LPI Seminar Series 2014
Effective January 1, 2011, LPI seminars will be held on Fridays.
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 Yann Sonzogni (phone: 281-486-2199; e-mail:email@example.com) or Debra Hurwitz (phone: 281-486-2116; e-mail: firstname.lastname@example.org). A map of the Clear Lake area (PDF format) is available here. The Acrobat Reader 8.0 is available from Adobe. This schedule is subject to revision.
- Friday, January 10, 2014 - Lecture Hall, 3:30 PM
Francesca Scipioni - Italian Space Agency
Spectroscopic Classification and Investigation of Terrain Units of Saturn's Icy Moons
In my PhD work, I have focused on the study of Saturn's icy satellites Dione and Rhea using data acquired in the infrared spectral range by the Cassini/VIMS imaging spectrometer. The surfaces of the main Saturnian icy moons are composed primarily by water ice, with a minor percentage of non-water-ice material whose composition is still debated and whose distribution is not uniform across the satellites’ surface. The differences in contaminants’ composition, water-ice abundance and regolith grain size are revealed by variations in spectral profiles, which are bounded both to exogenic (micrometeoroids and particles coming from rings or interplanetary dust) and endogenic (cry-volcanism, tectonic activity) processes. The only way to discern between them and, in turn, to understand how each satellite evolved, is to investigate the distribution of contaminants and water-ice on the moons’ surfaces. In order to identify different terrain units on the two satellites’ surface we applied the Spectral Angle Mapper (SAM) classification technique to Dione’s and Rhea’s hyperspectral images acquired by VIMS in the infrared range. On a relatively limited portion of the surface of Dione and Rhea we first identified nine and eight spectral endmembers respectively, corresponding to as many terrain units, which mostly distinguish for water ice abundance and ice grain size. We then used these endmembers in SAM to achieve a comprehensive classification of the entire surface. The analysis of the infrared spectra returned by VIMS shows that different regions of Dione and Rhea have variations in water ice bands depths, in average ice grain size, and in the concentration of contaminants, such as CO2 and hydrocarbons, which are clearly connected to morphological and geological structures. Generally, the spectral units that classify optically dark terrains are those showing suppressed water ice bands, a finer ice grain size and a higher concentration of carbon dioxide. Conversely, spectral units labeling brighter regions have deeper water ice absorption bands, higher albedo and a smaller concentration of contaminants. Finally, we performed a comparison between Rhea and Dione, to highlight different magnitudes of space weathering effects in the icy satellites as a function of the distance.
- Friday, January 24, 2014 - Lecture Hall, 3:30 PM
Robert Herrick, University of Alaska Fairbanks
The Big Picture for the Geologic History of Venus - Where Things Stand and Future Exploration
2014 marks 25 years since NASA last launched a mission to the planet Venus. Analysis of the geologic history of the planet has progressed since the initial post-Magellan flurry, and a couple of relatively mature world views of the planet's geologic history have developed. I will discuss a handful of key observations that constrain the big picture, and I will evaluate how compatible each observation is with the existing world views. I will argue that we cannot rule out either viewpoint with existing data, and I will discuss what new data would be most effective for distinguishing between existing hypotheses.
- Friday, January 31, 2014 - Lecture Hall, 3:30 PM
Peter Isaacson, Hawaii Institute of Geophysics and Planetology
Provenance of Lunar Meteorites from Samples and Spectroscopy
The returned Apollo and Luna sample collections present an incomplete view of lunar geology because of their restricted geographic coverage. Lunar meteorites are thus an important resource for lunar science, as they provide a more global sampling of the lunar crust than that available from the Apollo and Luna samples. In particular, they likely provide samples of the farside feldspathic highlands, which are not represented in the returned sample collections. However, the lunar meteorites are of limited utility due to their uncertain provenance and geologic context. In this talk, I will present results from laboratory studies of feldspathic lunar meteorite samples and from global remote sensing studies of the lunar surface. By combining these approaches, we place new constraints on the provenance of these samples. While this approach does not identify specific “source craters”, it provides regional-scale geologic context for these important samples.
- Friday, February 28, 2014 - Lecture Hall, 3:30 PM
Jeff Andrews-Hanna, Colorado School of Mines
The Early Magmatic and Tectonic History of the Moon as Revealed by GRAIL
The geological record of the earliest history of the Moon is poorly preserved as a result of the heavy impact bombardment of the surface prior to 3.7 Ga. However, the signatures of early lunar evolution are preserved in the subsurface. Recent data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission is providing a view of the lunar subsurface at unprecedented resolution. Linear gravity anomalies reveal a population of ancient igneous intrusions that likely formed during an early period of thermal expansion of the Moon, providing an important constraint on lunar formation. Later intrusive activity was dominated by the formation of circular or arcuate dikes within the ring structures surrounding the major impact basins. In the absence of ring dikes, the gravitational signatures of tectonic offsets across the rings reveal the nature of the basin ring tectonics. The largest magmatic-tectonic structure revealed by GRAIL is a quasi-rectangular set of linear density anomalies ~2500 km in diameter, encompassing the Procellarum region on the lunar nearside. The gravitational signatures of the Procellarum border structures are consistent with volcanically flooded rift valleys, formed by extension driven by the gradual cooling and contraction of the Procellarum KREEP terrain. These and other observations from GRAIL are shedding new light on the early history of Earth's nearest neighbor.
- Friday, March 7, 2014 - Lecture Hall, 3:30 PM
Francis Albarède, Ecole Nationale Supérieure, France
A New Volatility Scale for the Earth-Moon System and the Status of Water in the Moon
The notion of a dry Moon has recently been challenged by the discovery of high water contents in lunar apatites and in melt inclusions within olivine crystals from two pyroclastic glasses. However, these water contents were determined on lithologies that are rare on the lunar surface. We measured the Zn content, a highly volatile element, of mineral and rock fragments in lunar soils collected during Apollo missions, which average over the surface of the Moon. We show here that the Moon is significantly more depleted in Zn than the Earth. Combining Zn with existing K and Rb data on similar rocks allows us to anchor a new volatility scale based on the bond energy of non-siderophile elements in their condensed phases. Extrapolating the volatility curve to H shows that the bulk of the lunar interior must be dry (≤1 ppm). This contrasts with the water content of the mantle sources of pyroclastic glasses, inferred to contain up to ~40 ppm water based on H2O/Ce ratios. These observations are best reconciled if pyroclastic glasses derive from localized water-rich heterogeneities in a dominantly dry lunar interior.
- Friday, April 4, 2014 - Hess Room, 3:30 PM
Benjamin Greenhagen, Jet Propulsion Laboratory
Properties of the Lunar Regolith Revealed by the Diviner Lunar Radiometer
The Diviner Lunar Radiometer, onboard the Lunar Reconnaissance Orbiter, is the first multispectral thermal instrument to globally map the surface of the Moon. Diviner’s unprecedented and growing dataset is revealing the extreme nature of the lunar thermal environment, thermophysical properties, and surface composition. In this talk I will address each of these three topics, with emphasis on my contributions to the surface compositional and thermophysical investigations. Additionally, I will describe the legacy of Diviner for future opportunities to explore other airless solar system bodies using thermal emission techniques.
- Friday, April 11, 2014 - Lecture Hall, 3:30 PM
Karl Mitchell, Jet Propulsion Laboratory
Planetary Volcanism: Environmental Effects on Eruption Style
Volcanism is a common occurrence on planetary bodies, including asteroids as well as rocky and icy planets and moons, and on some worlds is both the dominant mode of heat transport to planetary surfaces and the main resurfacing mechanism. Dr Mitchell will discuss the dynamics of volcanic eruptions, how planetary environments modulate the expression of volcanism, and how volcanic features can be used to give insights into the planetary interior.
- Friday, April 25, 2014 - Lecture Hall, 3:30 PM
Claire McLeod, University of Houston
Constraints on the Formation Age and Evolution of the Moon from 142Nd-143Nd Systematics of Apollo 12 Basalts
The Moon likely formed as a result of a giant impact between proto-Earth and another large body. The timing of this event and the subsequent lunar differentiation timescales are actively debated. New high-precision Nd isotope data for Apollo mare basalts are used to evaluate the Low-Ti, High-Ti and KREEP mantle source reservoirs within the context of lunar formation and evolution. The resulting models are assessed using both reported 146Sm half-lives (68 and 103 Myr). The linear relationship defined by 142Nd-143Nd systematics does not represent multi-component mixing and is interpreted as an isochron recording a mantle closure age for the Sm-Nd system in the Moon. Using a chondritic source model with present day μ142Nd of -7.3, the mare basalt mantle source reservoirs closed at 4.45+10-09 Ga (t½ 146Sm = 68 Myr) or 4.39+16-14 Ga (t½ 146Sm = 103 Myr). In a superchondritic, 2-stage evolution model with present day μ142Nd of 0, mantle source closure ages are constrained to 4.41+10-08 (t½ 146Sm = 68 Myr) or 4.34+15-14 Ga (t½ 146Sm = 103 Myr). The lunar mantle source reservoir closure ages <4.5 Ga may be reconciled in 3 potential scenarios. First, the Moon formed ca. 4.55 to 4.47 Ga and small amounts of residual melts were sustained within a crystallizing lunar magma ocean (LMO) for up to c. 200 Myr from tidal heating or asymmetric LMO evolution. Second, the LMO crystallized rapidly after early Moon formation. The later Sm-Nd mantle closure age represents resetting of isotope systematics. This may have resulted from a global wide remelting event. Third, the Moon formed later than currently favored models indicate, such that the lunar mantle closure age is near or at the time of lunar formation. While current Earth-Moon formation constraints cannot exclusively advocate or dismiss any of these models, the fact that U-Pb ages and Hf isotopes for Jack Hills zircons from Australia are best explained by an Earth that re-equilibrated at 4.4 Ga or earlier following the Moon-forming impact, does not favor a later forming Moon. If magma oceans crystallize in a few million years as currently advocated, then a global resetting, possibly by a large impact at 4.40 to 4.34 Ga, such as that which formed the South Pole Aitken Basin, best explains the late mantle closure age for the coupled Sm-Nd isotope systematics presented here.