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NASA NTRS2001

Technologies for Icy Bodies Access

Recent events in planetary exploration have profoundly changed the way both space scientists and the public regard the solar system and our place in it. These events include the Galileo data suggesting subsurface oceans in the Jovian system, ever stronger suggestions of near-surface water on Mars, as well as the complex structure observed for the Mars polar caps. And, of course, interest in icy cometary bodies is as old as humankind. Finally, the Mars north polar cap may conceivably cover and protect an ancient ocean floor, an obvious candidate ancient or extant habitat. In short, our interest in searching for life embraced early on the search for liquid water, and that has led us to an additional appreciation for water ice as both a commonplace partner with liquid water and as an issue to be addressed in the exploration of a host of interesting sites. In general, the spectrum of specialized technology for space exploration has not yet been broadened to include the requirements brought about by exploration of icy sites. We argue that technologies for access, operations, and science in icy solar system sites must be examined and their prioritized development initiated in order to successfully plan missions to these compelling sites over the next two decades. Additional information is contained in the original extended abstract.

Carsey, F. D.↗

NASA NTRS2001

Changes in the Earth's UV Reflectivity (1979 to 1992)

Measurements of the Earth,s 380 nm UV reflectivity combine the effects of surface reflectivity, aerosols, haze, cloud optical thickness, and the fraction of the scene covered by clouds. Since the 380 nm surface reflectivity is low (2 to 8%) over most surfaces, water and land, the observed reflectivity changes are mostly caused by changes in the amount of snow/ice, cloudiness and aerosols. Time-series analysis of TOMS reflectivity over the period from 1979 to 1992 shows that there were no significant changes in annually-averaged zonal-average reflectivity at latitudes within 60 degrees S to 60 degrees N, even though there were changes at higher latitudes (e.g., 3% per decade, in reflectivity units, between 60 degrees N and 70 degrees N). When the effects of the 11-year solar cycle and ENSO (El Nino Southern Oscillation) are removed from the data, statistically significant reflectivity changes are observed poleward of both 40 degrees S and 40 degrees N. The solar-cycle results suggest a possible Sun-weather relationship.

Hermana, J. R.↗

NASA NTRS1994

Environmental Perturbations Caused by the Impacts of Comets and Asteroids on Earth

The extinction mechanisms proposed at the Cretaceous-Tertiary geological boundary are reviewed and related to the impact of asteroids or comets in general. For impact energies below 10(exp 4) Megatons (less than 6 x 10(exp 4) years; asteroid diameter less than 650 m), blast, earthquake, and fire may destroy local areas up to 10(exp 5) square m. Tidal waves could flood a kilometer inland over entire ocean basins. The energy range from 105 to 106 Megatons (less than 2 x 10(exp 6) years; asteroid diameter less than 3 km) is transitional. Dust lifted, sulfur released from within impacting asteroids, and soot from fires started by comets can produce climatologically significant optical depths of 10. At energies beyond 10(exp 7) Megatons, blast and earthquake damage is regional (10(exp 6) square cm). Tsunami cresting to 100 m and flooding 20 km inland will sweep the coastal zones of the world's oceans. Fires will be set globally. Light levels may drop so low from the smoke, dust and sulfate that vision is not possible. At energies approaching 10(exp 9) Megatons the ocean surface waters may be acidified by sulfur. The combination of these effects would be devastating.

Toon, Owen B.↗

NASA NTRS2001

Validation of Ocean Color Satellite Data Products in Under Sampled Marine Areas

The planktonic marine cyanobacterium, Trichodesmium sp., is broadly distributed throughout the oligotrophic marine tropical and sub-tropical oceans. Trichodesmium, which typically occurs in macroscopic bundles or colonies, is noteworthy for its ability to form large surface aggregations and to fix dinitrogen gas. The latter is important because primary production supported by N2 fixation can result in a net export of carbon from the surface waters to deep ocean and may therefore play a significant role in the global carbon cycle. However, information on the distribution and density of Trichodesmium from shipboard measurements through the oligotrophic oceans is very sparse. Such estimates are required to quantitatively estimate total global rates of N2 fixation. As a result current global rate estimates are highly uncertain. Thus in order to understand the broader biogeochemical importance of Trichodesmium and N2 fixation in the oceans, we need better methods to estimate the global temporal and spatial variability of this organism. One approach that holds great promise is satellite remote sensing. Satellite ocean color sensors are ideal instruments for estimating global phytoplankton biomass, especially that due to episodic blooms, because they provide relatively high frequency synoptic information over large areas. Trichodesmium has a combination of specific ultrastructural and biochemical features that lend themselves to identification of this organism by remote sensing. Specifically, these features are high backscatter due to the presence of gas vesicles, and absorption and fluorescence of phycoerythrin. The resulting optical signature is relatively unique and should be detectable with satellite ocean color sensors such as the Sea-Viewing Wide Field-of-view Sensor (SeaWiFS).

Subramaniam, Ajit↗

NASA NTRS1995

A Strategy for Mars Exopaleontology

There is compelling geological evidence that the climate of early Mars was much more Earth-like, with a denser atmosphere and abundant surface water. Given that life developed on the Earth very quickly (between 4.2 and 3.5 Ga), it is quite plausible that life may have also developed on Mars during this early clement period. If Martian life developed, it is likely to have left behind a fossil record. Thus, an important focus for upcoming Mars missions is to explore for an ancient biosphere. This presents a set of goals and problems that are quite distinct from Exobiology. I call this new activity "Exopaleontology", whose core principles derive from studies of the Precambrian fossil record on Earth, biosedimentology and microbial fossilization. Such studies reveal that the most important factor favoring the long-term preservation of microbial fossils is rapid entombment of microorganisms by fine-grained, stable mineral phases such as silica, phosphate, carbonate and metal sulfides. Terrestrial environments where such aqueous mineral phases frequently entomb and preserve microorganisms include subaerial and subaqueous springs and shallow hydrothermal systems, evaporitic alkaline lakes, "hardpan" soils (e.g. calcretes, silcretes, ferracretes), and frozen soils or ground ice. With the exception of ice, which has a short crustal residence time, such deposits am known to retain a record of terrestrial life for billions of years. Current activities seek to refine and apply this strategy to the Mars Global Surveyor missions and beyond. Ongoing studies of microbial fossilization in each of the target environments identified above are aimed at improving our understanding of how biological information is incorporated into aqueous mineral deposits and preserved. Viking data is being used to target sites for high resolution orbital imaging and spectroscopy during upcoming Mars missions. Such data will provide a basis for selecting sites for future landed missions and eventually, sample return.

Farmer, Jack D.↗

NASA NTRS1998

Influence of Mesoscale Eddies on New Production in the Sargasso Sea

It is problematic that geochemical estimates of new production - that fraction of total primary production in surface waters fueled by externally supplied nutrients - in oligotrophic waters of the open ocean surpass that which can be sustained by the traditionally accepted mechanisms of nutrient supply. In the case of the Sargasso Sea, for example, these mechanisms account for less than half of the annual nutrient requirement indicated by new production estimates based on three independent transient-tracer techniques. Specifically, approximately one-quarter to one-third of the annual nutrient requirement can be supplied by entrainment into the mixed layer during wintertime convection, with minor contributions from mixing in the thermocline and wind-driven transport (the potentially important role of nitrogen fixation - for which estimates vary by an order of magnitude in this region - is excluded from this budget). Here we present four lines of evidence - eddy-resolving model simulations, high-resolution observations from moored instrumentation, shipboard surveys, and satellite data - which suggest that the vertical flux of nutrients induced by the dynamics of mesoscale eddies is sufficient to balance the nutrient budget in the Sargasso Sea. Additional information is contained in the original extended abstract.

McGillicuddy , Dennis J., Jr.↗

NASA NTRS2002

An Overview of the Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) Data Products Status and Availability for Environmental Applications and Global Change Studies

The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System (EOS) Terra Mission began to produce data in February 2000. The Terra MODIS is in a sun-synchronous orbit going north to south in the daylight portion of the orbit crossing the equator at about 1030 hours local time. The spacecraft, instrument, and data systems are performing well and are producing a wide variety of data products useful for scientific and applications studies in relatively consistent fashion extending from November 2000 to the present. Within the approximately 40 MODIS data products, several are new and represent powerful and exciting capabilities such the ability to provide observations over the globe of fire occurrences, microphysical properties of clouds and sun-stimulated fluorescence from phytoplankton in the surface waters of the ocean. The remainder of the MODIS products exceed or, at a minimum, match the capabilities of products from heritage sensors such as, for example, the Advanced Very High Resolution Radiometer (AVHRR). Efforts are underway to provide data sets for the greater Earth science community and to improve access to these products at the various Distributed Active Archive Centers (DAAC's) or through Direct Broadcast (DB) stations. The MODIS instrument on the EOS Aqua mission should also be expected to be in orbit and functioning in the Spring of 2002. The Aqua spacecraft will operate in a sun-synchronous orbit going south to north in the daylight portion of the orbit crossing the equator at approximately 1330 hours local time. Subsequently the Aqua MODIS observations will substantially add to the capabilities of the Terra MODIS for environmental applications and global change studies.

Salomonson, Vincent V.↗

NASA NTRS2002

Software Construction and Analysis Tools for Future Space Missions

NASA and its international partners will increasingly depend on software-based systems to implement advanced functions for future space missions, such as Martian rovers that autonomously navigate long distances exploring geographic features formed by surface water early in the planet's history. The software-based functions for these missions will need to be robust and highly reliable, raising significant challenges in the context of recent Mars mission failures attributed to software faults. After reviewing these challenges, this paper describes tools that have been developed at NASA Ames that could contribute to meeting these challenges; 1) Program synthesis tools based on automated inference that generate documentation for manual review and annotations for automated certification. 2) Model-checking tools for concurrent object-oriented software that achieve memorability through synergy with program abstraction and static analysis tools.

Lowry, Michael R.↗

NASA NTRS1998

Influence of Mesoscale Eddies on New Production in the Sargasso Sea

It is problematic that geochemical estimates of new production, that fraction of total primary production in surface waters fueled by externally supplied nutrients, in oligotrophic waters of the open ocean surpass that which can be sustained by the traditionally accepted mechanisms of nutrient supply. In the cam of the Sargasso Sea, for example, these mechanisms account for less than half of the annual nutrient requirement indicated by new production estimates based on three independent transient-tracer techniques. Specifically, approximately one-quarter to one-third of the annual nutrient requirement can be supplied by entrainment into the mixed layer during wintertime convection, with minor contributions from mixing in the thermocline and wind-driven transport (the potentially important role of nitrogen fixation- for which estimates vary by an order of magnitude in this region- is excluded from this budget). Here we present four lines of evidence-eddy-resolving model simulations, high-resolution observations from moored instrumentation, shipboard surveys and satellite data-which suggest that the vertical flux of nutrients induced by the dynamics of mesoscale eddies is sufficient to balance the nutrient budget in the Sargasso Sea.

McGillicuddy, D. J., Jr.↗

NASA NTRS2003

An Overview of the Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) Data Products and Availability for Environmental Applications and Global Change Studies

The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System (EOS) Terra Mission began to produce data in February 2000. The Terra MODIS is in a sun-synchronous orbit going north to south in the daylight portion of the orbit crossing the equator at about 1030 hours local time. The spacecraft, instrument, and data systems are performing well and are producing a wide variety of data products useful for scientific and applications studies in relatively consistent fashion extending from November 2000 to the present. Within the approximately 40 MODIS data products, several are new and represent powerful and exciting capabilities such the ability to provide observations over the globe of fire occurrences, microphysical properties of clouds and sun-stimulated fluorescence from phytoplankton in the surface waters of the ocean. The remainder of the MODIS products exceeds or, at a minimum, matches the capabilities of products from heritage sensors such as, for example, the Advanced Very High Resolution Radiometer (AVHRR). Efforts are underway to provide data sets for the greater Earth science community and to improve access to these products at the various Distributed Active Archive Centers (DAACs) or through Direct Broadcast (DB) stations. The EOS Aqua mission was launched successfully May 4,2002 with another MODIS on it. The Aqua spacecraft operates in a sun-synchronous orbit going south to north in the daylight portion of the orbit crossing the equator at approximately 1330 hours local time. Subsequently the Aqua MODIS observations will substantially add to the capabilities of the Terra MODIS for environmental applications and global change studies.

Salomonson, V. V.↗

NASA NTRS2003

Spherule Beds 3.47-3.24 Billion Years Old in the Barberton Greenstone Belt, South Africa: A Record of Large Meteorite Impacts and Their Influence on Early Crustal and Biological Evolution

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approx. 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.

Lowe, Donald R.↗

NASA NTRS2003

Icelandic Pseudocraters as Analogs to some Volcanic Cones on Mars

Pseudocraters are rootless vents formed by the interaction of lava flows with surface or near-surface water. This interaction can produce mild explosions and the accumulation of scoria and spatter into small constructs. Pseudocraters in several localities in Iceland were examined in the field and compared to similar appearing features observed on Mars. The Icelandic pseudocrater cones in this study range in size from 6 to 70 m in diameter, have summit craters which range from 2 to 28 m in diameter (many cones lack craters entirely), and have flanks that am either concave- up or convex-up. The size and spacing of Icelandic pseudo-craters might be a function of the availability of water, in which larger, closely spaced features result from efficient lava-water interaction, as suggested by the environments in which the features formed. Possible Martian pseudocrater cones in Amamnis Planitia range in diameter from 30 to 180 m and have craters 12 to 80 m in diameter. A numerical model for volcanic explosions was adapted to study the formation of pseudocraters under terrestrial and Martian conditions. The results suggest that explosions forming Martian cones require significantly less water (calculated masses am less by a factor of 4 to 16) than those forming Icelandic pseudokers, despite their larger sizes, This is attributed to the low gravity and atmospheric pressure in the Mars environment and is consistent with the likely lower abundance of water, which might be present as interstitial ice at shallow depths in the regolith. Locations of potential pseudocraters on Mars at latitudes as low as approximately 8 degrees N, imply the presence of crustal ice stores at the time of their formation.

Greeley, Ronald↗

NASA NTRS2003

New Total Ozone Algorithm for Application to the Total Ozone Mapping Spectrometer

The Total Ozone Mapping Spectrometer (TOMS) series comprises four instruments providing a total of 25 years of daily global stratospheric ozone data over the sunlit portion of the Earth. A new retrieval algorithm has been developed for TOMS, designated Version 8. The algorithm is based on differential absorption across a pair of wavelength channels chosen close together to minimize the impact of wavelength dependent forward modeling errors. Version 8 enhancements include correction for the presence of tropospheric aerosols and sun glint from water surfaces, a better treatment of variability due to tropospheric ozone and temperature dependence, and an improved forward model, particularly in regions of persistent snow and ice. Among other things, the Version 8 enhancements have reduced latitudinal dependence seen previously in TOMS - Dobson comparisons, predominantly in the Southern Hemisphere's summer, when the tropospheric ozone, temperature, and snow/ice corrections are additive. The basic components of the algorithm and its impact on derived total ozone will be discussed.

Wellemeyer, C.↗

NASA NTRS2000

Multispectral In-situ Measurements of Organic Matter and Chlorophyll Fluorescence in Seawater: Documenting the Intrusion of the Mississippi River Plume in the West Florida Shelf

We performed multispectral in-situ fluorescence measurement of colored dissolved organic matter and chlorophyll in surface water of the West Florida Shelf using West Labs Spectral absorption and Fluorescence Instrument (SAFIre). Continuous measurements underway allowed us to simultaneously map the dispersion of riverine organic material and chlorophyll on the shelf. By using two fluorescence emission ratios we were able to differentiate between riverine and marine CDOM. Our data also showed unusually high concentrations of CDOM offshore. These were attributed to an intrusion of the Mississippi River Plume. We performed limited comparisons between in-situ chlorophyll concentrations measured with SAFIre and chlorophyll values obtained from SeaWiFS satellite data using OC4 and MODIS algorithm. Our results show that, although both algorithms overestimated chlorophyll, MODIS performed better than OC4, particularly in areas with high CDOM concentrations. Analysis of the relationship between chlorophyll and CDOM concentrations within the study area showed regional variability causes by differences in river source.

DelCastillo, Carlos E.↗

NASA NTRS2003

The NASA Earth Observing System (EOS) Terra and Aqua Mission Moderate Resolution Imaging Spectroradiometer (MODIS: Science and Applications

The Moderate Resolution Imaging Spectroradiometer (MODIS) on the Earth Observing System (EOS) Terra Mission began to produce data in February 2000. The EOS Aqua mission was launched successfully May 4,2002 with another MODIS on it and "first light" observations occurred on June 24,2002. The Terra MODIS is in a sun-synchronous orbit going north to south in the daylight portion of the orbit crossing the equator at about 1030 hours local time. The Aqua spacecraft operates in a sun-synchronous orbit going south to north in the daylight portion of the orbit crossing the equator at approximately 1330 hours local time. The spacecraft, instrument, and data systems for both MODIS instruments are performing well and are producing a wide variety of data products useful for scientific and applications studies in relatively consistent fashion extending from November 2000 to the present. Within the approximately 40 MODIS data products, several are new and represent powerful and exciting capabilities such the ability to provide observations over the globe of fire occurrences, microphysical properties of clouds and sun-stimulated fluorescence from phytoplankton in the surface waters of the ocean. The remainder of the MODIS products exceeds or, at a minimum, matches the capabilities of products from heritage sensors such as, for example, the Advanced Very High Resolution Radiometer (AVHRR). Efforts are underway to provide data sets for the greater Earth science community and to improve access to these products at the various Distributed Active Archive Centers (DAAC's) or through Direct Broadcast (DB) stations.

Salomnson, Vincent V.↗

NASA NTRS2003

Black Carbon in Estuarine (Coastal) High-molecular-weight Dissolved Organic Matter

Dissolved organic matter (DOM) in the ocean constitutes one of the largest pools of organic carbon in the biosphere, yet much of its composition is uncharacterized. Observations of black carbon (BC) particles (by-products of fossil fuel combustion and biomass burning) in the atmosphere, ice, rivers, soils and marine sediments suggest that this material is ubiquitous, yet the contribution of BC to the ocean s DOM pool remains unknown. Analysis of high-molecular-weight DOM isolated from surface waters of two estuaries in the northwest Atlantic Ocean finds that BC is a significant component of DOM, suggesting that river-estuary systems are important exporters of BC to the ocean through DOM. We show that BC comprises 4-7% of the dissolved organic carbon (DOC) at coastal ocean sites, which supports the hypothesis that the DOC pool is the intermediate reservoir in which BC ages prior to sedimentary deposition. Flux calculations suggest that BC could be as important as vascular plant-derived lignin in terms of carbon inputs to the ocean. Production of BC sequesters fossil fuel- and biomass-derived carbon into a refractory carbon pool. Hence, BC may represent a significant sink for carbon to the ocean.

Mannino, Antonio↗

NASA NTRS2004

Search for Evaporite Minerals in Flaugergues Basin, Mars

Studies of Martian surface geomorphology and detection of near-surface water ice by the Mars Odyssey gamma ray spectrometer suggest that Mars may have had a water-rich past. While 2 to 5 wt.% of carbonate has been detected in the Martian dust [1,2], no spectral evidence for significant deposits of carbonates or sulfates has been found to date. Most investigations into Mars aqueous mineralogy have been global in scope with only a few regional studies (e.g., [3]). We are searching for localized deposits in putative lacustrine basins utilizing a basin flow model to identify basins with large drainage areas. Such basins are more likely to accumulate high concentrations of aqueous minerals than deep basins which drain only small regions.

Dalton, J. B.↗

NASA NTRS2003

Low-Temperature, Aqueous Alteration of Soil in Wright Valley, Antarctica, Compared with Aqueous Alteration on Mars

The Dry Valleys of Antarctica are possibly one of the best analogs on Earth of the environment at the surface of Mars. Many types of research have been focused on the Dry Valleys, partly because of the potential application to Mars, and also because of the importance of the Dry Valleys in understanding the characteristics and development of terrestrial polar deserts. In 1983, we published a detailed study of weathering products and soil chemistry in a soil pit at Prospect Mesa, Wright Valley, as a possible analog to Mars. Much more is now known about Mars, so we are re-examining that earlier work and comparing it with newer martian data. The Mars information most pertinent to this work includes (A) the strong evidence for recent aqueous activity on Mars, along with more recent evidence for present-day, near-surface water ice on Mars; and (B) the identification of meteorites from Mars and the subsequent, definitive proof that low temperature, aqueous weathering has occurred in these meteorites prior to their ejection from Mars.

Wentworth, S. J.↗