LPI Seminar Series 2013

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 Takafumi Niihara (phone: 281-486-2169; e-mail:niihara@lpi.usra.edu) or Ross Potter (phone: 281-486-2144; e-mail: potter@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.

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, Chm, 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, 12:00 AM

Andrew Dombard, University of Illinois at Chicago
Icy MoonThe 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
Craters

Friday, May 31, 2013 - Lecture Hall, 3:30 PM

Tom Zega, University of Arizona

June 2013

Friday, June 14, 2013 - Lecture Hall, 3:30 PM

Kelsi Singer, Washington University, St. Louis