P31A-1377
Irreversible Evolution of the Terrestrial Planets according to Geological and Petrological Data
How the terrestrial planetary bodies were developed? We discuss these problems on examples of the Earth and the Moon, which evolution studied the best. According to modern views, after accretion of the bodies, magma oceans of some hundreds km deep appeared on their surface. According to Jeffries (1929), solidification of large molted bodies, because of the difference between adiabatic gradient in silicate melts (0.3°C/km) and gradient of their melting points (3°C/km), could be going only upwards, from the bottom to the surface. As a result, a powerful crystallizing differentiation of the oceans' magmas led to accumulation of the most low-melting components on their surfaces. Due to different oceans deep, the primordial crusts on these bodies were rather different: sialic on the Earth and basic on the Moon. Geological evolution of the Earth began ~4 Ga ago from appearance of granite-greenstone terranes (GGT) and divided them granulite belts. Magmatism of high-Mg komatiite-basaltic series was located in greenstone belts, which formed irregular network within GGTs. They were formed above mantle superplumes of the first generation, composed by depleted (due to directed solidification of the magma ocean) ultramafic material; granulite belts were formed on places of descending mantle flows. The situation could be described in terms of plume- tectonics. By the 2.7-2.5 Ga the Earth's crust became cratonized and magmas of siliceous high-Mg series (SHMS) began predominate. Origin of the SHMS was linked with large-scale assimilation of lower crustal material by high-temperature mantle-derived magmas. Cardinal change of tectonomagmatic activity occurred 2.3-2.0 Ga with appearance in global scale of geochemical-enriched Fe-Ti picrites and basalts, typical for Phanerozoic within-plate magmatism and linked with mantle plumes of the second generation, which ascended from the liquid core-mantle boundary (CMB). It was followed by plate tectonic appearance ~2 Ga and such tectonic regime has existed till now. From this particular time, ancient Earth's continental crust began to involved in subduction processes and has replaced by secondary oceanic crust which forms about 70% of the present-day crust. We suggest that such situation could be possible only in case when (1) accretion of the Earth was heterogeneous, and (2) it's warming occurred downwards, from surface to core. It could be a result of moving inwards a wave of deformations, accompanied by emission of heat. Appearance of such wave could be linked with gradual compaction of material which led to acceleration of the Earth's rotation around axis. At the first stage the wave went through depleted mantle and led to appearance of mantle superplumes of the first generation. At the second stage it reached and melted iron core. It led to appearance of mantle superplumes of the second generation (thermochemical), enriched in fluids, Fe, Ti, and incompatible elements. Material of such superplumes reached more shallow levels, which led to active interactions of their extended heads with solid lithosphere and caused changing in tectonic activity. Terrestrial planets were developed at the same, but shortened scenario. At the Moon the earliest magmatism of highlands were close to terrestrial SHMS and at the boundary 3.9-3.8 Ga ago was changed by maria magmatism, close in composition to MORB and OIB. By analogy with the Earth, we suggest that maria magmatism was linked with ascending of thermochemical superplumes, generated at the lunar CMB, when it's liquid iron core was yet existed. Ancient planums on Mars and tesseras on Venus among vast planides, composed by basaltic flows, can also evidence about two stages of their development.
P31A-1378
Stability of the Solar System
It is a well established myth that the solar system is stable. The argument is generally based on the fact that the rate of the radiative plus solar wind mass loss of the Sun has a relatively small value of 8.81E-05 (1/Byr = 1/Ma) (radiative: 6.63E-05 (1/By)). Experimental results, e.g., that the Earth is separating from the Sun (10m/100year)(1), put the concept of stability of solar planetary orbits into doubt. An understanding of the stability of the solar system is a critical step towards the understanding of the stability of galaxies and the Universe.(2,3) The stability of planetary orbits, which is the other factor determining the stability of the solar system, has until recently not been modeled.(4) A model is presented which shows that the planetary orbits are weakly bound relative to orbital separation, ranging from 0.6 percent for Mercury to 0.006 for Pluto, and 0.0011 percent for CR105, the furthest reported planetesimal. These values are in the order of solar mass/gravity loss, and as a consequence, the model predicts that the solar system is expanding since its formation. The present separation rate of Earth is calculated to 3.0 m/year. Eventually orbital separation of planets will occur, e.g., at 133.8, 1.30, and 0.23 Billion years for Mercury, Pluto, Cr105, respectively under current conditions. The model shows that Mars was previously closer to the Sun and exposed to higher radiation, and that the transition from water to ice on its surface occurred 3.6 Billion years ago.(4) Predictions of the model are reported for all planets and dwarf planets. References: 1. C. Laemmerzahl, 2006, 70th Annual Meeting, German Physical Society, (DPG); Note: indirect measurements, quote: ‚The cause for the drifting apart of Sun and Earth cannot be explained by present knowledge and methods of gravitation physics' 2. I. H. Leubner, 2003, 'The Formation of the universe (Big Bang) as a Crystallization Process', Rochester Academy of Science, 30th Fall Paper Session, November 15, 2003, College of Science, Rochester Institute of Technology 3. I. H. Leubner, 2008, 'Derivation of the Hubble Constant' 35th Annual Fall Scientific Paper Session, Rochester Academy of Science Nazareth College, Rochester, NY, November 1, 2008 4. I. H. Leubner, 2004, 'Mars Orbit and Temperature: Why and When an Early wet Mars', AGU Fall Meeting, Session P01, #82
P31A-1379
Transformation of Tidal Deformations into Geodynamic Processes and Fractal Rheology of the Earth's Substance
The kinematics and dynamics of a binary "Earth-Moon" planet system have been studied with respect to the rotational motion of the Earth and Moon about the barycenter of the system, situated at a distance of 4641 km from the center of the Earth. The Earth's orbital motion, rotation and tidal deformations have a significant influence on the geodynamic processes, generation and support of the magnetic field, and climate changes of the planet. It has been shown that the tidal force causes displacements of the inner core; the corresponding gravitational effect on the Earth's surface has been evaluated (Avsyuk, 2001; Avsyuk, Suvorova, 2006). To explain these correlations, a number of mechanisms of transformations of radial tidal deformations into lateral displacements of the Earth's substance have been considered. In addition, three rheological models were taken to model tidal deformations: viscous, granular, and a fractal model based on Zener's standard rheological element. Mathematical modeling of tidal deformations for different rheologies of the substances of Earth demonstrated that the radial planetary tides are being transformed into lateral motion of planetary layers. Evaluation of the rate of lateral motion shows that this mechanism can be responsible for the westward drift of the lithosphere. The rate of lateral motion of planetary layers depends on the magnitude of the rate of radial tidal deformations, k(r). Mathematical modeling of tidal deformations for different distributions k(r) showed that the radial variation of this coefficient produces differential motion of deep planetary layers resulting in internal frictional heating of deep layers which can raise temperatures at given depths to the melting point of this material (Maslov, Anokhin, 2007; Maslov, 2007). This melting can be one of the factors influencing and amplifying the Earth's magnetic field. It is shown that the rate and energy of differential lateral motion of material in the core are enough to generate and support Earth's magnetic field. Experimental modeling (Revuzhenko, 2006) of tidal deformations in granular substance is in good agreement with the results of mathematical modeling.
P31A-1380
Orbital and Mass Evolution of Planets Undergoing Run-Away Gas Accretion
We have analyzed the orbital and mass evolution of planets that undergo run-away gas accretion in a circumstellar disk by means of high-resolution, three-dimensional hydrodynamics simulations. The radial distribution of the disk torque per unit disk mass provides an important diagnostic for the nature of the disk-planet interactions. We first show that torque distributions for nonmigrating planets of fixed mass are in general agreement with the expectations of resonance theory. We then present results of calculations for migrating, mass-gaining planets. Our main findings are: (1) For planets with an initial mass Mp=5 Earth masses, which are embedded in disks with standard parameters (aspect ratio h~ 0.04--0.05 and alpha-viscosity ~ 0.001--0.1) and which undergo run-away gas accretion growth to one Jupiter mass, the torque distributions per unit disk mass are largely unaffected by migration and accretion for a given planet mass. The migration rates of these planets are in agreement with the predictions of the standard theory for planet migration (Type I and Type II migration). In the intermediate and Jupiter-mass regimes, migration rates can be accounted for by standard Type I theory, corrected for the gas depletion in the gap region. (2) The planet mass growth rate is dMp/dt∝ M3p/h7 (gas capture within the planet's Bondi sphere) at lower planet masses and dMp/dt∝ Mp/h (gas capture within the planet's Hill sphere) at intermediate planet masses. At higher planet masses, the accretion rate reduces due to gap formation. (3) During the run-away mass growth phase, a planet migrates inwards by only about 20% in radius before achieving a mass on the order of Jupiter's. (4) For standard planet and disk conditions, we find no evidence of fast migration driven by coorbital torques (Type III migration). We do find evidence of Type III migration for a planet of fixed Saturn's mass, which is immersed in a cold (h~ 0.03) and massive (~ 0.02 M☉) disk, whose migration begins before gap formation completes. The migration can be explained with a model in which the torque is due to an asymmetry in density between trapped gas on the leading side of the planet and ambient gas on the trailing side of the planet.
P31A-1381
Evidence for a Tsunamigenic Impact Event in the New York Metropolitan Area Approximately 2300 B.P.
Oceanic impacts are a growing source of concern for the scientific community. Though the Earth is ~70 percent covered with water, and logic would therefore dictate that ~70 percent of impacts occur in the oceans, scientific investigations have focused on continental events. This is in part due to the difficulties inherent in examining submarine impact structures. Oceanic impacts lack many of the known features of continental events; however, oceanic impacts, unlike their continental counterparts, produce catastrophic tsunami events that may be used to identify them. Recent discoveries point to a tsunami event that affected the New York metropolitan area approximately 2300 years ago (Goodbred et al. 2006). Here it is shown that impact ejecta found in the tsunami deposit layer indicate an oceanic impact as the source of the tsunami. The sharp resolution of the stratigraphic study of the cores suggests that the sediment containing the impact ejecta was deposited in a tsunami-like event, rather than reworking from an older event. Samples were taken from the layer in sediment cores CD01-01, CD01-02, SD30, and VM32-2 from the Hudson River. Layer thickness ranged from approximately half a meter in CD01-02 to four centimeters in VM32-2. Individual ejecta grains were identified through an examination of the tsunami layer samples with optical and electron microscopy, as well compositional analysis via energy dispersive X-ray spectroscopy. Carbon and aluminum silicate impact spherules were found in the samples. Also present in the samples were shock-metamorphosed phases of feldspar, ilmenite, and olivine exhibiting planar deformation features and shock lamellae consistent with studies of known impact ejecta. TEM studies of the spherules revealed the presence of associated hexagonal nanodiamonds, also known as lonsdaleite, which are uniquely related to shock formation. In addition, the New York area lacks the extreme seismic and volcanic activity that might produce similar results, leaving a hypervelocity bolide impact as the most likely source for the tsunami event and associated impact ejecta. As oceanic impacts pose a serious threat to coastal communities around the world, it is necessary to understand both their frequency and effects. It is hoped that this method of identifying an oceanic impact via the ejecta found in tsunami deposits will improve our understanding of submarine impact events. Citations Goodbred, S., Krentz, S. LoCicero, P., Nitsche, F., Carbotte, S., and A. Slagle. Evidence for a newly discovered 2300-year-old tsunami deposit from Long Island, New York. Eos Trans. AGU 87(53), Fall Meet. Suppl., Abstract OS43C-0681
P31A-1382
Do The Concentrations Of Platinum Group Elements In The Younger Dryas Black Layer Really Support An Extraterrestrial Origin?
An enigmatic carbon-rich black layer, of possible worldwide occurrence, is interpreted to indicate an extraterrestrial impact around 12.9 ka, a period coeval with the Younger Dryas (YD) environmental changes (Firestone et al. 2007, PNAS 104). This interpretation is based on the possible identification of a series of markers postulated to be of impact origin, such as magnetic grains and microspherules, charcoal, soot, C- spherules, nanodiamonds, fullerenes with extraterrestrial He and elevated concentrations of Ir. Among these markers, only the elevated Ir concentration is a non-ambiguous impact indicator. In early 2007, one of us (PC) measured the concentration of platinum group elements (including Ir) in 4 samples of this black layer. Allen West provided the samples along with their Ir concentrations. The samples originated from Howard Bay, NC (level HB-11D2) and Blackwater Draw, NM (levels BW-DT, D/C and BW-B/A), and were supposed to contain 15 ng/g Ir (<150 micron magnetic fraction), 2.0 ng/g Ir (bulk sediment), 2.25 ng/g Ir (bulk sediment) and <0.1 ng/g Ir (bulk sediment) respectively. In Table 1 of Firestone et al. (2007) the Blackwater Draw sample contains 2.3 ng/g Ir, and the separated magnetic fraction rises up 24 ng/g. The obtained results showed that none of the 4 samples yielded PGE concentrations above 0.5 ng/g. Considering the attention the claim of a possible YD impact has generated in the last year, we are currently reanalyzing these 4 samples of the black layer using high precision NiS fire-assay preconcentration combined with ICP-MS analyses. On proven crater melt rocks or impact layers, the quantitation limits reach: 0.06 ng/g Ru, 0.01 ng/g Rh, 0.14 ng/g Pd, 0.06 ng/g Ir, and 0.1 ng/g Pt, far below the Ir values claimed by Firestone et al. (2007). In addition, these 4 samples are being analyzed for Os isotopes, known to be most sensitive for the detection of minute amounts of extraterrestrial components (%<%%<%0.05 wt%) in impact layers. The results of these new analyses will confirm or not the extraterrestrial origin of the Younger Dryas C-rich black layer.
P31A-1383
Pristine Samples of Silicon Carbide Separated From the Canyon Diablo Meteorite
The Canyon Diablo is an iron meteorite whose collision with Earth created Meteor Crater in Arizona. In a study of a large block (53 kg) of this meteorite, Henri Moissan reported his findings of green, hexagonal crystals of silicon carbide (SiC) which was given the name moissanite the following year by George Kunz (1905). Moissan did not report finding the cubic form of SiC. Subsequently, many erroneous reports appeared when the polishing compound (synthetic SiC) was mistakenly considered by researchers as a natural mineral associated with, rather than a contaminant of many rock types. Hence, the occurrence of SiC in the Canyon Diablo remains in doubt, and any proposal to investigate this problem was discouraged and regarded as predictably unproductive. This notion hampered further work on abundant materials housed in museums. SiC grains have been found in primitive meteorites and interplanetary dust particles. Some have been identified as presolar grains. The significance of SiC in the Canyon Diablo cannot be revealed unless we have abundant data from pristine samples, enough for us to classify them into presolar or other types. We report here a simple method we used to separate SiC crystals from the meteorite. We chose samples containing a carbon nodule composed of graphite, diamond-lonsdaleite, and SiC grains in the iron matrix. We broke up the carbon nodule with a sharp tungsten carbide chisel and hammer. After removing the large metal fragments, we put a small amount of the fine black grains in a Petri dish with acetone, then swerved the dish to scatter the grains sparingly on the bottom of the dish. Under a binocular microscope, SiC crystals can be spotted easily by their adamantine luster, color (blue, green, beige, etc.), and high birefringence when placed between crossed polarizers of a petrographic microscope. We also X-rayed individual grains, and have identified several hexagonal polytype structures as well as the cubic form (3C polytype).
P31A-1384
Re-evaluating the 38th Parallel Serial Impact Hypothesis
The idea that the 38th-parallel structures across Kansas, Missouri, and Illinois are serial impacts has been controversial. In addition to the original eight, two other structures are proximal to the 38th parallel, Dent Branch and Silver City Dome. Only Weaubleau, Decaturville, and Crooked Creek contain quartz grains with multiple directions of planar deformational features (PDFs). Shatter cones have been found at Decaturville and Crooked Creek. Key macroscopic observations of these impacts include: (1) circular outlines and notable central uplifts, (2) remarkably intense levels of structural deformation (folding, faulting, fracturing, and brecciation), (3) deformation dying out with depth and laterally away from the central uplift, and (4) associated igneous rocks only as clasts. From field and core studies and published reports, we consider other structures along the 38th parallel to be dubious (Hazelgreen), intrusive, (Hick's Dome), or volcanic in origin (Silver City Dome, Rose Dome, Furnace Creek, Dent Branch, and Avon). The age of the Weaubleau structure is constrained biostratigraphically as middle Mississippian (latest Osagean or early Meramecian). Crooked Creek and Decaturville are deeply eroded; their ages are poorly constrained. Crooked Creek contains isolated blocks of sandstone of late Osagean age, but the stratigraphic context of the blocks is poorly known. Other investigators contend the age of Decaturville is Pennsylvanian or Permian, based on CRM paleomagnetism and occurrence of an isolated sulfide breccia body in the central uplift. The Ozark plateau experienced Missouri Valley Type (MVT) sulfide mineralization during the Ouachita orogeny, but our examination of a sample from the sulfide breccia shows it is shattered pyrite and differs from typical MVT deposits. If the breccia is not associated with the regional mineralization, a middle Mississippian age cannot be excluded. Weaubleau, Decaturville, and Crooked Creek are aligned across 199 km. A line connecting the centers of the central uplifts of Weaubleau and Crooked Creek passes 1.5 km north of the center of Decaturville. Monte Carlo simulation was used to examine the probability that three temporally unrelated impacts could be aligned (±2° angular discordance) randomly over relatively short distances in an area that approximates the continental land surface. Modeling variables included number of impacts (N=200, N=300...N=1,000) and search radii (100-600 km). Twenty repetitions of 10,000 runs provided for analysis of standard deviation. For N=200 and radius of 100 km, an average of 6.6±2.5 aligned sets were found. For N=300, the results were 25.9±3.7, yielding a probability of P=0.003. Larger sample sizes and wider search radii produced more probable results, but given the number of known impacts (~175), it is highly improbable that Weaubleau, Decaturville, and Crooked Creek structures could be aligned but not temporally related. If Weaubleau, Decaturville, and Crooked Creek were products of a serial impact, they were not analogous with the Shoemaker-Levy 9 impacts on Jupiter, where planetary rotation affected the distribution, so the impacts would have occurred within seconds. In Mississippian paleogeographic reconstructions, the direction of impact would have been WSW-ENE, arguably along the ecliptic and near the equator. The distribution of deformation at Weaubleau suggests an oblique impact from present-day WSW-ENE, an argument against the serial impact hypothesis.
P31A-1385
Imaging Subsurface Crater Deformation using Controlled-Source Electromagnetics: Experimental Design Guidelines With Application to the Odessa TX Meteorite Impact Site
Crater formation by meteorites is a natural geologic process which has occurred throughout the history of our solar system. The crater morphology provides valuable insights into the prevailing geological conditions at the time of the meteorite impact, whether it occurred on Earth, Moon, Mars or other planetary body. Controlled-source electromagnetic geophysical methods provide a noninvasive means of characterizing subsurface structure. Our goal is to provide guidelines for imaging subsurface deformation and inferring the magnitude of the collision, in view of our primary target which is the shape of the deformation. We show that topography must be taken into account when analyzing the controlled-source electromagnetic response. The Texas A&M University (TAMU) finite element code is used to model these effects. Using the code we have run experimental design studies based on the Odessa TX impact crater, with its well-constrained subsurface deformation geometry, as a template. Different parameters are changed to determine the response of possible deformation scenarios. These parameters include the background conductivity, and the width and thickness of the deformation zone. Evaluating a suite of models enables us to determine optimal transmitter and receiver geometries. We have applied the experimental design procedure to study the shape and size of the subsurface deformation at the Odessa meteorite impact site.
P31A-1386
Simple Impact Crater Shapes From Shadows - The Sequel
At the last LPSC meeting I presented the outline of a method for determining simple impact crater shapes from shadows. In theory the shadow cast within a simple crater provides enough information to derive its cross-sectional shape from shadow measurements, at least to the maximum depth to which the shadow extends. Under certain simple assumptions, this can be done analytically. If the crater is conic-section - shaped, then it can be shown that the down-sun bound of any shadow cast within it is elliptical, with one axis along the direction of illumination and the other (perpendicular to it) of semi-length D/2 (where D is diameter). The properties of this shadow-ellipse can be related to the parameters of the crater shape conic-section, thus measurements of the shadow-ellipse yield not only crater depth and diameter but also the approximate crater shape, in terms of conic sections. The method also does not depend upon the shadow crossing near the crater center, which avoids a pitfall of older shadow measurement methods. The technique is also amenable to computer implementation, which has already been largely completed. Once computerized, crater measurements can be made rapidly and repeatably. The program reads in an image, its resolution, and the solar elevation and azimuth. The user then defines the crater rim by 'clicking' on three points, and the shadow ellipse by clicking on two more. The program calculates and outputs the diameter, the depth, and parameters describing the crater's approximating conic-section. It is highly applicable to situations where only single-image photography is available, for example MESSENGER flybys of Mercury. At the meeting I will present the finished math for this method and give some examples of its use.
P31A-1387
Technique for acceleration of projectiles to a velocity larger than the escape velocity of Earth 11.2 km/s
We accelerate glass and aluminium spheres with a size of 0.1 - 0.4 mm to a velocity higher than 10 km/s using a high-power laser, GEKKO XII - HIPER at Institute of Laser Engineering, Osaka University. Using an x- ray backlight system, in which we observe the projectiles in a shadow of intense x-ray, we can estimate the velocity of projectiles by a streak camera. Also, using this system, their shape can be observed by a framing camera. The projectiles are finally collided to LiF targets. It is expected that LiF does not vaporize with an impact velocity lower than 10 km/s. We observe some lines of Li when a glass projectile collide LiF at ~ 20 km/s, using a time-resolved spectrometer after an estimated impact time. This is the first observation of the impact vaporization with a higher velocity than 10 km/s.
P31A-1388
Dust Measurements Between Earth and Saturn by the Venetia Burney Student Dust Counter of the New Horizons Mission
The Venetia Burney Student Dust Counter (VSDC) on the New Horizons mission is a dust impact detector
designed to map the interplanetary dust distribution along the trajectory of the spacecraft as it traverses our
solar system. VSDC is the first student-built instrument on a deep space mission and is currently operated by
a small group of undergraduate and graduate students at the Laboratory for Atmospheric and Space
Physics (LASP), University of Colorado. VSDC is based on permanently polarized thin plastic film sensors
that generate an electrical signal when a dust particle impacts them. The total surface area is about 0.1
square meters and the detection threshold is about 1 micron in radius. By the time of this meeting (12/2008),
VSDC will have operated for about 500 days, and will have data covering an approximate distance of 1.2 to
11.0 AU from the Sun.
In this talk, we will briefly review the VSDC instrument, including the in-flight calibrations and tests. We will
report on the measured spatial and size distribution of interplanetary dust particles before and after the New
Horizons encounter with Jupiter. These data will also be compared to earlier measurements by Ulysses and
Galileo.
http://lasp.colorado.edu/sdc/