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Lunar and Planetary Institute

LPI Seminar Series

2017

LPI seminars will be held on Thursdays.

LPI seminars are held from 3:30–4:30 p.m. in the Lecture Hall at USRA, 3600 Bay Area Boulevard, Houston, Texas. Refreshments are served at 4:30 p.m. For more information, please contact Martin Schmieder (phone: 281-486-2116; e-mail: schmieder@lpi.usra.edu) or Nick Castle (phone: 281-486-2144; e-mail: castle@lpi.usra.edu.) A map of the Clear Lake area is available here. This schedule is subject to revision.

Join the LPI-Seminars mailing list to receive email notifications about upcoming LPI Seminars. To join the mailing list please send an email to:
lpi-seminars-join@lists.hou.usra.edu.

See also the Rice University Department of Physics and Astronomy Colloquia and the Department of Earth Science Colloquia pages for other space science talks in the Houston area.

February 2017

Thursday, February 16, 2017 - Lecture Hall, 3:30 PM

Qiang Zhu, University of Nevada, Las Vegas
Evolutionary Crystal Structure Prediction: From Complex Crystals to Materials Defects
Knowing the atomic structure of a material or mineral offers a deeper understanding of its macroscopic physical phenomenons and its connection to our planet's architecture, composition and evolution. There have been tremendous progresses in the accurate prediction of crystal structures from first principles based on a variety of global optimization methods combing quantum mechanical calculations. In this talk, I will review the structure prediction methods based on evolutionary algorithms developed in my group, and its applications to study the minerals and organic crystal polymorphism at ordinary and extreme conditions. Furthermore, I will discuss its recent extension to study the highly complex interface in different solids. The encouraging results so far suggest a major role of this approach in studying the general phenomenon in materials and mineral sciences.

March 2017

Thursday, March 2, 2017 - Lecture Hall, 3:30 PM

David Patrick O'Brien, Planetary Science Institute
The Formation and Evolution of the Inner Solar System
In the "classical" model of terrestrial planet formation, planetesimals and planetary embryos accrete together to form the planets, with Jupiter and the other giant planets undergoing minimal migration during that time. The asteroid belt is an excited and depleted remnant of the material originally lying interior to Jupiter. This model can broadly reproduce many of the characteristics of the inner Solar System, but faces difficulties in matching some key details, in particular the small size of Mars compared to Earth and Venus. In the newer "Grand Tack" scenario, the giant planets undergo substantial radial migration during the early stages of terrestrial planet formation. This scenario provides a better match to the small size of Mars, and populates the asteroid belt with material scattered from much wider range of distances from the Sun. I will discuss these models in detail, in particular focusing on the implications for the delivery of water and other materials to the terrestrial planets, and the implications for the taxonomic distribution of asteroids and the collisional/dynamical histories recorded in the meteorite record.

June 2017

Friday, June 23, 2017 - Lecture Hall, 3:30 PM

Ellen Crapster-Pregont, Columbia University
LPI Seminar: Constraining the Chemical Environment and Processes in the Protoplanetary Disk: From the Perspective of Rare Earth Elements in CO Chondrites and Metal-rich Chondrules in CR Chondrites
Carbonaceous chondrites have an approximately solar bulk composition, with some exceptions (e.g. H), and exhibit a range of parent body alteration. Investigations of both pristine and altered chondrites yield valuable insight into the processes and conditions of the early Solar System prior to and resulting in the planets we observe today. Such insight and the dynamic models developed by astrophysicists are constrained by chemical, mineralogical, and textural characteristics of chondrite components (chondrules, refractory inclusions, metal, and matrix). This work explores two different types of datasets, rare earth element (REE) abundances of chondrite components and crystal orientation of metal in chondrules, to investigate the highest temperature processes in the early Solar System and the formation of chondrules, respectively. Colony CO3.0 and Moss CO3.6 were analyzed for REE abundances to determine the distribution of these elements among chondrite components. While refractory inclusions exhibit the greatest enrichments in REE relative to CI, after modal recombination chondrule glass contributes most significantly to the bulk REE budget in both chondrites. The bulk mean REE patterns for both Colony and Moss are flat and approximately CI in abundance while the mean REE patterns for components are nearly flat with relative enrichments (~10x CI for both chondrule glass and refractory inclusions) or depletions (chondrule olivine) relative to CI. Lack of correlations between REE and other characteristics, nearly flat REE patterns and nearly equivalent enrichment factors relative to CI across chondrite groups, including the CO chondrites analyzed here, implies that REE could have been equilibrated in precursor material prior to chondrite component formation. We propose a scenario for the equilibration of REE with vapor-solid or solid-solid reactions with subsequent accretion of chondrite components. Metal-rich chondrules in Acfer 139 (CR2) were used to investigate whether chemical and crystal orientation characteristics of the metal can add constraints to chondrule formation and deformation. Eight chondrules with abundant metal nodules, both as rims and within the chondrule interior, were analyzed in detail using EMP and EBSD techniques. One chondrule, chondrule A, is of particular interest as it contains three concentric metal layers. A combination of chemical inhomogeneity, multiple sets of twins, and other evidence of strain imply that the formation of these chondrules was not straightforward and involved multiple iterations of heating, and potentially addition of material. A plausible model of chondrule formation in the early Solar System must be able to account for this more complicated thermal and alteration history and produce the chemical and textural variety of chondrules present in the region of chondrite accretion.

July 2017

Thursday, July 13, 2017 - Lecture Hall, 3:30 PM

James A. Slavin, Department of Climate and Space Science & Engineering, University of Michigan
LPI Seminar: MESSENGER Observations of Mercury’s Dynamic Magnetosphere
Mercury’s magnetosphere is formed by the interaction of the solar wind with its small, ~ 200 nT – RM3, intrinsic magnetic field. The mean altitude of the subsolar magnetopause is only ~ 0.5 RM, but planetary induction currents in Mercury’s highly conducting iron core strongly resist solar wind compression. The weak conductivity of Mercury’s regolith severely limits field-aligned current intensity, but Region 1 currents are measured at low altitudes with magnitudes up to several tens of kilo-Amperes. These currents pass radially through Mercury’s ~ 400 km thick regolith to close across its iron core. Mercury’s surface-bounded exosphere is maintained by sputtering and other surface interactions that eject neutrals from the regolith. While the magnetospheric plasma is primarily of solar wind origin, i.e. H+ and He++, Na+ and other heavy planetary ions derived from the exosphere account for ~ 1 to 10% of ion number density. Magnetic reconnection at the magnetopause is far more frequent and intense than at Earth. “Showers” of 100+ flux transfer events are often observed during a single magnetopause traversal. Indeed, the dayside magnetosphere is sometimes observed to disappear during periods of strong southward interplanetary magnetic fields. Magnetic field loading/unloading of the magnetotail is observed at Mercury similar to that seen at Earth during substorms. Mercury’s substorms are associated with magnetic field dipolarization, energetic electron acceleration and plasmoid ejection, but they last only ~ 2 – 3 min as compared with ~ 1 – 2 hrs for Earth. Future prospects for understanding Mercury’s coupled magnetosphere – exosphere – solid planet as a system with the measurements to be returned by ESA’s BepiColombo mission in 2025 will be discussed.

August 2017

Thursday, August 24, 2017 - Lecture Hall, 3:30 PM

Tabb Christopher Prissel, Rutgers University
LPI Seminar: Application of Al-in-Olivine "Astrothermometry" to Extraterrestrial Igneous Systems
Volcanic and plutonic samples are directly linked to the constitution of planetary interiors. Further, igneous materials can preserve the thermal history of large-scale magmatic evolution including primary mantle accumulation, convective styles, hybridization, and source melting. We propose the first application of Al-in-olivine "astrothermometry" to understand the origin of key geochemical signatures observed among martian, lunar, and igneous astromaterials and their relationship to interior sources. In so doing, this work aims to establish chemical connections between the primary mantles of rocky bodies in order to redefine models of planetary differentiation.

September 2017

Thursday, September 28, 2017 - Lecture Hall, 3:30 PM

Kat Volk, University of Arizona
LPI Seminar: The curiously warped mean plane of the Kuiper belt
The mean orbital plane of a population of small bodies is set by the mass distribution in the solar system. We used the current set of observed Kuiper belt objects to measure the mean plane of this population as a function of semi-major axis. For the classical Kuiper belt as a whole (the non-resonant objects in the semi-major axis range 42-48 au), we find a mean plane that is in accord with theoretical expectations of the secular effects of the known planets. We detect a statistically significant warp in the mean plane near semi-major axes 40-42 au, where linear secular theory predicts a warp due to the nu_18 nodal secular resonance. For the more distant Kuiper belt objects of semi-major axes in the range 50-80 au, the expected mean plane is close to the invariable plane of the solar system. However, the measured mean plane deviates greatly from this expectation and is inclined roughly 7 degrees from the invariable plane. We estimate this deviation from the expected mean plane to be statistically significant at the 97-99% confidence level. There are several possible explanations for this deviation, including the possibility that a relatively close-in (a < 100 au), unseen small planetary-mass object in the outer solar system is responsible for the warping.

October 2017

Friday, October 6, 2017 - Lecture Hall, 3:30 PM

William Moore, Hampton University
LPI Seminar: Heat Pipe Planets
A look at the surfaces of the terrestrial planets other than Earth reveals vast plains of extruded lava, of mafic or even ultra-mafic composition, flowing over vast distances at low slopes from sources which are not elevated or even identifiable. On these bodies, tectonic deformation is dominated by compression, and ancient topographic and gravity anomalies have been preserved to the present without significant relaxation. Is there a single explanation for these shared features? The operation of volcanic heat pipes as the dominant heat transport mechanism in the early histories of these bodies may explain these observations and provide a universal model of the way terrestrial bodies transition from a magma-ocean state into subsequent single-plate, stagnant-lid convection or plate tectonic phases. In the heat-pipe cooling mode, magma moves from a high melt-fraction asthenosphere through the lithosphere to erupt and cool at the surface via narrow channels. Despite high surface heat flow, the rapid volcanic resurfacing produces a thick, cold, and strong lithosphere which undergoes contractional strain forced by downward advection of the surface toward smaller radii. In the absence of plate tectonics, heat-pipe cooling is the last significant endogenic resurfacing process experienced by most terrestrial bodies in the solar system, because subsequent stagnant-lid convection produces only weak tectonic deformation. Due to their higher heat content, terrestrial exoplanets appreciably larger than Earth may remain in heat-pipe mode for much of the lifespan of a Sun-like star and would likely be found in this stage of evolution — the stage in which life first arose on Earth.

 

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