2001 Annual Science Report
Arizona State University Reporting | JUL 2000 – JUN 2001
Exploring Mars for Past or Present Life
Exploring Mars for Past or Present Life (dm)
This research project seeks to promote the astrobiological exploration of Mars through planetary exploration and terrestrial analog studies. Over the past year, efforts have been focused in three major areas: 1) Continued orbital mapping of the martian surface in the mid-infrared in search of aqueous mineral deposits formed earlier in martian history when water was present at the surface (such deposits are important targets for surface exploration to search for a record of prebiotic chemistry and /or fossil biosignatures of martian life). 2) Remote sensing analog studies of evaporite basins on the Earth to establish spatial and spectral resolution thresholds for the detection of aqueous minerals from Mars orbit. 3) Site selection for future landed missions to explore for past or present martian life. Progress in each of these areas is discussed below.
1) Exploration for aqueous mineral signatures was continued the past year using data from the Thermal Emission Spectrometer (TES), presently mapping in Mars orbit. A substantial effort was made to define the distribution of coarse-grained (specular) hematite detected last year. This mineral is the most compelling aqueous mineral signature so far discovered at Mars. Specular hematite has now been detected at three sites: Sinus Meridiani, Aram Chaos and Candor Chasma. These results have established the potential importance of specular hematite as a pathfinder mineral for ancient aqueous environments on Mars. The largest hematite deposit discovered so far is located at Sinus Meridiani. This place has emerged as a leading candidate landing site for landed missions to be launched in 2003. Another important result concerns the origin of putative paleolake deposits at a site known as White Rock. Previous authors have suggested this deposit to be a lacustrine evaporite based on geological setting and albedo. Evaporites hold obvious interest for martian astrobiology. Analysis of the TES data suggested an absence of aqueous minerals, but is more consistent with an aeolian origin, thus calling into question the hypothesis of an aqueous origin for White Rock.
2) We have completed field work for remote sensing analog studies in the Badwater Basin of Death Valley. The field component involved the collection of ground spectra using portable spectrometers. We also made significant progress in processing several infrared remote sensing data sets (AVIRIS, MASTER and ASTER) for the study area. This was accomplished using ENVI, a remote sensing analytical software. Analysis involved developing sound atmospheric corrections and binning measurements from the high resolution data to achieve spatial resolutions comparable to TES and THEMIS. We then ran classification algorithms, including multivariate statistical analyses that allowed us to produce mineral maps of the end member compositions at spatial resolutions for TES and THEMIS. These end-member maps were then compared to spectral libraries to predict the distribution of key aqueous mineral groups, such as carbonates, sulfates and borates. The main conclusion was that while TES spatial resolution of 3 km/pixel appears too coarse to reliably detect these minerals, they are clearly detected at the 100 m/pixel spatial resolution of THEMIS (presently in route to Mars). Analog comparisons are still incomplete in that A) we have yet to model the effects of the lower spectral resolution of THEMIS on detectability and B) we still need to complete ground truth studies to establish what minerals are actually present and in whatabundances. This last year we completed the field work for the ground truth component of the study, and most of the lab work. Lab work involved X-ray diffraction analysis of field samples and lab spectral analysis using a TES analog instrument. We are close to completing thin section petrographic analyses that will establish actual mineral abundances through statistical point counting methods.
3) Site selection for upcoming Mars missions is an important aspect of our research, and the past year we have focused this effort in two areas: A) Site identification and characterization for the 2003 mission to explore for ancient aqueous sediments and B) Exploration for high latitude polar sites where recent volcanism and associated hydrothermal activity may have occurred. We have now completed a 1 : 2M scale photomosaic and geologic map of the Elysium Basin â?? Terra Cimmeria region of Mars, an area which shows evidence of a prolonged aqueous sedimentary history. The goal is to describe the detailed hydrological history of the area and compare it to other similar-aged terrains previously mapped by others. Included within the map area is Gusev crater, an important astrobiological site we advocated at the 2003 landing site workshop in January and which has now been short-listed as a potential landing site for the 2003 mission. The second aspect of the site selection work involves the exploration for sites of volcano-ice interaction along the margins of the North Polar Cap of Mars. This past year we completed reconnaissance of the North Polar region, examining all available Viking and MOC images. For this work we relied heavily on use of the Space Photography Lab an imaging archive located on the ASU campus. This work resulted in the identification of three major sites, one a small volcanic field, with associated outflow channels, another site we interpret to be a pseudocrater field where explosive volcanism occurred as volcanic flows were erupted onto ground ice, and an alluvial plain in the Chasma Boreale region thought to have formed by subglacial outfloods. Current work is focused on obtaining topographic (MOLA) data for each of the sites above and producing integrated data sets as a basis for detailed mapping. The sites we have discovered are suspect hydrothermal environments where subsurface ecosystems may have been sustained for a prolonged period. Thus, they are considered good places for future landed missions to explore for biosignatures sequestered in ground ice.
PROJECT MEMBERS:Philip Christensen
RELATED OBJECTIVES:Objective 5.0
Describe the sequences of causes and effects associated with the development of Earth's early biosphere and the global environment.
Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars.
Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars, especially the habitable ones.
Define climatological and geological effects upon the limits of habitable zones around the Sun and other stars to help define the frequency of habitable planets in the universe.