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Monday, October 11, 2004

Review of Present MEPAG Goals and Objectives Related to Early Mars

David W. Beaty, Jet Propulsion Laboratory, Pasadena

Summary: As noted in the first MEPAG goals report, completion of all the investigations will require decades of studying Mars. Many investigations may never be truly complete (even if they have a high priority). Thus, evaluations of prospective missions should be based on how well the investigations are addressed. While priorities should influence which investigations are conducted first, they should not necessarily be done serially, as many other factors come into play in the overall Mars Program. On the other hand, forming a scientific consensus to identify cases where one investigation should be done before another is critical to mission planning. The advice of individual scientists is too easily discounted by HQ because of conflict of interest concerns. Consensus advice from multi-disciplinary groups of scientists has proven much more effective at influencing decisions.

Run Time: 13:03   Bit Rate: 37 kbps
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Accretion, Bulk Composition and Volatile Inventories

Michael J. Drake, University of Arizona

Mars formed about 4.55 Ga ago in the same general region as Earth. Dynamical studies suggest substantial mixing of material in the inner solar system, yet Earth, Mars, and the asteroids have distinctive compositions. Mars like Earth underwent a magma ocean epoch. The Martian atmosphere and hydrosphere outgassed within 100 my of nucleosynthesis of 129I. Isotopic measurements of Martian meteorites point to accretion beginning about 4.55 Ga ago and taking a few tens of millions of years to complete. This growth rate was sufficient to melt the outer portion of Mars, perhaps repeatedly, to an apparent depth of 60-90 kbar. This conclusion is based on the ability to fit moderately siderophile element abundances inferred for the Martian mantle from Martian meteorites to a model in which metal equilibrates with molten silicate at the base of a deep magma ocean.

Run Time: 19:52   Bit Rate: 34 kbps
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The First Billion Years of Martian History as Seen from the SNC Meteorites

John H. Jones, Johnson Space Center, Houston

There are currently 32 known, distinct samples of Mars that have been liberated from that planet by impacts and subsequently delivered to the Earth. The formation ages of these samples range from 4.5 b.y. to 180 m.y. Collectively, these samples are called SNC meteorites after the major petrologic subdivisions: Shergottite, Nakhlite, Chassigny. The whole-rock Rb-Sr isochron for the shergottites is indistinguishable from the age of the solar system ~4.5 b.y. Because the Sm-Nd system contains two chronometers, it is possible to produce a concordia diagram, conceptually similar to that for the U-Pb system. Several shergottites define a time of differentiation of 4.53 b.y. on this Sm-Nd concordia. Therefore, it is clear that Mars differentiated very early. Additionally, the source regions of the shergottites and nakhlites are so depleted in radioactive heat-producing elements that producing young (< 1 b.y.) basalts becomes problematic.

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Crystallization Age of NWA 1460 Shergottite: Paradox Revisted

L.E. Nyquist, Johnson Space Center, Houston

We have determined the Rb-Sr age of basaltic shergottite NWA 1460 to be 312±3 Ma, and the Sm-Nd age to be 352±30 Ma. The initial Sr and Nd isotopic compositions of NWA 1460 suggest it is an earlier melting product of a Martian mantle source region similar to those of the lherzolitic shergottites and basaltic shergottite EETA79001, lithology B. The new ages of NWA 1460 and other recently analyzed Martian meteorites leads us to reexamine the paradox that most of the Martian meteorites appear to be younger from the majority of the Martian surface. This paradox continues to pose a challenge to determining a reliable Martian chronology.

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Evolution of the Early Atmospheres of Venus, Earth and Mars

David Catling, University of Washington, Seattle

Summary:

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Impact Constraints on Major Events in Early Mars History

Hebert Frey, Goddard Space Flight Center, Greenbelt, MD

MOLA data have revealed a large population of “Quasi-Circular Depressions” (QCDs) with little or no visible expression in image data. These likely buried impact basins have important implications for the age of the lowland crust, how that compares with original highland crust, and when and how the crustal dichotomy may have formed. The buried lowlands are of Early Noachian age, likely slightly younger than the buried highlands but older than the exposed (visible) highland surface. A depopulation of large visible basins at diameters 800 to 1300 km suggests some global scale event early in martian history, maybe related to the formation of the lowlands and/or the development of Tharsis. A suggested early disappearance of the global magnetic field can be placed within a temporal sequence of formation of the very largest impact basins. The global field appears to have disappeared at about the time the lowlands formed. It seems likely the topographic crustal dichotomy was produced very early in martian history by processes which operated very quickly. Thus there appears to have been a northern lowland throughout nearly all of martian history, predating the last of the really large impacts (Hellas, Argyre and Isidis) and their likely very significant environmental consequences.

Run Time: 23:57   Bit Rate: 73 kbps
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New Perspectives on Early Mars

Maria T. Zuber, Massachussetts Institute of Technology, Cambridge

Global data sets returned by the Mars Global Surveyor (MGS), Mars Odyssey, and Mars Express spacecraft and recent analyses of Martian meteorites suggest that most of the major geological events of Martian history occurred within the first billion years of solar system formation. This period was a time of heavy impact bombardment of the inner solar system, a process that strongly overprinted much of the Martian geological record from that time. Geophysical signatures nonetheless remain from that period in the Martian crust, and several geochemical tracers of early events are found in Martian meteorites. Collectively, these observations provide insight into the earliest era in Martian history when the conditions favoring life were best satisfied.

Run Time: 24:44   Bit Rate: 41 kbps
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Magma Ocean Cumulate Overturn: Generation of an Early Magnetic Field

Linda T. Elkins-Tanton, Brown University

Dynamical models of Martian differentiation and early evolution need to be consistent with several major attributes of Mars believed to have developed before 4.0 Ga: differentiation of mantle source regions into isotopically distinct reservoirs; development of an early, brief, strong magnetic field; and the formation of an early crust to record that field. Significant and perhaps complete melting of the large terrestrial planets is expected due to the conversion of kinetic energy to heat during accretion of planetesimals, and to the potential energy release of core formation. Previous results of Martian magma ocean investigations indicate that magma ocean crystallization and subsequent overturn on Mars could be fast and complete, and is consistent with magma source region differentiation and the development of an alumina-poor Martian mantle. The further results presented here demonstrate that magma ocean crystallization and overturn can produce a magnetic field of between 10 and 50 million years duration.

Run Time: 12:40   Bit Rate: 39 kbps
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Modeling the Effects of Impacts on Mars in 1-D

Teresa L. Segura, University of Colorado, Boulder and NASA Ames Research Center
O. Brian Toon, University of Colorado, Boulder
Anthony Colaprete, NASA Ames Research Center
Kevin Zahnle, NASA Ames Research Center

This work builds off the work done by Segura et al. (2002) in which we looked at the environmental effects of large (> 100 km) asteroid impacts on Mars. Our most recent results show that the effects of smaller impactors (those 30 - 100 km in diameter) are as important as the effects of the largest impactors. Our new model includes a hydrological cycle, the latent heating of cloud formation/evaporation, and the radiative effects of water clouds. We find that the combined effects of all impactors 50 km diameter and larger (in model runs where the radiative effects of clouds are excluded) could contribute to erosion totals of at least 20-70 meters when erosion due to precipitation and groundwater sapping are considered. If the Noachian erosion rates were 0.1-10 microns/yr for 500 million years, as estimated by some researchers, then the total erosion computed by this research falls within the ranges defined by these rates. However, we believe our calculated totals are minima, and when the radiative effects of water clouds are included, the erosion totals could be much larger, perhaps by a factor of 10 or more.

Run Time: 11:12   Bit Rate: 41 kbps
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The MER Mission and the Stratigraphic History of the Meridiani Planum

Steven Squyres, Cornell University

Summary: The landing site at Meridiani Planum was selected partly because coarse gray hematite was expected to be present on the basis of orbital data. Microscopic images of undisturbed surface soil show that one component is fine (~100 micron) sand. Mössbauer spectra of the sand show two ferrous doublets (one of them due to olivine), a ferric doublet, and a weak magnetic sextet. APXS and Mini-TES data on this sand are consistent with a composition dominated by basalt. Another component of the soil consists of coarse (several mm) granules. These range in shape from subangular to rounded to remarkably spherical. It is finely laminated, with typical layer thicknesses of only a few mm. The texture of the outcrops as viewed in microscopic images suggests that it is fine-grained, with well-expressed structure that is revealed by varying degrees of mechanical abrasion of layers of varying induration. APXS results on this fine-grained matrix suggest an unusual composition, including sulfur concentrations significantly higher than any observed elsewhere on Mars. This talk emphasizes the results obtained after the first 90 sols. At the time of this writing, the Opportunity rover has entered Endurance crater, a crater 150 m in diameter, 750 m from the landing area. Endurance is a crater of spectacular topography. Sedimentary structures dominate its upper rim. Because the mechanism responsible for the observed banding is not perfectly understood, RAT holes were drilled frequently as Opportunity descended into the crater.

Run Time: 34:24   Bit Rate: 46 kbps
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"Blueberries": A Summary of Hematite Concretions Found at the Opportunity Landing Site

Wendy Calvin, University of Nevada, Reno, et al.

The thermal infrared spectral signature of bulk, grey hematite was the chemical “beacon” that focused the selection of Meridiani Planum as the landing site for MER-B, Opportunity. Although processes from anhydrous volcanic to aqueous sedimentary were possible for the origin of the bulk hematite, aqueous processes, and in particular deposition in basins, were preferred. Orbital data suggesting more bound water in accessory minerals at the hematite sites also supported this interpretation. After landing January 24, 2004, the Mini-TES instrument on Opportunity rapidly confirmed the thermal spectral signature of bulk hematite in soils on the plains surrounding Eagle crater and unevenly distributed within the crater. Approach and observations of the outcrop within Eagle crater soon uncovered unusual millimeter sized spherical grains in abundance surrounding the outcrop and Microscopic Imager (MI) showed these grains eroding from within these rocks. They were dubbed “blueberries” by the team due to their spherical nature and their grey or blue appearance compared to their surroundings in various color composites of Pancam images. This term was also easier on the tongue in early science discussions than spherules or spherical grains, and avoided connotations of origin as would be implied by lapilli or oolites.

Run Time: 15:58   Bit Rate: 47 kbps
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Surficial Geology of the Sprit Rover Traverse in Gusev Crater: Dry and Desiccating Since the Hesperian

M.P. Golombek, Jet Propulsion Laboratory, Caltech
Athena Science Team

The Spirit rover landed successfully in a low albedo portion of Gusev crater at 14.5692°S, 175.4729°E on January 3, 2004 and has traversed about 3.5 km over 180 sols through cratered plains to Bonneville crater and the Columbia Hills. Gusev, a 160 km diameter Noachian crater that lies at the terminus of the 900 km long Ma’adim Vallis, was selected as a landing site to search for evidence of previous liquid water flow and/or ponding. Although no clear evidence of fluvial or lacustrine activity has been identified in the cratered plains (excepting rocks in the Columbia Hills), their surficial geology strongly limits any warmer and/or wetter period of Mars history (e.g., observed at Meridiani Planum) to be pre-Late Hesperian. This paper will review the surficial geology of Gusev crater as observed along the traverse by Spirit with special reference to the derived gradation history that strongly argues for a dry and desiccating environment since the Late Hesperian.

Run Time: 19:39   Bit Rate: 71 kbps
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Tuesday, October 12, 2004

Exploring for Fossil Biomarkers

Linda Jahnke, NASA Astrobiology Institute, Ames Research Center

Summary: The microbial communities that characterize modern hydrothermal ecosystems serve as modern analogs to those thought to have dominated early environments on Earth and possibly Mars. We are interested in the processes involved in the deposition and/or degradation of organic material in moderately thermal, silicifying microbial mats, particularly as this relates to the potential for preservation of some biomarker components known to be more highly resistant to microbial degradation. Several excellent biomarker molecules are associated with the cyanobacteria that dominate these mats, particularly the 2-methylbacteriohopanepolyols (2-MeBHP). These compounds are ubiquitous on Earth and are not easily degraded in nature, a fact documented by their detection in ancient Earth rocks dating back as far as 2,700 Ma. In our current studies of the early diagenetic effects on lipid biomarkers, we have found a significant correlation between silicification and the preservation of these hopanoid compounds. Our results suggest that silicification can provide a mechanism for hopanoid survival during early diagenetic alteration.

Run Time: 27:57   Bit Rate: 35 kbps
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Life Detection on the Early Earth

Bruce Runnegar, NASA Astrobiology Institute, Ames Research Center

Finding evidence for first the existence, and then the nature of life on the early Earth or early Mars requires both the recognition of subtle biosignatures and the elimination of false positives. The history of the search for fossils in increasingly older Precambrian strata illustrates these difficulties very clearly, and new observational and theoretical approaches are both needed and being developed. At the microscopic level of investigation, three-dimensional morphological characterization coupled with in situ chemical (isotopic, elemental, structural) analysis is the desirable first step. Geological context is paramount, as has been demonstrated by the controversies over AH84001, the Greenland graphites, and the Apex chert “microfossils”. At larger scales, the nature of sedimentary bedforms and the structures they display becomes crucial, and here the methods of condensed matter physics prove most useful in discriminating between biological and non-biological constructions. Ultimately, a combination of geochemical, morphological, and contextural evidence may be required for certain life detection on the early Earth or elsewhere.

Run Time: 28:53   Bit Rate: 48 kbps
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Wednesday, October 13, 2004

Thursday, October 14, 2004

The Early Climate of Mars: Warm, Cold or Forever Unknowable? Ambiquities Resulting from Impact Seismicity and Hydrothermal Activity

S.M. Clifford, Lunar and Planetary Institute, Houston

The resemblance of the Martian valley networks to terrestrial runoff channels, and their almost exclusive occurrence in the planet’s ancient cratered terrain, has suggested to some that the networks are the relics of a substantially warmer and wetter greenhouse climate that may have existed throughout much of the Noachian. Additional support for this possibility is provided by the apparent deficit of craters with diameters <30 km, and the poor preservation state of most large craters, within the intercrater plains. These observations have been cited as possible evidence of a dense early atmosphere that both warmed the early climate and accelerated the rates of fluvial and eolian erosion. Skeptics of the warm early Mars hypothesis have noted the theoretical difficulty of creating and sustaining an atmospheric greenhouse sufficient to raise surface temperatures above 273 K – particularly in light of the early Sun’s expected ~25% lower luminosity.

Run Time: 25:41   Bit Rate: 46 kbps
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Life in Ice on Mars

C.P. McKay, NASA Ames Research Center, Mt. View, CA

Summary: Although current evidence suggests that the surface of Mars is inimical to life as we know it, there remain plausible scenarios for extant microbial life on Mars, but only of very modest plausibility. It's commonly said that life is abundant on Earth, but it's not true. There are large swaths of area on Earth where life has been extinct for significant periods of time. The surface of Mars today is far more inhospitable to life than any of these areas on Earth. It is cold, dry, and chemically oxidizing and is exposed to an intense flux of solar ultraviolet radiation. Temperature is of interest, not only because of its controlling influence on metabolic rates but also because of its influence on the stability of liquid water. Liquid water is essential for life. All known terrestrial life is based on aqueous chemistry. That's not theory. It's merely an observation, but given our current state of knowledge in chemistry and biology, it is hard to imagine the existence of life independent of liquid water.

Run Time: 27:56   Bit Rate: 45 kbps
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Potential for Early Life Hosted in Basaltic Glass on a Wet Mars

Neil R. Banerjee, University of Alberta, University of Bergen, Norway
Karlis Muehlenbachs, University of Alberta
Harald Furnes, University of California
Hubert Staudigel, University of California
Maarten de Wit, University of Cape Town, South Africa

Recent evidence for the presence of liquid water and the formation of palagonite during the evolution of Mars has sparked considerable interest in determining if life could have existed early in the planet’s history. Previous indications of life in Martian meteorite ALH84001 have been criticized and new studies have been looking for terrestrial proxies for life on Mars. Evidence for early life on Earth has also proven to be controversial. We have recently discovered indicators of early life in the formerly glassy rims of ~3500 million year- old basaltic pillow lavas. Ancient volcanic glass represents a previously unexplored setting in the search for early life on Earth. The cratered surface of Mars likely hosts countless glassy basaltic impact breccias that may have been submerged in water for extended periods of time. Such rocks represent a viable habitat for early life on Mars.

Run Time: 10:59   Bit Rate: 63 kbps
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Friday, October 15, 2004

Targeting Sites for Furture Astrobiological Missions to Mars

Jack Farmer, Arizona State University

In defining a site-selection strategy to explore for a martian fossil record, a key concept is contemporaneous chemical precipitation, or mineralization. This process entombs microorganisms, stabilizes morphological information and protects biosignatures during subsequent diagenetic changes. On Earth, geological environments where microorganisms are often preserved in this way include: 1) mineralizing spring systems (subaerial, subaqueous, and shallow subsurface hydrothermal systems, and cold springs of alkaline lakes), 2) saline/alkaline environments of arid marine shorelines (sabkhas), or terminal (evaporative) lake basins, 3) duricrusts and subsoil hard-pan environments formed by the selective leaching and re-precipitation of minerals within soil profiles, and 4) periglacial environments ground ice or permafrost (frozen soils) have captured and cryopreserved microorganisms and associated organic materials. Successful implementation of a strategy for Mars exopaleontology will depend on targeting the most favorable landing sites for in situ robotic exploration and sample return.

Run Time: 24:00   Bit Rate: 48 kbps
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Mars Exploration: What's Next?

Dan McCleese, Jet Propulsion Laboratory

Summary: The community consensus is that we are in a tremendously exciting time in exploring Mars. The MER mission has achieved some spectacular results. The remote sensing by the MEX, MGS, and Odyssey spacecraft is continuing to shed new light on science questions and to raise new questions. The upcoming slate of missions that are in advanced states of planning and implementation -- MRO, Phoenix, and MSL -- and the missions to follow that are in earlier planning are exciting science missions that address significant questions. The renewed emphasis on the combination of exploration and science is creating new opportunities and a sense of real advance. The MER mission demonstrated unequivocally the importance and value of mobility in carrying out science operations on the martian surface. Without rover mobility, for example, the Opportunity spacecraft would have sat tantalizingly close to Opportunity Ledge, unable to investigate it close up and in detail and thereby make the discoveries that it has.

Run Time: 25:17   Bit Rate: 32 kbps
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