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 Georgiana Kramer (phone: 281-486-2141; e-mail: firstname.lastname@example.org) or Patricia Craig (phone: 281-486-2144; e-mail: email@example.com). A map of the Clear Lake area is available here. This schedule is subject to revision.
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The study of asteroids that present sporadic cometary activity is of fundamental importance several current problems in planetary science, such the end states of comet nuclei, the abundance of water in main belt asteroids and its role as a possible source of terrestial water. We studied the composition of the surface of asteroid (3200) Phaethon, a paradigmatic case of asteroid-comet transition objects, in order to determine its cometary or asteroidal nature. The shape of Phaethon’s visible and near-infrared spectrum is similar to that of aqueously altered CI/CM meteorites and hydrated minerals. Phaethon’s spectrum shows important differences with the few comet nuclei properly observed at these wavelengths and is similar to the spectra of other peculiar comet-asteroid transition objects. The spectral properties and dynamical properties of (3200) Phaethon support an asteroidal nature rather than a cometary one. Phaethon is more likely an "activated" asteroid, similar to the population of Main Belt Comets reported by Hsieh & Jewitt (2006), than an extinct comet.
Mesosiderites are stony-iron meteorites consisting of roughly equal amounts of silicates and metal. Mesosiderites have undergone complex secondary thermal metamorphism, and recent oxygen isotopic studies have revealed a connection to the HED meteorites. Therefore, the formation history of mesosiderites and the origin of their components remains rather enigmatic. To better understand the formation and differentiation history of the mesosiderite parent body, I carefully chose some large monogenic clasts from least metamorphosed types of mesosiderites and studied their mineralogy and geochemistry, especially focused on siderophile element abundances in the clasts. The siderophile element abundances show a full range from fractionated to unfractionated patterns, relative to chondrites. These features correlate with metamorphic degree shown by REE element abundances in phosphate minerals. I will present these results and discuss possible formation and differentiation scenarios for the mesosiderite parent body.
The Earth maintains an incomplete record of its own bombardment, but ancient rocks of the Moon, Mars, and the asteroids preserve abundant evidence of impact craters and their products that reflect how their surfaces have evolved over 4.5 billion years. I will discuss my work in characterizing impact-melt clasts in lunar and meteorite breccias and interpreting what they reveal about the bombardment history of the inner solar system.
Large Igneous Province (LIP) eruption sites of the past 300 My are highly concentrated (there is a probability of ca.1 in 7 million that randomly disposed sites would be so concentrated) vertically above the 1% slow seismic shear wave velocity contours at the CMB that define the margins of the Earth's two Large Low Shear wave Velocity Provinces (LLSVPs) and of two smaller LSVPs (Torsvik et al. G.J.Intl 2006). That observation has enabled us to pose and in some cases to attempt to answer, stimulating questions about the mantle such as: Why are the sources of mantle plumes so restricted? Have the LLSVPs been where they are now for 300 My — or possibly for very much longer? Are the LLSVPs isolated from the mantle circulation? If they are what are possible geochemical implications of that isolation? Are the LLSVPs buoyant superplumes? Why do the upward projected LLSVP footprints so closely match the elevated regions of the Geoid? Has the Geoid been where it now is for 300 My — or for very much longer?
The ancient surface of Mars displays a rich record of hydrological activity, including the extensive evaporite deposits found in Meridiani Planum by the Opportunity rover, hydrated minerals identified from orbit scattered across the planet, and the widely distributed dendritic valley networks. I will discuss the early hydrological evolution of Mars in light of our global-scale hydrological models. This work suggests that the formation of the Meridiani evaporites, the distribution of valley networks, and the observed transitions in the surface geochemistry can be understood in terms of the global-scale hydrological evolution.
Undifferentiated satellites such as Saturn's moon Rhea and Jupiter's moon Callisto can constrain the timing and duration of their accretion, the timing of formation of their parent planets, and by extension, the lifetime of the solar nebula. For Rhea and Callisto to remain partially undifferentiated at present, they must have avoided melting during formation, when accretional energy and decay of 26^Al delivered an initial burst of heat to their interiors. In general, this suggests that the satellites formed slowly, after the burn-out of the majority of 26^Al and in cool disks. Rhea can avoid melting if it forms later than 2 Myr after CAI condensation, and in a relatively cool disk (T_d < 180 K). Callisto must form in > 2 Myr and no earlier than 3 Myr after CAI's to avoid early melting. If the jovian and saturnian satellites formed in the late stages of gas giant formation, these results suggest that gas inflow to Jupiter ceased no earlier than 5 Myr after CAI's, and inflow to Saturn ceased between 2-7 Myr after CAI's.
A recent study has been sponsored by the Advanced Programs Office within NASA’s Constellation Program to examine the feasibility of sending the Crew Exploration Vehicle (CEV) to a near-Earth object (NEO). One of the significant advantages of this type of mission is that it strengthens and validates the foundational infrastructure for the Vision for Space Exploration (VSE) and Exploration Systems Architecture Study (ESAS) in the run up to the lunar sorties at the end of the next decade (~2020). Sending a human expedition to a NEO demonstrates the broad utility of the Constellation Program’s Orion CEV capsule and Ares launch systems. This mission would be the first human expedition to an interplanetary body outside of the Earth-Moon system and would help NASA regain crucial operational experience conducting human exploration missions outside of low-Earth orbit, which humanity has not attempted in nearly 40 years.
Such a mission would not only provide a great deal of technical and engineering data on spacecraft operations for future human space exploration, but would also provide the capability to conduct an in-depth scientific investigation of a NEO. Essential physical and geochemical properties of these objects can best be determined from a dedicated spacecraft. In addition, a crewed vehicle would be able to test several different sample collection techniques, and target specific areas of interest via extra-vehicular activities (EVAs) much more capably than a robotic spacecraft. Such capabilities greatly enhance any scientific return from this type of mission. Missions to NEOs would also have practical applications for resource utilization and planetary defense, two issues that will be relevant in the not-too-distant future as humanity begins to explore, understand, and utilize the solar system. These scientific and practical aspects, along with the programmatic and operational benefits of a human venture into deep space, make a mission to a NEO using Constellation systems a compelling prospect.
Mare basalts and lunar volcanic glasses currently provide the only means for directly assessing the chemical composition of the lunar interior. Highly siderophile elements in both mare basalts and leached lunar volcanic glass indicate the lunar mantle has long-term, chondritic-relative highly siderophile element ratios, but absolute abundances over twenty times lower than those in Earth’s mantle. This geochemical signature is consistent with core-mantle segregation prior to, or during giant impact, and a minor contribution of ‘late bombardment’ materials, presumably owing to the formation of relatively thick anorthositic crust, effectively isolating the lunar mantle. It is the aim of this contribution to further elucidate the inventory and behavior of HSE in the Moon and what implications this may have for the evolution of the lunar mantle and mare basalt source regions.
During NASA Extreme Environment Mission Operations (NEEMO), a crew of six Aquanauts lives aboard the National Oceanic and Atmospheric Administration (NOAA) Aquarius Underwater Laboratory off Key Largo, Florida. The crew lives in saturation for a week to ten days and conducts a variety of undersea "moon walks" to test a suite of long-duration spaceflight medical objectives as well as concepts for future lunar exploration using advanced navigation and communication equipment in support of the Constellation Program planetary exploration analog studies. Come learn how the Astromaterials Research and Exploration Science (ARES) Directorate at JSC is supporting the effort to produce a high-fidelity test-bed for studies of human planetary exploration models.
We take as our starting point the intriguing link in the history of the early Earth and the Moon revealed by the discovery that the range of ages of detrital zircons in Archean quartzites from Western Australia, from 4.37Ga to 3.90Ga, is identical to the spread in ages of zircons from breccias on the Moon. We continue with a discussion of new revelations on the age patterns of the ancient terrestrial zircons from different locations in the Archaean Yilgarn Craton and compare these with the age patterns of zircons from breccia samples from Apollo 14 and 17. We follow up on the new lunar results to describe how the comparative age patterns of zircons from the Apollo 14 and 17 lunar landing sites provide a new dimension in our understanding of the dynamics of KREEP magmatism on the Moon.
Magmatic volatile components control melting relationships, melt rheology, and degassing phenomena. Although the dominant volatile components in terrestrial magmas are H2O, CO2, and S-bearing compounds, research also demonstrates a significant role for Cl and F in magmatic and magmatic-hydrothermal processes. This talk will review constraints on magmatic abundances of Cl and F, summarize experimentally determined constraints on halogen behavior in melts and fluids, and apply the data to processes of volcanic eruption and the generation of hydrothermal mineralization.
I will describe the Huygens mission, the European contribution to the joint NASA/ESA/ASI Cassini-Huygens mission to explore the Saturnian system: I will cover its history, main design aspects, operations implementation and execution, with emphasis to the design and operational challenges and how they were resolved. A look at the results of the Huygens mission will conclude the
I will describe the Huygens mission, the European contribution to the joint NASA/ESA/ASI Cassini-Huygens mission to explore the Saturnian system: I will cover its history, main design aspects, operations implementation and execution, with emphasis to the design and operational challenges and how they were resolved. A look at the results of the Huygens mission will conclude the presentation.
Most biomolecules are "chiral", i.e. they come in left and right-handed mirror-image forms, yet life uses only one hand, e.g. only L-amino acids and not their "unnatural" D mirror images. We discuss the new field of "exochirality" (chirality outside the earth), including the findings of chiral amino acids in several meteorites, the chiral instrumentation on board the Rosetta mission to a comet, and the possible future use of chirality to find life on extra-solar planets on more sensitive successors to the Terrestrial Planet Finder mission.
Planetary cratering is a fundamental process on all solid- surfaced bodies in the solar system, including geologically active bodies like the Earth. And it was much more important during the first 600 million years of solar system history. I will discuss some diverse issues that have arisen in the last few years: (1) Why are there very few small craters (< 10 m diameter) on asteroids like Itokawa and Eros? (2) As we approach the 100th anniversary of the Tunguska event, what is the frequency (and consequences) of the influx of near-Earth objects and meteoroids < 100 m in diameter? (3) What is the role of secondary cratering (craters made by the ejecta from primary impactors) and how might that affect issues of planetary chronology? (4) What is known about the Late Heavy Bombardment on the Moon, its extent throughout the solar system, and the cratering rate during the 0.5 billion years before the LHB? I will briefly touch on some methodological and philosophical matters (e.g. why are there so many controversies concerning a subject that seems, at least superficially, to be simple and straightforward: counting holes in the ground?). And I may even mention the latest speculations about the reported cratering event on the shores of Lake Titicaca on September 15th.
The LPI's new quarterly public speaker series premiers with this talk by Dr. David Kring. Kring, one of the discoveres of the impact crater that is linked to the extinction of dinosaurs, will describe his search for the impact site and how the impact event created a global environmental catastrophe that extinguished most life on planet Earth. This presentation, which is free and open to the public, will be followed by a light reception and an opportunity to meet Dr. Kring.
Several lines of evidence, including the low density of small craters on some Martian volcanoes and the young isotopic ages of shergottite meteorites, suggest geologically recent volcanism on Mars. With the recent volcanism as an important constraint, we explore the nature of present-day mantle convection using numerical simulations with temperature-dependent and water-dependent Arrhenius viscosity. First, assuming an anhydrous Martian mantle, we calculate a thermal Rayleigh number range that best fits the observational constraints, which include the recent volcanism rate, the range of melt fractions in the shergottites, and the heat flux out of the core inferred from the absence of a magnetic dynamo. Increasing mantle water content decreases the solidus and increases both melt fraction and melting volume, thus increasing the rate of magma production. While thermal Rayleigh number (Ra), core-mantle boundary temperature (Tc-m) and water content all significantly affect magma production rate, we explore how water content affects the required Ra and (Tc-m) that meet the observed present-day magma production rate on Mars.
The long-term relaxation of topography has been a useful tool in the investigation of the thermal evolution of planets and satellites, particularly on the icy satellites of the outer solar system, where there are numerous examples of seemingly relaxed impact craters. The initial work was performed in the years following the Voyager exploration of these satellites, but this work was hampered by limited understanding of the material parameters for ice and the shape of a fresh crater. The rheology of ice and the initial shape of an icy satellite crater are now known much better, so my colleagues and I have re-explored the problem of crater relaxation. Surprisingly, the mechanics of this process are more complex than initially treated. Whereas relaxation was modeled assuming that viscous behavior dominates, our work has shown that elastic and even brittle behaviors are important. Furthermore, the remnant heat from the impact also produces an initial phase of rapid relaxation for the largest craters. In this talk, I review the mechanics of crater relaxation and discuss implications for the satellites of Jupiter and Saturn, particularly Ganymede and Dione.
Scientific drilling recently recovered continuous sections of melt bearing ejecta deposits within the impact structures Chicxulub (~180 km Ø, 65 Ma) and Chesapeake Bay (~90 km Ø, 35.5 Ma). Petrographic, geochemical and image analytical methods were used to identify formation conditions and emplacement processes of these rocks. This ground truth data of the impact cratering process is used to reconstruct physical boundary conditions for large meteorite impacts on Earth.
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