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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Possible sources of H2 to H2O enrichment at evaporation of parent chondritic material

One of the results obtained from thermodynamic simulation of recondensation of the source chondritic material is that at 1500-1800 K it's possible to form iron-rich olivine by reaction between enstatite, metallic iron and water vapor in the case of (H2O)/(H2) approximately equal to 0.1. This could be reached if the gas depletion in hydrogen is 200-300 times relative to solar abundance. To get this range of depletion one needs some source material more rich in hydrogen than the carbonaceous CI material which is the richest in volatiles among chondrites. In the case of recondensation at impact heating and evaporation of colliding planetesimals composed of CI material, we obtain insufficiently high value of (H2)/(H2O) ratio. In the present paper we consider some possible source materials and physical conditions necessary to reach gas composition with (H2)/(H2O) approximately 10 at high temperature.

Makalkin, A. B.↗
NASA NTRS1993

Simultaneous laboratory measurements of CO2 and H2O adsorption on palagonite: Implications for the Martian climate and volatile reservoir

We are measuring the simultaneous adsorption of H2O and CO2 on palagonite materials in order to improve the formulation of climate models for Mars. We report on the initial co-adsorption data. Models of the Martian climate and volatile inventory indicate that the regolith serves as one of the primary reservoirs of outgassed volatiles and that it exchanges H2O and CO2 with the atmosphere in response to changes in insolation associated with astronomical cycles. Physical adsorbate must exist on the surfaces of the cold particulates that constitute the regolith, and the size of that reservoir can be assessed through laboratory measurements of adsorption on terrestrial analogs. Many studies of the independent adsorption of H2O and CO2 on Mars analog were made and appear in the literature. Empirical expressions that relate the adsorptive coverage of each gas to the temperature of the soil and partial pressure have been derived based on the laboratory data. Numerical models incorporate these adsorption isotherms into climatic models, which predict how the adsorptive coverage of the regolith and hence, the pressure of each gas in the atmosphere will vary as the planet moves through its orbit. These models suggest that the regolith holds several tens to hundreds of millibars of CO2 and that during periods of high obliquity warming of the high-latitude regolith will result in desorption of the CO2, and a consequent increase in atmospheric pressure. At lower obliquities, the caps cool and the equator warms forcing the desorption of several tens of millibars of CO2, which is trapped into quasipermanent CO2 caps.

Zent, A. P.↗
NASA NTRS1994

Simultaneous adsorption of CO2 and H2O under Mars-like conditions and application to the evolution of the Martian climate

The Martian regolith is the most substantial volatile reservoir on the planet; it holds CO2 as adsorbate, and can exchange that CO2 with the atmosphere-cap system over timescales of 10(exp 5) to 10(exp 6) years. The climatic response to insolation changes caused by obliquity and eccentricity variations depends in part on the total reservoir of adsorbed CO2. Previous estimates of the adsorbate inventory have been made by measuring the adsorptive behavior of one or more Mars-analyog materials, and deriving an empirical equation that described that adsorption as a function of the partial pressure of CO2 and the temperature of the regolith. The current CO2 inventory is that which satisfies adsorptive equilibrium, observed atmospheric pressure, and no permanent CO2 caps. There is laboratory evidence that H2O poisons the CO2 adsorptive capacity of most materials. No consideration of CO2 - H2O co-adsorption was given in previous estimates of the Martian CO2 inventory, although H2O is present in the vapor phase, and so as adsorbate, throughout the regolith.

Zent, Aaron P.↗
NASA NTRS1994

H2O-H2SO4 system in Venus' clouds and OCS, CO, and H2SO4 profiles in Venus' troposphere

A coupled problem of diffusion and condensation is solved for the H2SO4-H2O system in Venus' cloud layer. The position of the lower cloud boundary, profiles of the H2O and H2SO vapor mixing ratios, and of the H2O/H2SO4 ratio of sulfuric acid aerosol and its flux are calculated as functions of the column photochemical production rate of sulfuric acid. Variations of the lower cloud boundary are considered. Our basic model, which is constrained to yield f(sub H2O)(30km) = 30 ppm, predicts the position of the lower cloud boundary at 48.4 km coinciding with the mean Pioneer Venus value, the peak H2SO4 mixing ratio of 5.4 ppm, and the H2SO4 production rate phi(sub H2SO4) = 2.2 x 10(exp 12) cm(exp -2)s(exp -1).

Krasnopolsky, V. A.↗
NASA NTRS1997

Submillimeter and FIR CO and H2O line emission from collapsing protostellar envelopes

Computed far infrared (FIR) CO and H2O line spectra from collapsing envelopes around low mass protostars are presented. It is shown how high resolution observations of the CO and H2O rotational lines in the Far Infrared and Submillimeter Telescope (FIRST) wavelength range can be used to demonstrate the presence of infall, and to measure the central mass of the protostar. Selected H2O lines can be used to provide estimates of the mass accretion rate, and of the amount of water evaporated from the ice mantles and injected in the gas phase.

Ceccarelli, Cecilia↗
NASA NTRS2003

H2O-Silicate Microphysics in Ascending Volcanic Plumes on Mars

Physical adsorption of water vapor plays a much more significant role in eruptive plume energetics on Mars than on Earth. The total surface area in martian plumes is likely comparable to terrestrial ash, while the erupting magma and ambient atmosphere are drier. Plumes cool rapidly during ascent, and a limited population of H2O molecules find adsorption sites to be increasingly stable. Release of latent heat of condensation and the onset of moist convection are diminished, delayed, or even prevented by adsorptive interaction We have developed a 5-component numerical model of the behavior of water in eruptive plumes under Mars-like conditions. We have used the model to study the fate of both juvenile and ambient atmospheric water in the eruption column. Here we investigate the adsorptive interaction of water and silicates as they effect plume dynamics and the partitioning and distribution of H2O to the martian environment. Our focus is on the role of adsorption in scavenging H2O from the ascending eruption column, and the possibility that adsorptive scavenging depresses the vapor pressure in the column below the level considered in most eruptive models.

A P Zent↗
NASA NTRS2002

Ab initio calculations of anharmonic vibrational spectroscopy for hydrogen fluoride (HF)n (n = 3, 4) and mixed hydrogen fluoride/water (HF)n(H2O)n (n = 1, 2, 4) clusters

Anharmonic vibrational frequencies and intensities are computed for hydrogen fluoride clusters (HF)n, with n = 3, 4 and mixed clusters of hydrogen fluoride with water (HF)n(H2O)n where n = 1, 2. For the (HF)4(H2O)4 complex, the vibrational spectra are calculated at the harmonic level, and anharmonic effects are estimated. Potential energy surfaces for these systems are obtained at the MP2/TZP level of electronic structure theory. Vibrational states are calculated from the potential surface points using the correlation-corrected vibrational self-consistent field method. The method accounts for the anharmonicities and couplings between all vibrational modes and provides fairly accurate anharmonic vibrational spectra that can be directly compared with experimental results without a need for empirical scaling. For (HF)n, good agreement is found with experimental data. This agreement shows that the Moller-Plesset (MP2) potential surfaces for these systems are reasonably reliable. The accuracy is best for the stiff intramolecular modes, which indicates the validity of MP2 in describing coupling between intramolecular and intermolecular degrees of freedom. For (HF)n(H2O)n experimental results are unavailable. The computed intramolecular frequencies show a strong dependence on cluster size. Intensity features are predicted for future experiments.

Water/chemistry↗
NASA NTRS1986

Do the higher oxidation states of the photosynthetic O2-evolving system contain bound H2O?

A modified mass spectrometer was used to determine whether the higher oxidation states of the photosynthetic O2-evolving system contain substrate water that is not freely exchangeable with the external medium. Our data indicated that the higher oxidation states contain no appreciable bound, non-exchangeable H2O. This suggests that H2O oxidation takes place via a rapid, concerted, all-or-none mechanism rather than by a mechanism involving stable, partially oxidized, H2O-derived intermediates. These findings set definite constraints on possible mechanisms of O2 evolution.

NASA Discipline Life Support Systems↗
NASA NTRS1985

Determination of H2O and CO2 concentrations in fluid inclusions in minerals using laser decrepitation and capacitance manometer analysis

Water and carbon dioxide concentrations within individual and selected groups of fluid inclusions in quartz were analyzed by using laser decrepitation and quantitative capacitance manometer determination. The useful limit of detection (calculated as ten times the typical background level) is about 5 x 10(-10) mol of H2O and 5 x 10(-11) mol of CO2; this H2O content translates into an aqueous fluid inclusion approximately 25 micrometers in diameter. CO2/H2O determinations for 38 samples (100 separate measurements) have a range of H2O amounts of 5.119 x 10(-9) to 1.261 x 10(-7) mol; CO2 amounts of 7.216 x 10(-10) to 1.488 x 10(-8) mol, and CO2/H2O mole ratios of 0.011 to 1.241. Replicate mole ratio determinations of CO2/H2O for three identical (?) clusters of inclusions in quartz have average mole ratios of 0.0305 +/- 0.0041 1 sigma. Our method offers much promise for analysis of individual fluid inclusions, is sensitive, is selective when the laser energy is not so great as to melt the mineral (laser pits approximately 50 micrometers in diameter), and permits rapid analysis (approximately 1 h per sample analysis).

Water/analysis↗
NASA NTRS2015

A Novel Triple-Pulsed 2-micrometer Lidar for Simultaneous and Independent CO2 and H2O Column Measurement

The study of global warming needs precisely and accurately measuring greenhouse gases concentrations in the atmosphere. CO2 and H2O are important greenhouse gases that significantly contribute to the carbon cycle and global radiation budget on Earth. NRC Decadal Survey recommends a mission for Active Sensing of Carbon Dioxide (CO2) over Nights, Days and Seasons (ASCENDS). 2 micron laser is a viable IPDA transmitter to measure CO2 and H2O column density from space. The objective is to demonstrate a first airborne direct detection 2 micron IPDA lidar for CO2 and H2O measurements.

Yu, Jirong↗
NASA NTRS2022

The Abundances of F, Cl, and H2O in 4Vesta from Eucrites

The abundance and distribution of magmatic volatiles (i.e., H, C, N, F, S, and Cl) within the silicate portion of a differentiated planetary body has important consequences on its thermochemical evolution. However, the abundances of magmatic volatiles within differentiated bodies are difficult to quantify, and they are often depleted by varying degrees relative to CI chondrites. The mechanisms of depletion are not well constrained and could relate to intrinsic volatile depletion of the building blocks that formed the bodies, high temperature processes that result from accretion, post-accretion loss through parent body geological processes and large-scale impacts, and/or redistribution within a parent body through processes like core formation [1–4]. In the present study, we aim to constrain the abundances of F, Cl, and H2O in eucrites to better understand the magnitude of volatile depletion on 4Vesta. To accomplish this objective, we report electron microprobe analyses of apatite from seven unbrecciated, non-cumulate eucrites (i.e., CMS 04049,GRA 98098, LEW 88010, MAC 02522, MAC 041169,QUE 94484, and QUE 97053) and two monomict, non-cumulate eucrites (i.e., Berthoud and Stannern). In combination with previously published data on eucrite-hosted apatite, we determine Cl/F and H2O/F ratios in bulk rock eucrites through the application of apatite-based melt hygrometry and chlorometry [e.g., 5–7].Additionally, we estimate the bulk rock abundances of F in six non-cumulate eucrites (i.e., GRA 98098, MAC041169, PCA 91078, QUE 97053, Stannern, and Berthoud), which we combine with previously published bulk rock F data on non-cumulate eucrites[8] to constrain the abundances of F, Cl, and H2O in 4Vesta using appropriately paired volatile/refractory element ratios for F, followed by Cl/F and H2O/F ratios for Cl and H2O, respectively.

F M McCubbin↗
NASA NTRS1973

Development of an H2O atmosphere around Comet Kohoutek /1973f/ and its possible detection.

Although chemically stable 'parent molecules' for the observed radicals in comets, have been suspected for more than thirty years none of them has yet been observed spectroscopically. The newly discovered great comet Kohoutek may provide an excellent opportunity for directly observing a 'parent molecule' (namely, H2O) for the first time. The continuous development of a H2O atmosphere around the nucleus as the comet approaches the sun is discussed together with the detection of this atmosphere, using ground-based instruments and instruments carried in aircraft, balloons, and rockets.

Ip, W.-H.↗
NASA NTRS1973

Mars - Mariner 9 spectroscopic evidence for H2O ice clouds

Spectral features observed with the Mariner 9 interferometer spectrometer are identified as those of H2O ice. The measured spectra are compared with theoretical calculations for the transfer of radiation through clouds of ice particles with variations in size distribution and integrated cloud mass. Comparisons with an observed spectrum from the Tharsis Ridge region indicate H2O ice clouds composed of particles with a mean radius of 2.0 microns and an integrated cloud mass of .00005 g/sq cm.

Curran, R. J.↗
NASA NTRS1974

Time variation of the H2O maser and infrared continuum in late-type stars

Observations of the variability of the 1.35-cm H2O and 2.2-micron emission from eight late M stars are described. A comparison of the microwave and infrared variations is of interest because the bulk of the stellar energy is radiated in the near-infrared and because at least one theory (Litvak 1969) hypothesizes near-infrared maser pumping via the 2.7-micron H2O vibration-rotation band. Variations at the two wavelengths appear to be correlated and possible explanations for this correlation are discussed.

Schwartz, P. R.↗
NASA NTRS1974

A search for H2O and CH4 in Comet Kohoutek

A spectroscopic search for H2O and CH4 in Comet Kohoutek (1973f) was made using a Pepsios interferometer. No evidence was found for either molecule, allowing to set an upper limit on their production rates (on about Jan. 21, 1974) of Q(H2O) less than 6.2 times 10 to the 28th power per sec and Q(CH4) less than 20 times 10 to the 30th power per sec.

Traub, W. A.↗
NASA NTRS1977

On the relationship between the infrared source CRL 2591 /UOA-27/ and its radio and H2O counterparts

Recent radio, infrared, and H2O maser observations show that there is a 7-arcsec angular separation between the protostarlike infrared source CRL 2591 and the compact H II region which has until now been identified with it, while the H2O maser coincides with the infrared source. This result, together with an extension of photometric measurements to 20 microns and a much improved upper limit to its angular size, reinforces the apparent similarity of CRL 2591 to the BN object in Orion and to W3/IRS 5.

Wynn-Williams, C. G.↗
NASA NTRS1979

Lyman-alpha and Balmer-series fluorescence from hydrogen photofragments of H2O vapor

Production cross sections associated with the atomic hydrogen Lyman-alpha and Balmer-series (3-9 to 2) fluorescence observed in H2O photodissociation are measured, and maximum fluorescence production cross sections for the two series are reported. Repulsive potential energy curves corresponding to the respective pseudodiatomic OH-H(n) molecule are constructed according to the Franck-Condon principle, and the efficiencies for converting H(2S) to H(2P) by H2 collisions and by H2O collisions are estimated. The data are considered with reference to cometary photochemistry.

Wu, C. Y. R.↗
NASA NTRS1979

Interstellar bullets - H2O masers and Herbig-Haro objects

The paper considers the energy input to H2O masers in a dense molecular cloud and analyzes the response time scales for both collisional and radiative pump models. Specific mechanisms for magnetic energy input are given. The evolution of dense H2O maser clouds is studied in the environment of a young pre-main-sequence star that has developed an appreciable supersonic wind. It is shown that compact clouds can be ejected at high velocity to distances of order 1 pc. It is suggested that these clouds (referred to as interstellar bullets) might explain the phenomena of Herbig-Haro objects and high-velocity gas motions observed near compact infrared objects.

Norman, C.↗