LPI Seminar Series


The LPI Seminar Series brings prominent scientists to the LPI to present on a broad array of scientific disciplines that advance our understanding of the solar system. The seminar series, which began in September 1969, has brought many notable contributors from numerous research and academic institutions to the LPI. Seminars are typically held on Thursdays from 3:00-4:00 p.m. CDT, but dates and times are subject to change. All seminars will be held virtually until further notice.

Sign up for LPI Seminars to receive email notifications of upcoming seminars and details on how to join the virtual seminar. For more information, please contact Patrick McGovern (McGovern@lpi.usra.edu) and Sean O’Hara (sohara@lpi.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.

View Recordings  

January 2013

Friday, January 11, 2013 - Lecture Hall, 3:30 PM
Paul Hayne, Caltech
Carbon Dioxide Snowfall and the Present Climate of Mars

In the perpetual darkness of Martian polar winter, temperatures drop so low that the air freezes out, forming the seasonal carbon dioxide ice caps. Under the grazing rays of polar summer, the caps replenish the atmosphere through sublimation. This seasonal exchange of carbon dioxide between the atmosphere and polar caps results in roughly 25% variations in atmospheric pressure and dramatically affects the atmospheric circulation. Energy balance in the polar regions drives the process, with the latent heat of CO2 deposition primarily offsetting the radiative energy loss to space during polar night. Most CO2 deposition probably occurs directly at the surface, but some accumulation may be due to CO2 snowfall. Cloud echoes by the Mars Orbiter Laser Altimeter (MOLA) and saturated atmospheric temperature profiles were tantalizing hints of this process. Using new data from the Mars Climate Sounder (MCS), I will show that CO2 snowfall is a common occurrence in both hemispheres and seems to be the dominant process controlling the thickness of the seasonal caps. The snowiest place in the south polar region is the south polar residual cap, which probably persists by maintaining a high albedo during summer. Intriguing similarities and differences between the hemispheres emerge, lending insight into the presence of the south polar residual cap and its role in buffering the present-day climate of Mars.

Friday, January 25, 2013 - Lecture Hall, 3:30 PM
Thomas Davison, University of Chicago
The Impact Histories of Meteorite Parent Bodies

Collisions between planetesimals during the early stages of planet formation were fundamental and frequent processes, and are often invoked to explain petrologic features of meteorites. To fully understand the collisional history of a meteorite parent body, and therefore draw conclusions about the conditions in the early Solar System, the number and type of impacts expected on a parent body must be quantified. In this talk, I will present our progress in developing a statistical framework to describe the the range of plausible collisional histories for individual meteorite parent bodies. Then, using this information, I will discuss the collateral effects of some collision scenarios that many parent bodies are likely to experience. We find that localized heating in collisions is common, and that the long term thermal effects of collisions can have significant implications for our understanding of the early Solar System.

February 2013

Friday, February 1, 2013 - Lecture Hall, 3:30 PM
Devin Schrader, University of Hawaii
The Role of Gas and Liquid in the Formation and Alteration of the Renazzo-like Carbonaceous Chondrites

The Renazzo-like carbonaceous (CR) chondrites are among the least altered samples from the early Solar System, and record conditions present within the protoplanetary disk during their formation. Via a petrographic and compositional study, I will discuss both the pre-accretionary formation conditions of their chondrules and post- accretionary parent asteroid processing. Chondrule formation, as recorded by chondrules in the CR chondrites, took place under conditions which were dust- and ice-rich relative to solar values. Gas-liquid oxidation/sulfidation of Fe,Ni metal is recorded in these chondrules; this corrosion occurred either during chondrule cooling, or during reheating events. After chondrule formation the CR chondrite parent asteroid accreted 16O-poor ice and experienced variable degrees of aqueous alteration, possibly due to heterogeneity in accreted ice or ammonia abundances and/or differing depth within the asteroid.

Friday, February 8, 2013 - Lecture Hall, 3:30 PM
Andrew Poppe, UC Berkeley
ARTEMIS Pick-Up Ions Observations of the Lunar Neutral Exosphere

The Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission is a dual-probe plasma and fields mission currently in orbit around the Moon. Among its many scientific objectives is to study pick-up ions at the Moon, with the goal of understanding various production mechanisms, such as photo-ionization, sputtering and charge exchange, and the subsequent behavior and impact on the lunar plasma environment. To this end, we have recently reported observations of lunar pick-up ions both in the solar wind and in the terrestrial magnetotail, which the Moon crosses for several days each month. A detailed study of these observations has revealed that these pick-up ions are affected by both the convection electric field and the lunar surface photoelectric field, which gives rise to complex pick-up ion distributions. I have constructed a particle-tracing model to explore the pick-up ion behavior and have used the model place constraints on the density and distribution of the lunar neutral exosphere. I will present the results of the data/model comparison and interpret these results in the context of various neutral exosphere production mechanisms operating at the Moon.

Tuesday, February 12, 2013 - Lecture Hall, 3:30 PM
Fred Singer, Chair, Science & Environmental Policy
Early Mars: Steps Towards Development of Life

Any investigation of development of life on early Mars is of necessity speculative; yet key steps, with assumptions clearly spelled out, can be profitably discussed. This paper focuses on the moons of Mars as the key to life development. The paper discusses (1) a novel hypothesis on the origin of Phobos and Deimos; (2) their possible role in the development of the Martian core; (3) development of Mars’ magnetic field; (4) history of oceans and atmosphere in the presence of a temporary magnetosphere; -- and finally, (5) some speculation about the possibility of different varieties of life forms originating at several independent locations on Mars.

April 2013

Friday, April 5, 2013 - Lecture Hall, 3:30 PM
Walter Kiefer, Lunar and Planetary Institute
GRAIL Explores the Moon's Interior

The overarching science goal for NASA’s GRAIL mission was to understand the structure of the Moon’s interior from crust to core. GRAIL mapped the Moon’s gravity field at elevations between 3 and 55 km during 2012. The resulting gravity map reveals features as small as 7 to 9 km across and is the best global gravity map for any planetary object, including Earth. When combined with recent measurements of the Moon’s global topography, GRAIL has dramatically improved our knowledge of the Moon’s internal structure. The bulk density of the lunar crust is about 10% lower than anticipated by prior geophysical models but is consistent with lab measurements of lunar rocks. The bulk density is particularly low surrounding major impact basins, reflecting the high porosity of basin ejecta sheets. The gravity observations require the presence of large volumes of intrusive basaltic material in the Aristarchus and Marius Hills volcanic fields, whereas the Cauchy and Hortensius volcanic fields do not contain such intrusions. Intrusive volcanism is also a likely contributor to the gravity anomalies at impact basin mascons, such as the Orientale basin.

Friday, April 12, 2013 - Lecture Hall, 3:30 PM
Doug Hemingway, University of California, Santa Cruz
Lunar Crustal Magnetism — Origins and Influence on Space Weathering

Although the Moon does not now possess a global magnetic field, its surface is dotted with strong crustal magnetic anomalies, often hundreds of kilometers across. These enigmatic magnetic features may be the signatures of a now extinct dynamo but could also be the result of exotic processes related to basin-forming impact events. In any case, the magnetic anomalies are important clues to the Moon's early history and evolution. Curiously, many of the magnetic anomalies are accompanied by complex, sinuous patterns of bright surface markings, known as "swirls". A strong candidate explanation for the appearance of swirls is that they form where locally strong magnetic fields disturb space weathering patterns, effectively shielding portions of the surface from the darkening effects of solar wind ion bombardment. In this talk, I will show that an analysis of the local magnetic field geometry supports the solar wind shielding hypothesis and I will discuss how the modeling results give insights into the underlying magnetic sources and the nature of the magnetizing field. I will also discuss the possibility of a low-cost spacecraft mission that could collect the extremely low altitude measurements needed to test our predictions.

Friday, April 26, 2013 - Lecture Hall, 3:30 PM
Andrew Dombard, University of Illinois at Chicago
The Great (and Perplexing) Equatorial Ridge on Saturn's Moon Iapetus

The equatorial ridge on Iapetus is one of the most peculiar features in the solar system. A mountain range up to 20 km high, it runs perfectly along the moon's equator for most of its circumference. The formation of this ridge has baffled scientists since its discovery almost a decade ago. Here, I review models that have been proposed to explain the ridge and argue that it is the end product of a sub-satellite formed by a giant impact during the formation of the solar system.

May 2013

Friday, May 3, 2013 - Lecture Hall, 3:30 PM
Veronica Bray, University of Arizona
CRISM Analysis of Crater Uplifts

The central uplifts of large impact craters can expose bedrock and ancient crust that are otherwise buried. One example is the central peak of the 79 km diameter Ritchey crater (28.8°S, 309°E). Ritchey Crater is near the boundary between Hesperian ridged plains and Noachian highland terrain units on the global geologic map of Mars. We are conducting lithological mapping of the central uplifts of Ritchey and other craters in order to reconstruct the stratigraphy of buried noachian crust in the region between Corprates Chasma and the Argyre basin.

Friday, May 31, 2013 - Lecture Hall, 3:30 PM
Tom Zega, University of Arizona
Decoding the High-Temperature Origins of Refractory Oxides from Ancient Stars

As stars evolve, they shed their matter through dust-driven stellar winds or explosive events such as supernovae. These stellar ashes can enter the interstellar medium and become the starting material for a new star. Our own solar system formed partly from the remnants of ancient stars, and it was long ago suspected that individual grains of this presolar stardust material should have survived intact within the solid relics leftover from its birth, i.e., primitive meteorites. The isolation and measurement of presolar grains has been a decades-long struggle, largely because many of them occur intimately mixed at the nanometer scale in chondritic meteorites - the bulk of which contain phases that formed in our own solar system. In recent years, developments in electron and ion optics have revolutionized our ability to measure the isotopic composition of a grain, extract it in situ, and investigate its crystal chemistry and structure. Such information is fundamental to inferring the origins of such grains, e.g., the type, mass, and composition of their parent stars as well as the thermodynamic processes of their circumstellar envelopes and secondary processing they experienced within our solar system. I will show how secondary ion mass spectrometry, focused-ion-beam scanning-electron-microscopy, and transmission electron microscopy (TEM) can be combined to gain insight into the origin of presolar spinel (MgAl2O4) and hibonite (CaAl12O19) grains.

June 2013

Friday, June 7, 2013 - Lecture Hall, 3:30 PM
Shoshana Weider
The Surface Composition of Mercury From MESSENGER Data

Geochemical results from the X-Ray and Gamma-Ray Spectrometers onboard the MESSENGER spacecraft, and insights they provide into Mercury's formation and geological evolution Shoshana Weider

Friday, June 14, 2013 - Lecture Hall, 3:30 PM
Kelsi Singer, Washington University, St. Louis
Massive Ice Avalanches on Iapetus Mobilized by Friction Reduction During Flash Heating

Large ice avalanches on saturnian satellites exhibit a behavior similar to long-runout landslides found across the solar system: some mechanism (or mechanisms) apparently reduces the material’s friction, allowing the landslides to travel 10-30 times their drop heights (as opposed to ~2x for a more “normal” frictional regime). These landslides achieve immense runout lengths, even over variable slopes and topography. Landslides on Iapetus are some of the longest and most voluminous in the solar system, reaching lengths of 80 km. I will compare the long-runout landslides on icy satellites to their rocky cousins found on Earth and Mars, and discuss a possible friction reduction mechanism through flash heating.

Friday, June 21, 2013 - Lecture Hall, 3:30 PM
Francis McCubbin, University of New Mexico
Magmatic Volatiles in the Inner Solar System: Constraints from Apatite in Planetary Materials and Apatite-Melt Partitioning Experiments TBD

Magmatic volatiles like water, C-species, S- species, N-species, and the halides play many important roles in geologic processes on Earth, from magma genesis to climate change. Furthermore, these components are the basis of organic chemistry and they are required for life. However, little is known about the origin, abundances, and roles of magmatic volatiles among the other terrestrial bodies in our Solar System. In the present study, we attempt to gain a first-order understanding of the magmatic volatiles H2O, F, and Cl through analyses and experimental work centered around the calcium-phosphate mineral apatite. The mineral apatite contains F, Cl, and OH as essential structural constituents, and it is ubiquitous in planetary materials. Consequently, we have analyzed apatites from Earth, Moon, Mars, 4-Vesta, and ordinary chondrites to gain a better understanding of the magmatic volatile inventories and distributions within those bodies. Importantly, apatite does not mirror the magmatic volatile load of a fluid or melt from which it formed; therefore, we have conducted petrologic experiments to investigate the partitioning behavior of H2O, F, and Cl between apatite and silicate melts. These experiments allow one to develop quantitative models to to infer concentrations of volatiles in magmatic liquids and source regions. Our work has shown that the inner Solar System is looking much wetter than it has in the past, raising important questions about the origin of volatiles in the terrestrial planets.

Friday, June 28, 2013 - Lecture Hall, 3:30 PM
Rosalind Armytage, University of Houston
The Si isotopic Composition of Meteorites and Lunar Rocks –Insights into Building the Earth and Moon

Silicon is a major element in most of the rock-forming phases, and recent developments in mass spectrometry techniques, in particular MC-ICP-MS, make Si isotopes an attractive tool to understand events during the earliest stages of formation of terrestrial planets. High precision Si isotopic measurements on meteorites and lunar rocks can provide important constraints on the light element in the Earth’s core and the formation of the Moon.

July 2013

Friday, July 26, 2013 - Lecture Hall, 3:30 PM
Oliver White, Lunar and Planetary Institute
Crater Relaxation on the Saturnian Mid-Sized Icy Satellites and its Relation to their Thermal Histories

Evidence for relaxation of impact crater topography has been observed on many icy satellites, including those of Saturn, and the magnitude of relaxation can be related to past heat flow. Earlier surveys of crater morphologies using shadow lengths and photoclinometry (shape-from-shading) processing of Voyager imagery have yielded depth/diameter measurements for only a limited number of craters across a fairly narrow size range. We have used new stereo- and photoclinometry-derived global digital elevation models (DEMs) of the surfaces of these satellites that we have generated from Cassini data to obtain measurements for many more craters across a much wider size range than was previously possible. For the satellites Rhea, Iapetus and Dione, we have obtained enough measurements to define a scale of relaxation for the craters. We have performed relaxation simulations to determine what heat flow magnitudes and durations are necessary in order to achieve the current morphologies of certain relaxed and unrelaxed craters. When combined with age estimates based on crater counting, these results contain strong implications for the thermal histories and heating mechanisms of these satellites, and aid in constraining models for their origins.

August 2013

Friday, August 23, 2013 - Lecture Hall, 3:30 PM
Michael Poston, Georgia Tech
A Chemist’s Perspective on Modern Lunar Water from Laboratory Experiments and Modeling

Recent, unexpected detections of infrared absorptions consistent with hydroxyl and possibly water (Clark 2009, Pieters et al 2009, Sunshine et al 2009) on the sunlit lunar surface provoke questions about the origins and retention mechanisms of volatile species in the harsh lunar environment. Additionally, hints of significant diurnal variation in hydroxyl/water content by IR spectroscopy (Sunshine et al 2009) and neutron depletion (Livengood et al 2012) remote sensing support the likelihood of a dynamic cycle of hydroxyl/water loss, migration, and replenishment each lunar day. Monte Carlo models (e.g. Crider and Vondrak 2000) show that a significant portion of any migrating water will likely end up sequestered in permanently shadowed regions (PSRs) at the lunar poles. However, an array of remote detection techniques has shown evidence for only small amounts of water-ice in some PSRs, and little or no evidence for water-ice in others. What is the source of this apparent discrepancy? Experiments and modeling in the Orlando research group are underway to provide critical details to improve our understanding of both thermal and non-thermal processes occurring at the surfaces of lunar grains. This seminar will discuss: 1) laboratory experiments measuring the desorption activation energy of water molecules from lunar surrogates and returned Apollo soils, 2) computer modeling of the chemical and physical processes expected to occur when the solar wind interacts with lunar grains, and 3) laboratory experiments measuring the photon-induced loss mechanisms of thin layers of solid water on lunar rock surfaces. The results of these examinations will be related back to recent lunar observations and the possible implications for modern lunar water. ------------ Michael J. Poston1, A. B. Aleksandrov1, G. A. Grieves1, A. J. DeSimon1, C. A. Hibbitts2, M. D. Dyar3, T. M. Orlando1, 1School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA, 30332, michael.poston@gatech.edu. 2Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723. 3Mount Holyoke College, Dept. of Astronomy, South Hadley, MA, 01075.

Wednesday, August 28, 2013 - Lecture Hall, 3:30 AM
Paul Byrne
Mercury: Global Tectonics on a Contracting Planet

The surface of Mercury is replete with tectonic landforms interpreted to be products of horizontal shortening that accompanied planetary cooling and contraction, but the number and distribution of such structures and their relation to large-scale variations in topography have not been well understood. Additionally, prior estimates of the amount of global contraction from photogeological studies of shortening structures were far less than predicted by interior thermal history models. In this talk I present a global synthesis of deformational structures on Mercury derived from orbital imaging and topographic measurements by the MESSENGER spacecraft. Lithospheric shortening on Mercury has been accommodated by a substantially greater number and variety of landforms than previously recognized, including by long fold-and-thrust belts as on Earth. These new observations show that Mercury contracted radially by as much as 7 km, well in excess of the 0.8–3 km previously reported from photogeology. This new measure of Mercury's planetary radius change provides a critical constraint for future studies of the planet's thermal history, bulk silicate abundances of heat-producing elements, mantle convection, and the structure of its large metallic core, and our observations offer fresh insight for investigating the Mercury's tectonic and volcanic development.

September 2013

Friday, September 6, 2013 - Lecture Hall, 3:30 PM
Justin Filiberto, Southern Illinois University
Conditions of Basalt Genesis in Mars from Basalts in Gusev Crater and Meridiani Planum, Compared with the Martian Meteorites

Until recently, the SNC meteorites represented the only source of information about martian igneous chemistry. This changed with the Mars Exploration Rovers and Mars Science Laboratory, which have analyzed basalts on the surface of Mars in Gusev Crater, Meridiani Planum, and Gale Crater. Compared to the Martian meteorite basalts, the analyzed surface basalts are thought to be much older (~3.65 vs. 1.0-0.17 Ga) and have distinctly different chemistries. Because of the differences in basalt chemistry, we can constrain how the Martian mantle may have changed through time

Friday, September 13, 2013 - Lecture Hall, 3:30 PM
James Dickson, Brown University
Time-Lapse Photography of the McMurdo Dry Valleys, Antarctica: What the Coldest and Driest Place on Earth tells us about the Potential for Liquid Water on the Surface of Present-Day Mars.

This talk will give an overview of our current understanding of the role of ice and liquid water on and near the surface of Mars in its most recent history. This will provide the context for a discussion of fluvial processes in the McMurdo Dry Valleys of Antarctica, the coldest and driest terrain on Earth where water can still flow across the surface and support ecosystems. Long-duration, high-frequency, high-resolution time-lapse photography, synchronized with meteorological measurements, allows us to determine how small changes in atmospheric conditions result in significant changes in surface albedo and morphology that are observable from orbit. When Antarctica and Late Amazonian Mars are viewed together, it appears that the regions of contemporary Mars most conducive to liquid water and the regions of Earth least conducive to liquid water behave in much the same way.

Wednesday, September 18, 2013 - Lecture Hall, 3:30 PM
Tanya Peretyazhko, Rice University
Reduction of Fe(III) (hydr)oxides: Mechanisms and Environmental Impact

Iron (Fe), one of the most common elements on Earth, is frequently found in Fe(III) and Fe(II) oxidation states. Reduction from Fe(III) to Fe(II) has key impact on fate of various contaminants. In soils, sediments and subsurface materials Fe mainly exists in the oxidized form as insoluble Fe(III) (hydr)oxides but under anoxic conditions the reduced Fe(II) is present. The reduction of Fe(III) (hydr)oxides in the near-surface environment in driven by the activity of iron-reducing bacteria. These bacteria can reduce Fe(III) either by direct contact with the oxide surface or by indirect mechanisms not involving contacts. Depending on the conditions ferrous iron, Fe(II), produced by microbial reduction of Fe(III) is present in various forms including dissolved, adsorbed and secondary Fe(II) phases (e.g., vivianite, siderite, magnetite, green rust). Ferrous iron has been shown to provide an effective means for remediation a variety of pollutants including nitrite, nitrate, chromium, selenite, uranium, vanadate, pertechnetate, mercury and nitrobenzene from aqueous solution. In this presentation I’ll discuss mechanisms of microbial indirect reduction of Fe(III) (hydr)oxides. Our studies revealed production of Fe(II) that formed vivianite of complex morphology. I’ll further discuss the role that adsorbed and structural Fe(II) plays in reduction of contaminants such as pertechnetate and mercury.

Friday, September 20, 2013 - Lecture Hall, 3:30 PM
Heath Mills, UHCL
Hunting Intraterrestrials in the Deep Subsurface: Earth’s Last Great Biosphere Frontier

Life on planet Earth was viewed very differently during the days of the Apollo missions. As the mission’s namesake would suggest, life was thought to be linked to the sun. However, shortly after the sun set on the Apollo program, this binding connection between life and light was shattered. Researchers aboard a deep-sea submersible in the late 1970’s rewrote our understanding of life on Earth by exposing vast amounts of biological diversity at the bottom of the cold, dark ocean. As many researchers aim to continue looking outward for life, a community of intraterrestrial explorers focus inward, to examine the limits of life in the deep ocean and the marine subsurface. These environments can be as alien as many of the environments being considered for astrobiological analysis. Over the last decade, descriptions of the subseafloor microbial biosphere suggest that it is one of the largest biomes on the planet in spite of low concentrations of carbon and energy, reduced fluid flow, and isolation on the order geologic time-scales. My lab group has been able to identify not only the presence of microbial populations within the subsurface, but also metabolically active lineages capable of altering the surrounding strata and porewater chemistry. Recent efforts have extended our search beyond sediments to crustal materials. Characterizations of active populations within different forms of basalt represent a significant advancement in our understanding of the subsurface biosphere as previous estimates of biomass were limited to sediments alone. In addition, we have been able to isolate and characterize fungal populations from some of the most energy-limited environments on Earth and thus expanding subsurface diversity into the third domain of life. Moving forward, I would like to explore the opportunities to use our tools and techniques developed for nucleic acid-based characterizations of subsurface populations to build collaborations at JSC to foster new understandings of both life on Earth and the potential for life elsewhere. It is our belief that exploration of the deep marine subsurface can unlock many answers about the habitability of Earth while providing clues to possibility for life elsewhere.

Wednesday, September 25, 2013 - Lecture Hall, 3:30 PM
David Page, Oxford University
Geological Impact Crater Chronology

Impact crater chronology is a dating technique unique in geochronology – that surfaces can be dated visually is a powerful tool, quite unlike anything in terrestrial geology (try dating a random, unfossiliferous geological formation on Earth by visual means, and see how far you get!). Yet this chronology usually lacks stratigraphical constraint (in both horizontal and vertical dimensions), and can be more an exercise in physics than the geology of the surfaces that it seeks to date. Stratigraphically-controlled impact crater counts reveal that there is a great deal more information to be had from this chronology when we look with geological eyes, no more so than when dealing with the volatile-rich surfaces that are the focus of much contemporary planetary scientific inquiry.

Friday, September 27, 2013 - Hess Room, 3:30 PM
J.R. Skok, Louisiana State University
Probing the Pre-Noachian of Mars

On a geologically active, single plate planet like Mars, the earliest crust would be well preserved at depth but obscured by later processes. Impact craters provide one of the few, and only globally significant, windows into this deep crust. High-resolution spectral analysis of crater central peaks allows an investigation into the composition of this ancient crust and a way to test and refine models for planetary formation and crustal evolution. Spectral investigation suggests an ancient crust dominated by highly differentiated olivine and pyroxene cumulates. We consider this result in context with previous understanding of planetary formation and the probability of an early mantle overturn. This ancient cumulate crust would have important implications for early planetary habitability and the surface environment.

October 2013

Friday, October 18, 2013 - Lecture Hall, 3:30 PM
Francis Nimmo, University of California, Santa Cruz
Looking inside moons using gravity, topography and tides

The satellites of the outer solar system show great present-day diversity and have experienced wildly different histories. How did these differences arise? In this talk I will use spacecraft observations of gravity, topography and tides to investigate the cases of Enceladus and Titan, moons of Saturn with very different characteristics.

Wednesday, October 30, 2013 - Lecture Hall, 10:00 AM
Radwan Tajeddine, IMCCE-Paris Observatory
Mimas: Strong forced longitudinal librations and constraints to its internal structure with Cassini ISS observations.

The origin and the evolution of Saturn's satellites are being debated. For a long time, it has been thought that they were formed in Saturn's sub-nebula 4.5 billion years ago, when another model has recently appeared, forming the small and mid sized moons in the rings. At the same moment, another result concerning Saturn's dissipation factor Q appeared implying a fast expansion of the moons, except for Mimas, which is having a secular acceleration, starting a new debate about the Saturn's system dynamics. We used Cassini ISS NAC images to constrain, by photogrammetry, Mimas’ internal structure and origin. A topographic map of 260 surface chosen points has been built. A photogrammetric reconstruction method has been applied using colinearity equations to compute 3-D positions of control points, with a mean uncertainty of about 580 metres. A tri-axial shape of Mimas was built with these points, confirming that this satellite is not in the state of hydrostatic equilibrium. The control point network was also used to measure indirectly the amplitudes of the longitudinal physical librations of Mimas, confirming all the computed theoretical values, except the internal structure depending one, which almost doubles the theoretically predicted amplitude, resulting in a value of (B-A)/C = 0.091. A further analysis shows that Mimas' core was formed in the rings near the Roche limit and moved away keeping its initial shape until today causing the observed strong libration amplitude.

November 2013

Friday, November 15, 2013 - Lecture Hall, 3:30 PM
Britney Schmidt, Georgia Tech
Getting Under Europa’s Skin

Europa is one of the most enticing targets in the search for life beyond Earth,. With an icy outer shell hiding a global ocean, Europa exists in a dynamic environment, where immense tides from Jupiter potentially power an active deeper interior. Intense irradiation and impacts bathe the top of the ice shell. These processes are sources of energy that could sustain a biosphere. Why is all of this important? It’s simple: the search for extant life is more complicated than the search for water or an oxygen atmosphere. Earth’s biosphere is strongly coupled to activity—plate tectonics, weathering, glaciation; geologic processes are crucial to this living planet. In the past few decades the debate about habitability of Europa has been focused strongly on the thickness of its ice shell. However an arguably more critical question is: how does the ice shell really work? Galileo data indicated that Europa has undergone recent resurfacing, and implied that near-surface water was likely involved. New analysis of Europa's enigmatic "chaos terrains" indicates that chaos features may be actively forming today in the presence of a great deal of liquid water--above large liquid water bodies within 3km of Europa's surface. The detection of shallow subsurface "lakes" implies that rapid ice shell recycling could create a conveyor belt between the ice and ocean. Exchange between Europa's surface and subsurface could allow ocean material to one day be detected by spacecraft and will be mediated by melting, accretion, and redistribution at the base of the ice shell, processes not well understood even on Earth. And while microbial life within ice and below glaciers has been studied for decades, one of the most relevant terrestrial analog environments, the ice-ocean interface beneath ice shelves, has remained largely uncharacterized…until now. In this presentation, we will explore environments on Europa and their analogs on Earth. While we wait for the opportunity to send a new mission to Europa, looking to our own cosmic backyard, Antarctica, allows us to better understand Europa’s habitability and to develop techniques to explore this ice covered world not so unlike our own.

Friday, November 22, 2013 - Lecture Hall, 3:30 PM
Alberto E. Saal, Brown University
Hydrogen Isotopes in Lunar Volcanic Glasses implications of their Terrestrial heritage.

Since the Apollo mission 1969-1972 until 2008 the Moon was believed to be bone dry, consistent with the model for its formation by a giant impact ~ 4.5 billion years ago. All the Hydrogen was believed to be lost from the molten material that finally accreted to form the Moon. Since 2008 there has been clear evidences for the presence of H (most likely as OH-) in the lunar interior. Using the volatile contents and Hydrogen isotopes in lunar lavas, and comparing them with those of melts from Earth's upper mantle, we concluded that inside the Moon there are reservoirs with equivalent amount of H to the Earth's depleted upper mantle, and the H of the Moon-Earth system originated from primitive meteorites (chondrites), rather than comets. The simplest explanation is that the H was in Earth at the time of the giant impact and it was not significantly lost during the formation of the Moon; the H arrived very early during the main stages of accretion of the Terrestrial planets (consistent with dynamic models of planetary formation). Our data suggest that the H budget and isotopic composition for Earth did not change much since the formation of the Moon.

December 2013

Wednesday, December 4, 2013 - Lecture Hall, 3:30 PM
Jangmi Han, University of New Mexico
Microstructural Constraints on Complex Thermal Histories of Refractory Inclusions from CO3 Chondrites: A FIB/TEM Study.

I will present new micro to nano-scale textural and mineralogical observations obtained using a variety of microbeam techniques (field emission scanning electron microscope, electron microprobe, and focused ion beam/transmission electron microscope) from refractory inclusions (calcium-aluminum-rich inclusions and amoeboid olivine aggregates) in CO3 chondrites. The microstructural observations from ALH A77307 CO3.0 chondrite provide additional constraints on the formational and subsequent thermal histories of refractory inclusions in the context of the early solar nebula. In addition, new SEM and TEM observations from Kainsaz CO3.2 chondrite have the potential to develop a more comprehensive understanding of metamorphic and metasomatic effects on refractory inclusions on the parent body

Previous Seminars

2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | 2009 | 2008 | 2007 | 2006 | 2005 | 2004 | 2003 | 2002 | 2001 | 2000 | 1999 | 1998

Sign up for LPI Seminars

Sign up for LPI's email newsletters