing an olivine equation of state derived for the Tillotson formulation, and use this to establish the initial pressure and internal energy profile of the planet. The parameter space of impactor energy, impactor size, and impact velocity are explored for Mars hemispheric impacts. We find that for a given impact energy, head-on large but slow impacts produce more melt and cover more of the planet with melt than small, fast, and oblique events. Head-on impacts produce crustal blow-off and a melt pool at the antipode. Oblique impacts do not cover much of the planet with melt, but create sizable basins. Various degrees of crustal thickening are apparent around the crater over a length of ~1000 km; this crustal thickening could relax over geological time. Fast impacts eject material with escape velocity many times their own mass. In all cases, less than 10% of the impactor's mass is placed in orbit. For oblique events, a significant fraction of the angular momentum in the system is carried away by escaping material, limiting the efficiency of angular momentum transfer to the planet.
P41A-0225
Chemical Aspects of the Impact Process
Impact cratering plays an integral role in the evolution and formation of planetary systems. Chemical anomalies are accepted phenomena at impact sites, but few, if any, published models adequately describe the kinetics and thermodynamics of impact-induced chemical changes. Utilizing XRF, ICP-MS, GDMS,and SHIRMP-RG, this study analyzed the trace chemical composition of shock- metamorphosed granite and obtained quantitative data, which were further analyzed using parametric frequentist statistics and resampling techniques. The concentrations of Cu, Ni, Pb, Zn, Rb, and Sc changed in a statistically significant manner at the 99% confidence level. Based on chemical and thin section analyses, a cohesive model was developed to describe how impact-induced chemical changes form. As the impactor collides with the target material, most of the impactor melts. As the shock waves and subsequent rarefaction waves move through the target, partial melting of mineral phases begins. Material from the impacting body combines with the partial melt, thereby amalgamating an extraterrestrial component into the target. Characteristics of the amalgamation process are related to the partitioning coefficients, ionic radii, ionic charges, and electron configurations of the involved components. Ongoing work focuses on the determination of the relationship between chemical composition and proximity to interstitial boundaries.
P41A-0226
Validation of the RAGE Hydrocode for Impacts into Volatile-Rich Targets
In preparation for a detailed study of large-scale impacts into the Martian surface, we have validated the RAGE hydrocode (Gittings et al., in press, CSD) against a suite of experiments and statistical models. We present comparisons of hydrocode models to centimeter-scale gas gun impacts (Nakazawa et al. 2002), an underground nuclear test (Perret, 1971), and crater scaling laws (Holsapple 1993, O'Keefe and Ahrens 1993). We have also conducted model convergence and uncertainty analyses which will be presented. Results to date are encouraging for our current model goals, and indicate areas where the hydrocode may be extended in the future. This validation work is focused on questions related to the specific problem of large impacts into volatile-rich targets. The overall goal of this effort is to be able to realistically model large-scale Noachian, and possibly post- Noachian, impacts on Mars not so much to model the crater morphology as to understand the evolution of target volatiles in the post-impact regime, to explore how large craters might set the stage for post-impact hydro- geologic evolution both locally (in the crater subsurface) and globally, due to the redistribution of volatiles from the surface and subsurface into the atmosphere. This work is performed under the auspices of IGPP and the DOE at LANL under contracts W-7405-ENG-36 and DE-AC52-06NA25396. Effort by DK and EA is sponsored by NASA's Mars Fundamental Research Program.
P41A-0227
Implications of a Caldera Origin of the Lunar Crater Copernicus
The forthcoming renaissance in lunar exploration will focus on many objectives such as Copernicus. Copernicus appears to be a caldera for at least 8 reasons. If a caldera we see (1) transient activity (2) no overturned impact flap at the crater margins (3) internal sinuous leveed lava flow channels (4) a lava covered floor (5) terraces of different ages (6) multiple central volcanoes, one showing a directed volcanic blast (7) olivine-rich komatiitic lavas on central volcanoes and (8) magmatic inflation/deflation on caldera flanks localizing craterlets and extinct fumaroles in "loop" patterns. Regarding (6), directed volcanic blasts can remove a segment of the volcano wall as evidenced in terrestrial analogs at Mt. St. Helens and Bezymianny. Impact mechanisms to produce this feature in Copernicus are contrived. For (7) Clementine spectral data show a high olivine content of the central mountains on Copernicus which I interpret as forsteritic spinifex mineralization in komatiitic lavas and not as impact rebound of olivine-rich deep seated rocks. (8) MacDonald (1956) documented loop patterns on the flank of Halemaumau in Hawaii defining arcuate fractures localizing fumaroles and craterlets. Inflation/deflation of subjacent magma bodies are interpreted as the cause for these loops. Inflation/deflation mechanisms on caldera flanks are common around terrestrial calderas. "Loop" patterns on the flank of Copernicus localizing "gouge" craterlets have been interpreted as ballistic features resulting from the meteorite impact of this crater. Questioned is the logic of a linear N26E trending array of fragments within Copernicus to serve as a source of ballistic projectiles to form the loops localizing conjugate craterlets. The fused craterlet axes on the lunar loops do not point back to a presumed impact center in Copernicus. The axes are oriented parallel to a regional northwest (N35-60W) fracture zone. Implications for an endogenic origin of Copernicus would involve revisions of lunar stratigraphy. The origin of major rayed craters would also require review. The breached central volcano would offer a unique exploration objective. Hydrothermal alteration on the interior walls of the volcano should be accessible. Permanently shadowed zones at 40 K and near surface layers within the volcano could retain pockets of Precambrian fumarolic ices such as carbon and sulfur-bearing fluids, chlorine, methane, formaldehyde, nitrogen, ammonia, ammonium cyanide and water. A major implication would be possibility of biomarkers of Precambrian protolife. Energies for the creation of protolife would be electrical potentials created by flow charging or, on freezing, by charge separation. Well documented progressions from racemic amino acids formed "in the spark" (and stabilized by volcanic ammonium borate) reacting with adenine (formed in part by cooling ammonium cyanide) yield adenosine. The latter in turn can react with water-soluble volcanic polyphosphates to form adenosine triphosphate. Trace amounts of fumarolic tungsten could create tungstoenzymes as catalysts. Fischer-Tropsch catalysis could also generate lipid micelles and polycyclic amino acids. A critical prebiotic compound, formic acid, can be formed from troilite (a relatively common lunar iron sulfide) in an aqueous solution with hydrogen sulfide and carbon dioxide. The reaction is thermodynamically viable with a free energy of -11.9 kj/mole. Special physical attributes of fumaroles, such as spatter, involve wet/dry cycles and a version of a polymerase chain reaction creating an exponential replication of nucleotides. Copernicus as a caldera offers a significant role in both robotic and human exploration.