LPI Seminar Series

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:kramer@lpi.usra.edu) or Oliver White (phone: 281-486-2148; e-mail: white@lpi.usra.edu). 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.

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 2012

Monday, February 6, 2012 - Lecture Hall, 3:30 PM

Debra Hurwitz, Brown University
Lava erosion on the terrestrial planets: Using analytical models to distinguish between mechanical and thermal erosion

Evidence for effusive lava eruptions and surface flow has been observed on all terrestrial planetary bodies, but the potential for that flowing lava to erode into the surface to form channels has been widely debated. Analytical models are used to compare the potential for lava to erode three planetary surfaces by two erosion mechanisms, mechanical and thermal erosion. These models are used to simulate the formation of specific features identified as eroded lava channels on the surfaces of Mars, the Moon, and Mercury. Results provide estimates of the effusion rates, lava flow rates, fluid volumes, and erosion rates that are required to form the observed features. These values are used to determine the duration of the associated volcanic eruption as well as to identify potential source and deposition regions, putting the formation of the eroded lava channel into context of the regional geology for each planetary surface considered. Interpretations of model results can be used to constrain 1) whether lava was the most likely fluid responsible for channel formation and what the composition and viscosity of that lava was, 2) when a planet was volcanically active and how quickly lava was erupted onto the surface, and 3) how a planet might be expected to lose heat from the interior during that volcanically active period.

Friday, February 10, 2012 - Lecture Hall, 3:30 PM

D. Alex Patthoff, University of Idaho
Uncovering Icy Ocean Worlds:A Geologic History of the South Polar Terrain on Enceladus

Saturn’s small icy moon, Enceladus, has shown itself to be a surprisingly dynamic place that could act as an oasis for the development of life beyond Earth. Geyser-like plumes, young tectonic features, and relatively warm ice, discovered by the Cassini spacecraft, show that the moon is one of the most active bodies in the solar system. Most of the activity and young geologic features are concentrated in the heavily fractured region known as the south polar terrain (SPT). To explain the higher temperatures and eruptive icy plumes originating from the four largest and most prominent fractures (informally called tiger stripes) in the surface, many models implicitly assume a subsurface global liquid ocean that amplifies the tidal forces produced by the moon’s orbit around Saturn. However, direct evidence for such a body of water is not possible but indirect evidence in the surface features, predominantly fracture orientations, suggests the outer icy shell of Enceladus has rotated nonsynchronously over a global ocean and the solid interior. We show that the fracture patterns in the south-polar region are inconsistent with contemporary stress fields, but instead formed in a temporally varying global stress field related to nonsynchronous rotation (NSR) of a floating ice shell above a global liquid ocean. The fracture sets show a counterclockwise progression in orientation through time, which implies the causal SPT stress field created distinct fracture sets at different points in time. Approximately 153° of counterclockwise rotation relative to the present day surface is preserved in the fracture history of the SPT. Additionally, we have identified potential remnants of ancient tiger stripe-like fractures within the fracture sets that indicate there has been a long history of tiger stripe and plume activity on Enceladus. The present-day tiger stripes are just the latest versions of these tectonic features. Based on our evidence for NSR, new numerical modeling suggests the stresses induced by NSR may be on the order of MPa, much higher than previously modeled diurnal tidal stresses (tens to hundreds of kPa). The larger stresses that result from NSR may be the primary cause of fracturing in the SPT and the ultimate origin of the tiger stripes.

Friday, February 17, 2012 - Lecture Hall, 3:30 PM

Dr. Michael Max, Hydrate Energy International
Oceanic and Permafrost natural gas hydrate paratypes on Earth: Models for the solar system and beyond

Natural gas hydrate (NGL) occurs both in the earth’s oceans and in permafrost regimes, but in different regions of the (methane) hydrate stability field. NGH occurs in a gas hydrate stability zone (GHSZ), which is stable generally from a cold surface to a subjacent depth determined by increasing temperature. In a GHSZ, the NGH is most stable in the upper part and less stable in the lower part of the zone. The base of the GHSZ is effectively the phase boundary. In addition to understanding in considerable detail the physical chemical drivers of hydrate formation, dissolution, and dissociation, application of the NGH petroleum system holds promise of successful exploration of concentrations of economic scale. And there appears to be very large volumes of gas-in-place in NGH. The key to understanding how NGH may exist and interact with climate and potential biosystems on other bodies in the solar system (and elsewhere) may be best understood by modeling the approximate conditions on these bodies and then using earth analogue examples to further resolve the models. For cold planetary bodies such as Mars, analogues of all three types of permafrost hydrate may be found, and these may be encountered in abundance near enough to the surface to provide a natural resource to support human colonization. On icy bodies such as Europa, a marine analogue of the compound ice cryosphere - NGH stability zone may exist. NGH may be stable in the atmospheres of Jupiter and other gas giants. Because NGH and compound hydrate, which forms from a mixture of hydrate forming gases, acts to sequester natural gas from a gas flux on earth and acts as a climate moderator, it may also have this role in other bodies in the solar system. On Titan, water and the abundant natural gases may generate NGH as part of a materials redistribution system involving water and hydrate-forming gases.

Friday, February 24, 2012 - Lecture Hall, 3:30 PM

Paul Byrne, Carnegie Institution of Washington
Volcanism on Mercury: Insights from Orbit

Since its insertion into orbit around Mercury in March 2011, the MESSENGER spacecraft has returned a wealth of information about the volcanic landforms and history of the innermost planet. Extensive surface volcanism was hypothesized after the early Mariner 10 flybys in the 1970s; now, MESSENGER has confirmed a volcanic origin for smooth, vast expanses of plains that differ in color from and embay surrounding terrain, particularly at high northern latitudes. With a global image basemap at 250 m/pixel almost complete, a planet-wide survey of volcanism on Mercury is now possible. This presentation will summarize the current state of knowledge of volcanism on Mercury after almost a year of orbital observations by the MESSENGER spacecraft. In contrast to Earth, the Moon, Mars, and Venus, no large centers of concentrated igneous activity are visible, nor are large shield volcanoes, calderas, or other significant volcanic constructs. The expansive smooth plains observed across the planet, and particularly those northern deposits, may represent the largest scale of surface volcanism. Smaller features, such as sinuous rilles commonly observed on the Moon and Mars, are also largely absent. Those small-scale features that are present include rimless depressions scattered across the planet, which appear to be the sources of pyroclastic deposits. There is also a curious assemblage of channel-like landforms proximal to the northern plains that resemble surface flow features on Earth and Mars, and which may be the product of erosion by high-volume, high-temperature lavas. Finally, the documented contractional history of Mercury, evidenced by abundant thrust faults and related tectonic structures, precludes significant upper-crustal extension and the emplacement of shallow-level igneous intrusions. Accordingly, there are few sites where shallow intrusive activity has unequivocally occurred, suggesting that much of Mercury's surface volcanism is sourced from significant depths.

 

 

facebook