2009 PSI Retreat Abstracts

Terrestrial Analogs for Geochemical Variability

Investigations of the origin of the martian sulfate and phyllosilicate deposits have led to the hypothesis that there was a marked, global-scale change in the Mars environment from circum-neutral pH aqueous alteration in the Noachian to an acidic evaporitic system in the late Noachian to Hesperian. However, terrestrial studies suggest that two different geochemical systems need not be invoked to explain such geochemical variation. Terrestrial environments exist where the coexistence of these two mineral groups represent local geochemical variability and both acidic and alkaline chemistries coexist separated vertically and/or laterally by only a few tens of meters. Examples of such environments include acidic dry lakes in Western Australia, hot springs in Yellowstone and high altitude volcanic lakes in Hawaii. Studies of the coetaneous formation of phyllosilicates and sulfates and the ability to detect these environments remotely aids in the understanding of Mars' complex and diverse hydrological history.

SpILS: Spatial Indices for Investigating Landscape Systems

This presentation is an overview of planetary analogue studies using spatial statistical analysis, mapping and modelling within a GIS. Examples from volcanic and aeolian landscapes will be used to demonstrate the concept of landscape self-organization and how such method is used to further interpret the geographic, geologic, geomorphic, and climatic history of planetary surfaces.

Meteorite Petrology from Chondrites to Mars

Chondrites provide samples of the earliest solid materials in our solar system, and evidence of the earliest parent body (i.e. geological) processes. Primitive achondrites reveal details of the earliest melting and differentiation processes. The HED and martian meteorites record more extensive differentiation on larger bodies. I apply my skills as a petrologist to all stages of this evolution.

Photometry? Why Bother?

"Photometry" is the term used to describe the variations in reflectance brightness as a function of illumination and viewing geometries. The measure of the variation in brightness as a function of these geometries can be modeled to derive surface properties, such as porosity, roughness, particle albedos and scattering functions. However, the modeling also serves as a mechanism for calibrating observations to a common illumination and viewing geometry. Interpretations of color and spectral measurements are quite dependent on the quality of this photometric calibration. This presentation provides examples of the magnitude of this dependence.

Infrared Analyses of Phyllosilicate and Sulfate Deposits on Mars: Recent Results

The overarching goal of my research program at PSI is to understand how aqueous alteration processes on Mars have occurred through different epochs in the planet's history. In recent work, I have been using thermal infrared emission spectra from the TES instrument along with near infrared data from the OMEGA and CRISM instruments to explore in more detail the mineralogy of phyllosilicate deposits in the ancient crust. Based on OMEGA and CRISM data, the phyllosilicate deposits are largely composed of Fe/Mg-rich smectites. Recent TES results indicate that the phyllosilicates are most similar to Fe2+ clay minerals, and may be poorly crystalline. The two largest phyllosilicate deposits have very different characteristics from the TES perspective. In the Mawrth Vallis area, the phyllosilicates occur within layered rocks that are dominated by amorphous silica and feldspars. In the Nili Fossae region, phyllosilicates occur within layered rocks, massive bedrock, impact ejecta, and crater central peaks, all dominated by a combination of pyroxene and feldspar. The key difference is that the Mawrth Vallis deposits appear to be much more intensely altered, or altered from a fundamentally different protolith. Previously, TES data have provided ambiguous results in regard to phyllosilicate occurrences. But, through careful analysis in the Nili Fossae region, I have been able to develop a spectral index for the identification and mapping of phyllosilicates in this region and beyond. Ongoing work is showing widespread occurrences of phyllosilciates throughout the ancient crust from thermal infrared data for the first time. Global mapping is underway.

A different project focuses on the origin of Martian sulfate deposits. OMEGA and CRISM have shown the presence of layered sulfate deposits in many locations on Mars, and exploration by the Opportunity rover has revealed the chemical details of one of these deposits in the Meridiani Planum region. Existing ideas for the origin for the Meridiani deposits include: a) the MER team playa hypothesis (Squyres et al., 2006), b) the volcanogenic hypothesis (McCollom and Hynek, 2005), and c) impact hypothesis (Knauth and Burt, 2005). All of these ideas present certain strengths and weaknesses, but the greatest weakness in the most popular model (playa model) is the lack of explanation for: the scale of the deposits, the origin of significant amounts of extremely acidic fluids in a basaltic crust, and the origin of cation-conservative weathering (essentially all of the depsosits have the chemistry of basalt + sulfur). Niles and Michalski (2009) recently proposed a new model in which sulfate deposits at Meridiani Planum, and perhaps throughout the globe, were formed originally within massive ice deposits. In this model, acidic aerosols and silicate dust were trapped in low-latitude ice deposits on ancient Mars. Extremely acidic fluids formed in small pockets within the ice through radiative heating of the ice-dust mixture, and freezing point depression by the acid. Weathering of the silicate dust occurred on a massive scale, but each grain was weathered within an isolated microenvironment favorable for a cation conservative weathering style. After the ice sublimated, massive deposits of altered, fine-grained dust and sand were reworked by eolian processes into layered deposits that eventually underwent limited diagenesis under very low water/rock ratios. We have a recently funded MDAP project aimed to test for the geologic implications of this model throughout the various occurrence of sulfate deposits on Mars.

Squyres, S. et al. 2006. Two years at Meridiani Planum: Results from the Opportunity Rover. Science 313. 1403-1407.

McCollom, T. M., and B. M Hynek 2005. A volcanic environment for bedrock diagenesis at Meridiani Planum. Nature 438. 1129-1131.

Knauth, L. P., D. M. Burt, and and K. H. Wohletz 2005. Impact origin of sediments at the Opportunity landing site on Mars. Nature 438. 1123-1128.

Niles, P. B. and J. Michalski 2009. Meridiani Planum sediments on Mars formed through weathering in massive ice deposits. Nature Geoscience 2. 215-220.

Advances in Producing Optical Constants for Planetary Scientists

Optical constants, or wavelength-dependent representations of refractive and absorptive properties, of minerals in are essential inputs to radiative transfer algorithms used in many subfields of planetary science. Transforming optical constants and particle assumptions into modeled spectra allows us to compare with spacecraft data and constrain physical properties such as sizes, shapes, compositions, and abundances of dust and ice grains in Solar System and interstellar/circumstellar environments and, in turn, infer formation and evolution histories. This talk provides an "in-service" for planetary scientists on where these fundamental quantities come from and describes recent projects and local efforts to increase production and availability of optical constants.

Cosmic Rays: Scientific Tools / Space Hazards

The energetic particles in space (so-called "cosmic rays") and their interactions will be quickly reviewed. There are many products that cosmic rays make in solar-system matter that are used for scientific studies. These include cosmic-ray-produced nuclides (used to determine ages and sizes of exposed objects) and gamma rays and neutrons (used to make elemental maps of planetary surfaces). Some energetic particles, especially during very intense solar particle events, can be serious radiation hazards to people, spacecraft, and instruments. The modern and ancient records of these particles have been studied.

The Near-Earth Object Surveillance Satellite: NEO Science on a Shoestring

The Near-Earth Object Surveillance Satellite (NEOSSat) mission is funded by the Canadian Space Agency (CSA) and Defense Research and Development Canada (DRDC) with support for US Science Team members provided by NASA's Lunar and Planetary Science US Principle Investigator program (LPS USPI). Launch is currently scheduled for early 2011.

The NEOSSat mission represents the first comprehensive, synoptic, space-based, visual imagery survey over a large region of the sky and will concentrate on regions of the sky not well-suited to observing from the ground. In particular, it will more efficiently search near-Sun regions (to within 45-deg of the Sun) than ground-based systems. NEOSSat is a dual use mission and will also track high altitude satellites and space debris.

NEOSSat is designed to observe about half the NEOs, with diameters greater than 1 km, in Aten-class orbits, and about a third of the Atira population in this size range, within approximately three years of launch.

Extracting paleo-environmental constraints from clay-bearing assemblages on Mars

As recorders of interactions between the atmosphere, hydrosphere and lithosphere, clay minerals participate in all aspects of the rock cycle on Earth and the same may be true for ancient Mars. Orbital data have already revealed complex clay-bearing stratigraphy in the Mawrth Vallis and Nili Fossae regions. But the challenge for the MSL mission will be to unravel complex in-situ data to discern the origin of chemical sediments and weathering products. Experimental approaches toward martian weathering and low-temperature clay generation will aid in using martian clay-bearing assemblages to extract paleo-environmental constraints in ancient martian terrains.