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. US/Central, 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 Sam Crossley (email@example.com).
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.
Friday, January 8, 2016 - Lecture Hall, 3:30 PM
Matthew Weller, Rice University
Evolving Worlds: A Story of Planetary Evolution and Bi-Stability
Growing geodynamic and geochemical evidence suggests that plate tectonics may not have operated on the early Earth, with both the timing of its onset and the length of its activity far from certain. This work uses coupled 3D mantle convection and planetary tectonics simulations to explore evolutionary paths and planetary tectonic regimes. Early in the geologic lifetime of a terrestrial planet, high mantle temperatures favour stagnant-lids. As radiogenics decay, an initial stagnant-lid may yield into a high temperature mobile-lid state. The transition from an initial stagnant-lid is a function of yield strength, in addition to both internal and surface temperatures. For intermediate values of internal temperature, multiple stable tectonic states can exist. In these regions of parameter space, the specific evolutionary path of the system has a significant role in determining its tectonic state. This indicates that multiple modes of convection and surface tectonics can potentially operate on a single planetary body at different times in its evolution, as consequence of changing internal parameters, surface temperatures, and differing thermal histories. The implications of terrestrial worlds that can alternate, and be offset between multiple tectonic states over giga-year timescales will be discussed.
Friday, February 5, 2016 - Lecture Hall, 3:30 PM
Rhiannon Mayne, Texas Christian University
The History of Qarabawi's Camel Charm: A Meteoritic Artifact
Meteoritics, the study of meteorites, is usually focused on the scientific value of a sample; for example, what can it tell us about the formation of our Solar System, the planets, how Earth formed? It is rare for the cultural value of meteorites to be the focus, although there are a few examples. The Camel Charm is a meteoritic artifact acquired by the National Meteorite Collection at the Smithsonian’s National Museum of Natural History in 1974. It has never been studied. The Charm is made from an iron meteorite with an average Ni-content of 7.8%, which is identical (within error) to a previously identified meteorite called Wabar. It is possible that the Camel Charm represents a piece of Wabar that was traded to the Ababda in Egypt from its original home in Saudia Arabia. The Camel Charm is a unique meteorite from an ethnographic standpoint, with a very interesting history. It is valuable addition to the National Meteorite Collection.
Friday, February 19, 2016 - Lecture Hall, 3:30 PM
Nicolas LeCorvec, Lunar and Planetary Institute
Effects of mechanical, rheological and tectonic controls on the formation of giant radial dike systems on Venus: Insights from finite element modeling.
Radial dike systems are intriguing magmato-tectonic features occurring on Venus, Earth and Mars. For such systems to form, massive quantities of magma ascending from the mantle must be redirected laterally at shallow depths within the lithosphere over several hundred kilometers. Observations have shown different patterns from continuous fanning to subswarms of subparallel dikes. As magma ascends towards the surface, accumulation in reservoirs situated at various depths within the lithosphere is often coupled with the growth of a volcanic edifice at the surface. The stability of magma reservoirs, and therefore the generation of magmatic intrusions, is influenced by their shape, their location, the tectonic environment and the mechanical and rheological properties of the lithosphere.
Based on previous work investigating the role of flexure on the stability of magma reservoirs, we developed new models to test: 1- the role of a mechanically-layered lithosphere; 2- the role of extensional stresses; and 3- the ellipticity of magmatic reservoirs on the formation of these radial dike systems. To explore these scenarios, we used the COMSOL Multiphysics finite element package allowing us to develop: 1- 2D axisymmetric elastic models made of mantle and crustal components; 2- 3D elastic models in which an extensional stress was applied; and 3- elliptical magmatic reservoirs embedded within 2D axisymmetric elastoplastic models. Different tectonic environments were studied: lithostatic, upward flexure due to uplift consistent with a plume-derived origin and downward flexure due to the load of a volcanic edifice.
Mechanical layering within the lithosphere impacts the location of failure along a magmatic reservoir and the type of magmatic intrusions. We observe that shallow magma reservoirs in an upward flexure environment tend to produce radial dikes. Regional Extensional stresses in 3D tend to focus the location of failure along the magma reservoir, therefore limiting the formation of continuous fanning pattern. Finally, the elliptical shape of a magma reservoir favors continued expansion and increasing ellipticity, because failure at the midsection requires less overpressure as the ellipticity of the reservoir increases.
These results highlight new physical and structural controls on the formation of radial dike systems on Venus. Specifically, we can infer 1- potential crust/mantle ratios within the Venusian lithosphere; 2- the extensional stress regime linked to the formation of specific radial dike systems; and 3- the mechanisms of magma chamber growth linked to the formation of calderae observed in conjunction with radial dike systems on Venus.
Friday, February 26, 2016 - Lecture Hall, 3:30 PM
Peter James, Lamont-Doherty Earth Observatory at Columbia University
Crustal structure of the South-Pole Aitken Basin from GRAIL and LOLA
The Moon's South Pole-Aitken basin (SPA) is the largest confirmed impact basin on the Moon, and it delineates one of the ~4 major lunar terranes. The gravity and topography data from GRAIL and LOLA respectively provide an opportunity to study the structure the crust and mantle under SPA. Long-wavelength gravity and topography are sensitive to the uppermost several hundred kilometers of the lunar interior, and are consequently sensitive to mass heterogeneities in the lunar mantle. Short wavelength gravity and topography data primarily reveal the bulk densities of the crust. Remote sensing instruments such as the Moon Mineralogy Mapper have detected the presence of anorthosites, pyroxenes, and olivines in various parts of the basin, but ambiguities remain: it is not known whether surface compositions are representative of the crust as a whole, and absolute abundances of mafic components are poorly constrained. By correcting for the distribution of porosity in the lunar crust, I use gravity and topography to estimate the grain densities of various crustal features in SPA. In particular, the rings and peak-rings of basins superimposed on SPA offer an opportunity to sample compositions of materials that originated deep within SPA’s impact melt sheet.
Friday, March 4, 2016 - Lecture Hall, 3:30 PM
Nicolle Zellner, Albion College
Shock Chemistry of Simple Sugars: Production of Biologically Relevant Compounds in Impacts
The identification of over 100 different sugars, sugar acids, amino acids, and other biologically relevant molecules in the Murchison meteorite has spurred interest in the field of prebiotic chemistry. Questions regarding the origins of these compounds are many. For example, are they native to the meteorite? If so, how were they formed? Could they have been formed in the shock event that occurred when the meteorite fell to the Earth?
In this talk, I will describe our recent experiments where we explore the reactivity of two simple sugars, glycolaldehyde and dihydroxyacetone, catalyzed by mineral surfaces. I will also present the results of laboratory impact experiments where these sugars and mineral matrices were subjected to reverberated shocks from 5 GPa to >25 GPa. Our experiments show that the production of larger molecules (with up to six carbons) is accelerated under the conditions that simulate impacts by extraterrestrial objects. Scenarios for the production of these molecules via impact delivery by asteroids or comets will be explored.
Friday, March 18, 2016 - Lecture Hall, 3:30 PM
Patrick Taylor, Arecibo Observatory
Solar System Observations with the Arecibo Planetary Radar System
Arecibo Observatory in Puerto Rico houses the largest and most sensitive single-dish radio telescope and the most active and powerful planetary radar system in the world. The radar system on the 305-m William E. Gordon telescope has been used to study objects in the Solar System since its construction in 1963, from Mercury out to Saturn and all solid bodies in between. I will discuss the history of planetary radar at Arecibo and its applications to Solar System astronomy with specific attention paid to observations of near-Earth objects. Radar observations of near-Earth asteroids are critical for identifying those objects that may present a hazard to Earth and providing detailed physical characterizations in terms of size, shape, spin, and surface-property (reflectivity, polarization, geologic features and sometimes composition and density) information. In fact, radar investigations of many near-Earth objects are roughly equivalent in terms of their science content to space flyby missions, but at a cost orders of magnitude less making radar arguably the most powerful ground-based method for post-discovery characterization of the near-Earth object population.
Friday, April 8, 2016 - Lecture Hall, 3:30 PM
Julie Stopar, Arizona State University
Proximal Volcanic Deposits and an Evolving LROC-Perspective of a Dynamic Moon
Unprecedented high-resolution coverage (0.5-2 m scale images) and derived topography (2-5 m scale DTMs) from the Lunar Reconnaissance Orbiter Camera (LROC) continue to transform our understanding of lunar geology. Both impact craters and volcanic constructs are well preserved on the Moon, and LROC Narrow Angle Camera (NAC) images reveal new details of their morphology and distributions. In this talk, I will focus on my investigations of several volcanic landforms about which little detail was previously known and discuss what questions yet remain in their understanding. For example, small-area conical deposits emplaced proximal to source vents (0.5-3 km in diameter) are relatively common and widely dispersed in the maria. NAC images resolve layering in the cones that I interpret as interbedded cinder, spatter, and lava. Dark draping layers on the summits are likely late-stage spatter facies or lava remnants. Cones in the Marius Hills are larger and steeper on average than those found elsewhere, a possible consequence of increased volatiles and/or larger eruption volumes. Other morphologies signify variations in explosiveness and volatile content during or between eruptions. Cone and flow stratigraphies in the Marius Hills connote repeated eruptions from a single, long-lived source, perhaps spanning 3 billion years, suggesting persistent, regional-scale volcanism. These and other landforms are contributing to an emerging view of a more dynamic and younger Moon.
Friday, April 15, 2016 - Lecture Hall, 3:30 PM
Silvia Protopapa, University of Maryland
Volatile Reservoirs in the Outer Solar System
Over the past decade, the synergy of ground- and space-based observations, modeling efforts, and laboratory studies have highlighted vital information on the composition of the worlds in the outer solar system. I will discuss some of the latest results from New Horizons at Pluto and contrast them with emerging trends seen in other trans-Neptunian objects and comets — the primitive remnants of the planetesimal disk from which the outer planets formed. I will demonstrate how characterizing the composition of these objects improves our understanding of the primordial solar nebula and the accretion processes that led to the formation of the planets.
Wednesday, April 20, 2016 - Lecture Hall, 3:30 PM
Dominique Weis, University of British Columbia
The Fine Structure of the Hawaiian Mantle Plume Images the Earth's Deep Mantle
The origin, scale and source of mantle heterogeneities have been the subject of debate since their first documentation through the study of ocean island basalts (OIB) 50 years ago (Gast et al., 1964). One of the most common approaches is to analyze the geochemistry of oceanic basalts brought to the surface by mantle plumes, sampled either on oceanic islands or by drilling oceanic plateaus. Improved analytical precision for radiogenic isotopes, combined with statistical data treatment, has provided the finer resolution necessary for identifying small-scale geochemical variations in OIB that relate to shallow and deep plume structure. Another key factor is the acquisition of continuous datable sequences of lavas (DePaolo & Weis, 2007).
The Hawaiian mantle plume represents >80 Myr of volcanic activity in a pure oceanic setting and with a high magmatic flux. Identification of two clear geochemical trends (Loa and Kea) among Hawaiian volcanoes (Tatsumoto, 1978; Abouchami et al., 2005) in all isotope systems (Weis et al., 2011), together with the recurrence of similar isotopic signatures at >350 kyr intervals identified in the HSDP (Hawaii Scientific Drilling Project) cores, have implications for the dynamics and internal structure of the Hawaiian mantle plume conduit (Farnetani & Hofmann, 2009, 2010) and source (Farnetani et a., 2012). In this review talk, I will present a compilation of recent isotopic data for samples from shield lavas on Hawaiian volcanoes, focusing specifically on high-precision Pb isotopic data (MC-ICP-MS or DS, TS-TIMS) integrated with Sr, Nd and Hf isotopes. All isotopic systems indicate source differences for Loa- and Kea-trend volcanoes that are maintained throughout the ~1 Myr activity of each volcano and that extend back in time on all the Hawaiian Islands (~5 Ma). There is also a NE-SW gradient in isotopic compositions. The Loa-trend source is more heterogeneous in all isotope systems than the Kea-trend source by a factor of ~1.5.
When projected to the CMB, many mantle plumes occur at the edges of large low shear velocity provinces (LLSVZ) (e.g., Ritsema et al., 2004). The Hawaiian mantle plume overlies the boundary between typical Pacific lower mantle on the Kea side and a sharp, seismically defined, layer of apparently different ULVZ material that occurs on the Loa side of the plume. The geochemical differences between the Kea and Loa trends reflect preferential sampling of these two distinct sources of deep mantle material at the core-mantle boundary. Similar indications of preferential sampling at the edges of the African LLSVP are found in Kerguelen and Tristan da Cunha basalts in the Indian and Atlantic oceans, respectively. The anomalous low-velocity zones at the core–mantle boundary store geochemical heterogeneities that are enriched in recycled material (EM-I type) and are sampled by strong mantle plumes such as Hawaii and Kerguelen.
To wrap up, I will present new data for the Northwestern Hawaiian Ridge (i.e. for 42 myr of activity of the Hawaiian plume) and discuss the conditions of appearance of the Loa component and its impact on plume magmatic flux.
Friday, April 29, 2016 - Lecture Hall, 3:30 PM
Andrew Rivkin, Johns Hopkins University Applied Physics Laboratory
Water, Hydroxyl, and Ice in the Asteroid Belt
Water-and Organics-rich objects are of intense interest to the planetary science community, and are high-priority targets for spacecraft visits and sample return. However, such visits are rare commodities, and remote sensing via telescopic observations are necessary to obtain the context required for understanding spacecraft measurements. Over the past decade, we have observed hundreds of objects at wavelengths diagnostic for water and organic material. I will present our current understanding of water, hydroxyl, and ice on asteroids, including the ways these objects are and aren't represented in the meteorite collection.
Wednesday, May 4, 2016 - Hess Room - Brown Bag, 12:00 PM
Jeremie Lasue, IRAP-OMP
Internal structure of Comet 67P/Churyumov-Gerasimenko probed by the CONSERT radar on ROSETTA
During the successful landing of Philae on 67P/Churyumov-Gerasimenko, the Comet Nucleus Sounding Experiment by Radiowave Transmission (CONSERT) provided the first opportunity to investigate the internal structure of a comet nucleus. The data unambiguously showed that propagation inside the smaller lobe of the nucleus was achieved (Figure) . CONSERT also reduced the size of the uncertainty of Philae’s final landing site down to approximately 21 by 34 square meters [1, 2].
From the shape of the received signals, we can infer that the smaller lobe of 67P is fairly homogeneous on a spatial scale of tens of meters. The average permittivity obtained from the propagation delay is about 1.27, suggesting that this region has a volumetric dust/ice ratio of 0.4 to 2.6 and a porosity of 75 to 85% . From comparison with laboratory measurements made on meteorites and ice mixtures, the dust component permittivity value may be comparable to that of carbonaceous chondrites. Simulations of the signal propagation is consistent with a possible near-surface gradient of the dielectric constant decreasing with depth .
The very low dielectric constant values and homogeneity of the nucleus as constrained by CONSERT data indicates that the comet interior is primitive and has not been heavily processed. The data does not show the presence of cometesimals or large voids at the scale probed (about 10 meters), providing information about its formation and evolution in the early solar system.
Figure: Propagation of signals from Philae on the nucleus to Rosetta on its orbit.
References:  W. Kofman, et al., Science 349, aab0639-1 (2015)  A. Hérique, et al., PSS, 117, 475-484 (2015)  V. Ciarletti, et al., A&A aa26337-15, (2015)
Tuesday, June 21, 2016 - Lecture Hall, 3:30 PM
Kathleen E. Vander Kaaden, University of New Mexico, Earth and Planetary Sciences
Experimental Investigation into the Darkness of Mercury’s Surface
Prior to the return of data from the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft, the planet Mercury was thought to be depleted in volatile elements primarily due to its close proximity to the sun. Initial analyses conducted during flybys from the Mariner 10 mission confirmed the presence of atmospheric H, He, and O. Furthermore, ground-based discoveries enhanced our knowledge about Na, K, and Ca in the atmosphere as well as polar volatiles found in radar-reflective deposits. Although there was some evidence for the presence of volatiles on the surface of the planet and in the exosphere, it was not until the return of data from MESSENGER that it was discovered just how volatile rich Mercury is. We use recent results from the X-Ray Spectrometer and Gamma-Ray Spectrometer that were onboard MESSENGER to investigate the darkness of Mercury’s surface through high pressure and high temperatures experiments. Our results suggest the dark mercurian surface is likely due to a primary floatation crust on Mercury composed of graphite, produced after a global magma ocean event. Furthermore, given the highly reducing nature of Mercury (ΔIW-3 to ΔIW-7), the large core of the planet likely contains Si as the dominant light element. With higher abundances of Si in the core, our experimental investigation suggests that the core of Mercury would have saturated in carbon at low carbon abundances. Since carbon solubility in silicate melts is exceptionally low under highly reducing conditions, its exclusion from the silicate portion of the planet would have been conducive to formation of a graphite floatation crust.
Friday, July 8, 2016 - Lecture Hall, 3:30 PM
Paul O. Hayne, Geophysics and Planetary Geosciences, Jet Propulsion Laboratory
Micro Cold Traps on the Moon
Recent observations of the Moon and Mercury have confirmed basic theoretical predictions of water ice in cold traps within permanent shadows at high latitudes. However, several important aspects of the theory do not match these observations: Mercury appears to harbor massive ice deposits, whereas lunar volatiles are more dispersed or even absent in some locations; super-volatiles (CH4, CO2, methanol) are found in a surprising location on the Moon; thermal environments are heterogeneous within the permanent shadows, and volatiles do not always “follow the cold”. In this presentation, we will explore the current datasets and illustrate some of these discrepancies. In order to address the problem, I will present a new theory: micro cold traps, which collectively may be important sinks for volatiles on both the Moon and Mercury. Finally, I will show evidence for the existence of micro cold traps and discuss their possible importance for future robotic and human exploration of the Moon and beyond.
Friday, September 16, 2016 - Lecture Hall, 3:30 PM
Joseph Masiero, NASA Jet Propulsion Laboratory
NEOWISE: Mission Overview and Recent Results
The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) is
undertaking an all-sky thermal infrared survey to both discover new
near-Earth asteroids and comets, and characterize previously known
NEOs. NEOWISE provides simultaneous imaging at 3.4 and 4.6 microns,
measuring the thermal emission from NEOs and allowing their diameters
to be computed. I will discuss the techniques used for asteroid and comet
identification, focusing on the unique concerns for space telescopes,
and present an overview of recent results from this data.
Thursday, September 22, 2016 - Lecture Hall, 3:30 PM
Levke Kööp, University of Chicago
Tracing the Earliest Stages of Solar System History with Calcium-Aluminum-Rich Inclusions Found in Meteorites
Calcium-aluminum-rich inclusions (CAIs) found in primitive meteorites are the oldest dated solids that formed inside the Solar System. Their isotopic signatures facilitate a view into the nucleosynthetic inventory of the Solar System before such signatures were diluted by mixing processes in the disk.
In this talk, I will present data from a multielement isotopic study of a large number of hibonite-rich CAIs recovered from the Murchison meteorite. The isotopic properties of these CAIs are extremely variable, suggesting that they sampled different nebular reservoirs and possibly different stages in the evolution of the early Solar System. I will discuss relationships found in the dataset and how they relate to long-standing questions such as whether fresh radionuclides like 26Al were injected into the solar nebula late and what the origin of the large oxygen isotopic variations in Solar System materials is.
Friday, September 30, 2016 - Lecture Hall, 3:30 PM
Ming-Chang Liu, UCLA
The Initial 41Ca/40Ca Ratios in Two Type A Ca-Al-Rich Inclusions: Implications for the Origin of Short-Lived 41Ca
In this talk, I will present the new 41Ca-41K isotopic data of two Type A CAIs, NWA 3118 #1Nb (compact Type A) and Vigarano 3138 F8 (Fluffy Type A), from reduced CV3 chondrites. The NWA CAI is found to have carried live 41Ca at the level of (4.6±1.9)×10−9, consistent with the proposed Solar System initial 41Ca/40Ca = 4.2 × 10−9 by Liu et al. (2012). On the other hand, the Vigarano CAI does not have resolvable radiogenic 41K excesses that can be attributed to the decay of 41Ca. Combined with the 26Al data that have been reported for these two CAIs, we infer that the 41Ca distribution was not homogeneous when 26Al was widespread at the canonical level of 26Al/27Al = 5.2 × 10−5. Such a 41Ca heterogeneity can be understood under two astrophysical contexts: in- situ charged particle irradiation by the protoSun in the solar nebula that had inherited some baseline 10Be abundance from the molecular cloud, and Solar System formation in a molecular cloud enriched in 26Al and 41Ca contaminated by massive star winds. That said, more high quality 41Ca data are still needed to better understand the origin of this radionuclide.
Thursday, October 20, 2016 - Lecture Hall, 3:30 PM
Don Hood, Department of Geology and Geophysics at Louisiana State University
Assessing the Geologic Evolution of Greater Thaumasia, Mars
The chemical maps provided by the Gamma-Ray Spectrometer (GRS) instrument suite aboard the Mars Reconnaissance Orbiter allow chemical insight into the martian shallow subsurface. In this dataset, some regions show unique chemical anomalies where multiple elements deviate significantly from their average values. One such region, termed Greater Thaumasia, is characterized by overlapping signatures of K, Th, and H2O depletion, as well as Si enrichment. These chemical anomalies overlap the interesting geology of Sinai and Thaumasia Planum, the wrinkle ridge structures southwest of Thaumasia, and the inter-crater plains leading to the Argyre Basin. We use combined chemistry, mineralogy, and other remote observations to test existing models for the formation of the Greater Thaumasia region, as well as models for global magmatic evolution.