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At least 613 records · Page 34

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NASA NTRS1986

Search for volatiles in the surface of icy satellites

It is proposed to measure the reflectance spectra of the icy satellites of Jupiter, Saturn and Uranus in the spectral region 1.8 to 2.4 micrometers. These observations use the new Cooled Grating Array Spectrometer using a 32-element InSb photodiode array detector and produce spectra of higher resolution and precision than any data yet obtained; the ultimate scientific objective is to search for the signatures of methane clathrate, ammonium hydroxide or carbon monoxide clathrate (compounds predicted to exist on icy surfaces in the outer solar system by several theories of formation of these bodies) in the region of the spectrum where water ice has a relative maximum in reflectance. At the very least, these data will allow upper limits to be placed on the amount of these chemical species that can be present. The specific targets is Europa, Ganymede, Enceladus, Ariel and Titania, bodies that have the highest probability of having some or all of these volatiles on their surface according to current formation models.

Brown, R. H.↗

NASA NTRS1988

Volatiles on Mars

The long-term evolution of both the atmosphere and the surface of Mars can be understood by examining the history of volatiles in the Mars atmosphere, their non-atmospheric reservoirs, and the processes of exchange between the two. Clearly, the present state of both the surface and the atmosphere can only be seen, so that any inferences about the evolution of the climate system are just that, inferences. The processes which control the atmosphere and surface on a seasonal basis, however, are the same processes which can act on longer timescales; only the specific solar and atmospheric forcing will differ. Once the ability of each process to affect the seasonal behavior is understood, the long-timescale forcing may be applied to the various processes in order to clearly identify the ability of the processes to act over the entire history of Mars. The areas of surface-atmospheric interaction of Mars are addressed in the ongoing research. The climate system on Mars is controlled by processes involving the exchange between the surface and atmosphere, so it is important to understand the current behavior of those processes. This is especially so in light of the current interest in understanding Mars; the upcoming Mars Observer mission, and the potential for a future sample-return or human-exploration mission will focus emphasis on this area of Mars science.

Jakosky, Bruce M.↗

NASA NTRS1987

Spatial resolution and the geologic interpretation of Martian morphology - Implications for subsurface volatiles

Viking Orbiter images of the Acheron Fossae on Mars are presented and analyzed, with an emphasis on the impact of image resolution on the interpretation. High-resolution (less than 10 m/pixel) images reveal small mounds which can be interpreted as aeolian dunes, but these features are not evident on images with resolution of 50 m/pixel or greater. Also reported are the results of a visual inspection of 527 usable high-resolution images: it is found that all of the morphological features identified can arise in the absence of subsurface volatiles.

Zimbelman, James R.↗

NASA NTRS1987

Mineralogical studies of sulfide samples and volatile concentrations of basalt glasses from the southern Juan de Fuca Ridge

Sulfide samples obtained from Alvin dives on the southern Juan de Fuca Ridge were examined, showing the presence of two previously undiscovered minerals, both formed at low temperatures. The first detection of lizardite, starkeyite, and anatase in such an environment is also reported. Sulfide geothermometry involving the Cu-Fe-S system shows a vent temperature of less than 328 C for one sample. Ice-melting temperatures on inclusions from this sample are about -2.8 C, and fluid inclusion studies on crystals near this sample show pressure-corrected homogenization temperatures of 268 and 285 C. Volatile concentrations from vesicle-free basalt glass from the vent field are found to be about 0.0013 wt pct CO2 and 0.16 wt pct H2O.

Brett, Robin↗

NASA NTRS1987

Volatile inventory of Mars-2: Primordial sources and fractionating processes

The total volatile inventory of Mars has been modeled using meteoritic and presumed primordial abundances in the early solar system. Evidence is presented which indicates that the elemental abundances of the noble gases on Earth and Mars are similar, and their ratios are comparable to those in average carbonaceous chondrites with the exception of xenon and krypton. In order to account for presently observed variations in gas abundances, two primordial sources were used. One was the solar composition similar to the solar wind, and the other of carbonaceous grains that were the source for trace exotic components. For Mars, a model in which the early, high solar EUV flux with continued hydrogen production by differentiation results in mass fractionation of the primordial atmosphere, early depletion of xenon, and later depletion of gases lighter than krypton. The result is that the primordial Mars water inventory may have been on the order of 20 to 30 km if spread over the planet.

Pepin, R. O.↗

NASA NTRS1987

Volatilization-devolatilization reactions

Experiments that explore chemical and physical aspects of volatilization reactions that require the microgravity and low pressure in or near the projected Space Station are proposed.

Gilbert, M. C.↗

NASA NTRS1987

Volatilization-fractionation of silicates related to chondrite composition

The compositions of chondritic meteorites are linked to the solar composition. It is believed that the chemistry of the (generally) drop-shaped chondrules which comprise a large portion of these meteorites may present valuable clues to their formation and, ultimately, to the early conditions and processes of the planets. The purpose of this experiment is to determine the nature of volatilization-fractionation of silicate (and related metallic) compositions related to chondrite composition.

Walter, L. S.↗

NASA NTRS1988

Sampling the ancient volatile-rich areas of Mars

Viking images clearly show areas with a high density of fluidized craters that also display a significant number of wrinkle ridges. Fluidized crater ejecta morphology may indicate that the target material was rich in volatiles at the time of the impact. Therefore, these areas are of the utmost importance in deciphering both the Martian tectonic evolution and the amount of subsurface water, at times when more favorable conditions for life to evolve did exist on Mars. Although a large number of extensional features are associated with Tharsis and Elysium geologic activity, the planet-wide distribution of ridges suggests that Mars' tectonic history is far more complex than the Tharsis-dominated scenario indicates. Like on the Moon and Mercury, ridges on Mars were formed under compressive stresses, probably as a result of thrust-fault mechanism, although surface expressions and direct causes vary. Martian ridges are most easily seen on smooth plains of volcanic origin, but the majority of the 16,000 mapped and classified compressive features are located in the old terrains, far beyond Tharsis influence.

Chicarro, A. F.↗

NASA NTRS1988

ALH85085 - A unique volatile-poor carbonaceous chondrite with possible implications for nebular fractionation processes

The characteristics and possible origin of the chondrite ALH85085 are discussed. It is found that the metal silicate, and sulfide compositions of ALH85085 are similar to those in CM-CO and Al Rais-Renazzo chondrites. High siderophile abundances and volatile depletion are observed. It is found that ALH85085 agglomerated when temperatures in the nebula were near 1000 K, in the same region where Renazzo, Al Rais, and the CI chondrites formed. It is suggested that ALH85085 was annealed and lightly shocked after agglomeration. C1 and other clasts were subsequently incorporated during late-stage brecciation.

Grossman, Jeffrey N.↗

NASA NTRS1988

Distribution of volatile organic chemicals in outdoor and indoor air

The EPA volatile organic chemistry (VOC) national ambient data base (Shah, 1988) is discussed. The 320 chemicals included in the VOC data base are listed. The methods used to obtain the data are reviewed and the availability, accessibility, and operation of the data base are examined. Tables of the daily outdoor concentrations for 66 chemicals and the daily indoor concentrations for 35 chemicals are presented.

Shah, Jitendra J.↗

NASA NTRS1989

Isidis basin - Site of ancient volatile-rich debris layer

The differentiation of the Martian Isidis impact basin's interior plains into hillocky terrains with isolated mounds arranged in arctuate chains, and ridged terrains with systems of parallel curvilinear ridges, is presently suggested to reflect the deposition and subsequent removal of a thick layer of material within the basin. The process of terrestrial ice-cover dissintegration, which yields such landforms as moraines, kames, and eskers, furnishes a possible analog to the Isidis features; Viking orbiter images show Martian ridges with similar characteristics, suggesting that the Isidis layer may have been only part of a more general deposition period that coincided with one of major outflow channel formation involving the release of subsurface volatiles.

Grizzaffi, Patricia↗

NASA NTRS1990

Mars atmospheric D/H - Consistent with polar volatile theory?

Current theories on the Martian water history are discussed on the basis of data for the D/H ratio in the Martian atmosphere (which was found to be enhanced by a factor of 6 + or - relative to the value on earth). In particular, the calculations of Yung et al. (1988), on the basis of their photochemical model, are found to be inconsistent with current theories for the evolution of the polar deposits on Mars. While the photochemical model predicts that about 95 percent of the Martian water has escaped over geologic time and the nonatmospheric reservoir is now only 02 m thick, the polar volatile theory suggest that polar deposits contain the equivalent of tens of meters of water, requiring a more rapid escape of H and D to space than predicted by the photochemical model to match the observed D/H ratio. The paper examines the behavior of the polar caps and the atmospheric water vapor over geologic time and the loss of H and D to space. It is concluded that, at present, it is premature to accept a specific history for water on Mars.

Jakosky, Bruce M.↗

NASA NTRS1989

Solar nebula chemistry - Implications for volatiles in the solar system

Current theoretical models of solar nebula chemistry which take into account the interplay between chemistry and dynamics are presented for the abundant reactive volatile elements including hydrogen, carbon, nitrogen, oxygen, and sulfur. Results of these models indicate that, in the solar nebula, the dominant carbon and nitrogen gases were CO and NO, whereas, in giant planet subnebulae, the dominant carbon and nitrogen gases were CH4 and NH3; in the solar nebula, the Fe metal grains catalyzed the formation of organic compounds from CO and H2 via the Fischer-Tropsch-type reaction. It was also found that, in solar nebula, bulk FeS formation was kinetically favorable, while FeO incorporation into silicates and bulk Fe3O4 formation were kinetically inhibited. Furthermore, clathrate formation was kinetically inhibited in the solar nebula, while it was kinetically favorable in giant planet subnebulae.

Fegley, Bruce, Jr.↗

NASA NTRS1990

Solar nebula origin for volatile gases in Halley's comet

The conditions for Comet Halley formation are presently considered in light of the application of physical and chemical processes in the solar nebula environments to the present data base on the composition of the comet's gases. Key molecular ratios are compared to solar nebula model predictions, and the nebular thermochemistry is quantified for a range of solar elemental compositions which correspond to varying water depletion states in the inner nebula. Assuming that inner nebula chemistry is catalyzed by reaction on grains, it is judged that the abundances of the volatile C species CH4, CO, and CO2 in Halley could have been supplied by the solar nebula.

Engel, Steffi↗

NASA NTRS1990

Scatterers in Triton's atmosphere - Implications for the seasonal volatile cycle

Nitrogen and methane ices on the surface of Triton, Neptune's largest satellite, are exchanged between the summer and winter hemispheres on a seasonal time scale. Images of the satellite's sky obtained by the Voyager 2 spacecraft show the presence of several types of scattering materials that provide insights into this seasonal cycle of volatiles. Discrete clouds, probably composed of N2 ice particles, arise in regions of active sublimation. They are found chiefly poloward of 30 deg S in the southern, summer hemisphere. Haze particles, probably made of hydrocarbon ices, are present above most, but not all places. Recent snowfall may have occurred at low southern latitudes in places where they are absent. The latent heat released in the formation of the discrete clouds may have a major impact on the thermal balance of the lower atmosphere. Triton may have been less red at the time of the Voyager flyby than 12 years earlier due to recent N2 snowfall at a wide range of latitudes.

Pollack, James B.↗

NASA NTRS1991

The evolution of volcanism, tectonics, and volatiles on Mars - An overview of recent progress

Significant results of the 'Mars: Evolution of Volcanism, Tectonics, and Volatiles' (MEVTV) project are presented. The data for the project are based on geological mapping from the Viking images, petrologic and chemical analyses of SNC meteorites, and both mapping and temporal grouping of major fault systems. The origin of the planet's crustal dichotomy is examined in detail, the kinematics and formation of wrinkle ridges are discussed, and some new theories are set forth. Because the SNC meteorites vary petrologically and isotopically, the sources of the parental Martian magma are heterogeneous. Transcurrent faulting coupled with the extensional strains that form Valles Marineris suggest early horizontal movement of lithospheric blocks. A theory which connects the formation of the crustal dichotomy to the Tharsis region associates the horizontal motions with plate tectonics that generated a new lithosphere.

Zimbelman, James R.↗

NASA NTRS1992

Condensation Of Volatile Contaminant In An Instrument

Report describes investigation of deposition of contaminant of cooled optical detectors in Wide-Field/Planetary Camera (WF/PC), an instrument in Hubble Space Telescope. To understand phenomenon, initially thought to be deposition of water from graphite/epoxy optical-bench material in instrument, researchers mounted several diagnostic instruments on access plate to monitor interior of WF/PC housing and optical bench. Temperature-controlled quartz-crystal microbalance (TQCM) measures adsorbed and desorbed volatile condensible material on surfaces in WF/PC.

Hansen, Patricia A.↗

NASA NTRS1991

Volatiles in the outer solar system

Telescopic data on asteroids, comets, planets, and planetary satellites are acquired and analyzed in the study of volatile ices and gases that occur on their surfaces and in their atmospheres. Infrared spectral studies of certain classes of asteroids for an analysis of their mineralogical and organic constituents are included.

Cruikshank, Dale P.↗