2010 Annual Research Report

  

 Baldridge worked on a number of projects in 2010. They included:

 

Mapping geochemical variability in Australian acidic playa lakes with HyMAP data during 2010.

 

Terrestrial playa lakes are considered important potential analogs for paleolake basins proposed for Mars.  Playas occur in closed drainage basins with high evaporation rates and are usually subject to seasonal alternating wet-dry. Extensive salt crusts are formed by the evaporation of surface and groundwater in playa basins.  More specifically, acid saline lakes in Western Australia have been recognized as important chemical terrestrial analogs for aqueous mineral formation and geochemical variability on Mars.  In these systems large pH and salinity differences are observed both laterally and vertically of scales of a few tens of meters.  The variability in these lakes has been offered as an alternate formation mechanism for some of the phyllosilicates and sulfates on Mars, suggesting that these different mineral types may be separated by chemical gradients rather than temporal boundaries.

  

The primary and alteration mineralogy associated with acidic saline systems are spectrally distinct and usually have good exposures.  Multispectral remote sensing has been successfully used in the past to determine the detectability of evaporite mineralogy in the mid-infrared at the spatial resolution of instruments in orbit at Mars.  In the acidic saline lakes, it is important not only to understand the types of minerals present, but also their lateral distribution and occurrence.  Using VIS/NIR hyperspectral data in similar wavelength ranges as currently being investigated on Mars by the OMEGA and CRISM instruments, spectral mapping for two acidic saline playa regions in Western Australia, the Lake Brown/Chandler/Campion system and Lake Gilmore was performed.  Earth analogue investigations are useful, as they offer the opportunity to ground-truth mineral identifications and determine if known geochemical variability on the ground can be detected remotely.  This project was designed to investigate the ability of hyperspectral airborne data to detect remotely the associated geochemical variability of an acidic saline playa system in a Mars analogue environment and to determine the extent of the expression of surface variability, which may not be easily accessible in the field.

 

Phyllosilicate and Sulfate Layering in Interplaya Dunes; Analogs for Mars Intracrater Deposits

 

Data returned from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) indicate that the central sediment mounds in  Gale Crater contain smectite clays and sulfates.  The clay-bearing units in this and in similar crater deposits commonly occur stratigraphically beneath sulfates and this stratigraphic relationship is cited for deposits elsewhere on Mars as evidence of separate and temporally distinct geochemical environments on Mars. 

To evaluate the co-occurrences of phyllosilicates and sulfates on Earth to better understand similar environments on Mars, we have obtained airborne hyperspectral data from playa lakes in southern Western Australia.  Mineral maps derived from these data indicate that layered phyllosilicates and sulfates are concentrated in the central playa as aeolian features.  The sequences of clay and salt minerals may be analogous to the thick sequences of layered, crater-hosted martian sedimentary materials and may be applicable to larger sedimentary deposits on Mars as well.

 

Workshops in Science Education and Resources  

 

As part of Project WISER, a series of professional development workshops targeting elementary and middle school teachers in Tucson, AZ, we are delveloping a series of instructional rock kits and hands on learning activities for teachers, students and the public and a web based Ask-an-Expert tool focused on areas of expertise of PSI scientists.

The Ask-an-Expert web-based tool has been launched that will allow users to submit questions that will be answered by PSI experts.  Responses are emailed and also posted on the web as a FAQ. We are also cataloging and posting as FAQs questions asked by teachers during our professional development workshops.

To date, five of seven workshop topics have been developed with two corresponding rock kits.  The current focus is the development of the Volcanoes in the Solar System and Deserts in the Solar System workshops, each with corresponding activities and rock kits.  Additionally, the Deserts in the Solar System topic include a section on local Tucson (Sonoran Desert) geology that complements the ongoing collaborations with the Laurel Clark Earth Camp Experience.

 

Laboratory and Remotely Sensed Spectroscopic Characterization of Chlorides

 

Recent results from investigations using the Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS) show martian surfaces with spectral properties that appear to be generally consistent with chlorides.  However, chlorides have a relatively unique TIR spectral behavior, including low emissivity and transparency, that is different than that of most rock-forming minerals.  This behavior is not well understood, in part due to a general deficiency of systematic empirical and laboratory studies to characterize the spectral properties of these minerals.  

In this study we use a combination of laboratory, theoretical, and field studies for the purpose of establishing a framework for thermal infrared (TIR) spectroscopic investigations of chlorides. In order to accomplish this, the effects of the unusual spectral behavior of chlorides need to be well defined and the theory well understood to apply laboratory, field, and theoretical investigations to remote measurements made of the martian surface. Specifically we will: 1) Obtain and validate a collection of various chloride minerals expected to be present on Mars, 2) determine the spectral properties of the samples including reflectance, emissivity, and transparency, 3) characterize the spectral mixing behavior of chlorides with silicates and sulfates, and 4) develop methods for applying laboratory measurements to the interpretation of Martian observations.  The knowledge gained from laboratory and theoretical studies will be validated using terrestrial field and remote spectroscopic measurements of natural surfaces that contain chlorides, allowing us to assess our ability to accurately interpret the presence of chlorides on the Martian surface.

 

Aqueous Mineralogy Revealed in Earlier Mars Odyssey Orbit Time Mid-IR Data

 

The Thermal Emission Imaging System (THEMIS) has been in orbit at Mars since early 2002.  A primary objective of the THEMIS experiment is to identify minerals associated with hydrothermal and subaqueous environments including carbonates, clays, chlorides, silica and sulfates.  Of these, THEMIS data have thus far supported the presence of clays, silica-rich deposits and chlorides, but have not provided evidence for the presence of sulfates.  Given extensive morphological evidence for aqueous surface processes on Mars and the long-standing expectation that sulfates should be a dominant alteration product at the Martian surface this null result is surprising.  It is especially puzzling given the detection of sulfates in the visible/near-infrared (VNIR) by the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite´ (OMEGA) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and surface detections by the Miniature Thermal Emission Spectrometer (mini-TES) and Mossbauer Spectrometer.

The extended mission proposal for THEMIS on Mars Odyssey suggests that the detection of all minerals may be enhanced by improvements to the THEMIS signal-to-noise ratio (SNR) that would be achieved by acquiring additional data at earlier local times and thus at warmer temperatures.

To enhance surface observations the THEMIS team proposed that the orbit be moved to 3:45 LMST.  The maneuver that brought Odyssey to this orbit began in early 2009 and allowed for a period during summer 2009 with LMST of ~3PM and surface temperatures 20 degrees warmer than previously observed.

Here we examine sites on Mars in which VNIR data have revealed aqueous minerals including sulfates and THEMIS data were collected when the earlier orbit time coincided with the Martian local summer resulting in warm surface temperatures.  These sites include Columbus crater and Cross crater in Terra Sirenum and Aram Chaos.

  

 

Papers:

 

Brown, A.J., S.J. Hook, A.M. Baldridge, J.F. Crowley, N.T. Bridges, B.J. Thomson, G.M. Marion, C.R. de Souza Filho, J.L. Bishop, 2010.  Hydrothermal formation of Clay-Carbonate alteration assemblages in the Nili Fossae region of Mars, Earth and Planetary Science Letters, 297, 1-2, 174-182.

 

Hulley, G.C., S.J. Hook, A.M. Baldridge, Investigating the effects of soil moisture on thermal infrared land surface temperature and emissivity using satellite retrievals and laboratory measurements, Remote Sensing of Environment, Volume 114, Issue 7, 15 July 2010, Pages 1480-1493