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At least 451 records · Page 25

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NASA NTRS1986

Effect of the greenhouse gases (CO2, H2O, SO2) on Martian paleoclimate

There is general agreement that certain surface features on Mars are indicative of the presence of liquid water at various times in the geologic past. In particular, the valley networks are difficult to explain by a mechanism other than the flow of liquid water. It has been suggested in several studies that a thick CO2 atmosphere on Mars early in its history could have provided a greenhouse warming that would have allowed the flow of water either on the surface or just below the surface. However, this effect was examined with a detailed radiation model, and it was found that if reduced solar luminosity early in the history of the solar system is taken into account, even three bars of CO2 will not provide sufficient greeenhouse warming. The addition of water vapor and sulflur dioxide (both plausible gases that may have been emitted by Martian volcanoes) to the atmosphere also fail to warm the surface above 273 K for reduced solar luminosity conditions. The increase in temperature may be large enough, however, for the formation of these features by brines.

Postawko, S. E.↗

NASA NTRS1986

Measurement of H2O and other trace gases in the stratosphere using a high resolution far-infrared spectrometer at 28 KM

The highlights of the stratospheric program were reviewed for the past 2.5 years. The major efforts were analysis of the data from the BIC-2 campaign, and the building or new instrumentation to replace that lost at the end of BIC-2. For clarity, the review will be done by topic, rather than chronologically: construction of the initial far-infrared spectrometer, balloon slight program, laboratory measurement, data analysis, and duplicate stabilized platform.

Traub, W. A.↗

NASA NTRS1987

Investigation of Martian H2O and CO2 via gamma-ray spectroscopy

The evolution and present state of water and carbon dioxide on Mars are discussed. Researchers wished to determine how effectively questions regarding the distribution of water and carbon dioxide on Mars may be addressed with orbital gamma ray spectrometer data. Several simple, multi-layer models of the Martian surface were formulated to address problems such as the ice/dust ratio of layered deposits; the distribution, depth and concentration of ground ice; the thickness of north polar perennial ice; the thickness of the carbon dioxide layer over the south polar cap; the thickness of the seasonal carbon dioxide frost cap; and the water content of the seasonal frost cap. The results indicate that the Mars Observer gamma ray spectrometer will be a powerful tool for investigating the distribution and stratigraphy of volatiles on Mars.

Squyres, Steven W.↗

NASA NTRS1987

Effects on H(-) production in a multicusp ion source by mixture of H2 with H2O, NH3, CH4, N2H4, and SF6

Effects of H(-) production in a multicusp ion source are measured by separately mixing with hydrogen small amounts (0.33-10 percent) of water, ammonia, methane, and hydrazine these are molecules which produce large amounts of H(-) via dissociative attachment (DA) resonances at higher electron energies. The mixing was done in a separate reservoir, with careful measurement of individual pressures. Experimental enhancements of 1.4 and less were observed, whereas calculated enhancements, using accurate DA cross sections for ground-state H2, should have produced factors of 1.5, 3.0, 1.3, and 2.4 enhancements for water, ammonia methane, and hydrazine, respectively, at a mean electron energy of 1.0 eV in the extraction region. The difference is accounted for by including, in the enhancement calculation, vibrationally and rotationally excited H2 molecules, with v-double prime = 5-11, and J-double prime = 0-5, and the large DA cross sections for the excited H2 (v-double prime, J-double prime). The relative populations of H2 (v-double prime, J-double prime) thus obtained are found to be substantially smaller than those predicted by theoretical calculations. The effect on H(-) current was also studied by mixing small amounts of SF6 with H2. A 1.5 percent mixture was found to reduce the H(-) output by one half.

Orient, O. J.↗

NASA NTRS1986

A lidar instrument to measure H2O and aerosol profiles from the NASA ER-2 aircraft

Plans to develop the Lidar Atmospheric Sensing Experiment (LASE) instrument to conduct scientific experiments aboard a NASA U-2 (ER-2) aircraft are described. The LASE measurement objectives are listed, and the design of the LASE instrument is discussed, including performance criteria for the laser transmitter, wavemeter, telescope, optical receiver, and associated electronics. The instrument function is depicted with a block diagram, and layouts of various components are presented.

Vaughan, W. R.↗

NASA NTRS1988

Infrared reflectance spectra of Na2S with contaminant Na2CO3 - Effects of adsorbed H2O and CO2 and relation to studies of Io

A previously reported laboratory determination of the IR spectrum of Na2S is presently noted to have been incorrectly interpreted, due to the inadvertent contamination of the sample with Na2CO3. New Na2S spectra are presented, and the Na2CO3 spectrum is examined in order to demonstrate that this phase is the primary sample contaminant. Na2S is a candidate surface component on the Jupiter satellite, Io, in view of its apparent high IR brightness and spectral neutrality in the 1-5 micron range.

Nash, Douglas B.↗

NASA NTRS1988

Antarctic ozone depletion chemistry - Reactions of N2O5 with H2O and HCl on ice surfaces

In a study concerning Antarctic ozone depletion, reactions of dinitrogen pentoxide with water and hydrochloric acid were studied on ice surfaces in a Knudsen cell flow reactor. The N2O5 reacted on ice at 185 K to form condensed-phase nitric acid (HNO3). This reaction may provide a sink for odd nitrogen, NO(x), during the polar winter, a requirement in nearly all models of Antarctic ozone depletion. The reaction of N2O5 on HCl-ice surfaces at 185 K produced gaseous nitryl chloride (ClNO2) and condensed-phase HNO3 and proceeded until all of the HCl within the ice was depleted. The ClNO2 which did not react or condense on ice at 185 K, can be readily photolyzed in the Antarctic spring to form atomic chlorine for catalytic ozone destruction cycles. The other photolysis product, gaseous nitrogen dioxide may be important in the partitioning of NO(x) between gaseous and condensed phases in the Antarctic winter.

Tolbert, Margaret A.↗

NASA NTRS1988

Channel formation in Pb-Sn, Pb-Sb, and Pb-Sn-Sb alloy ingots and comparison with the system NH4Cl-H2O

The formation of segregation channels during the unidirectional solidification of base chilled ingots has been studied as a function of composition in binary Pb-Sn and Pb-Sb and ternary Pb-Sn-Sb alloys. The patterns of channel distribution were characterized in the binary and ternary systems and are described as functions of temperature gradients, growth rates, dendrite spacings, and interdendritic permeabilities. Channels appear to nucleate at random across a dendritic front and subsequently to interact as they propagate, decreasing in density across the front. Assuming that the interdendritic spacing is the characteristic distance for a liquid perturbation, yields critical effective Rayleigh numbers which lie within a factor of x 40 for both metallic and aqueous systems. This correlation is close, considering the sensitivity to any assumed dimension and the range of material properties involved, and is taken to support a model for channel nucleation occurring close to the dendritic growth front.

Hellawell, A.↗

NASA NTRS1988

MECA Workshop on Atmospheric H2O Observations of Earth and Mars. Physical Processes, Measurements and Interpretations

The workshop was held to discuss a variety of questions related to the detection and cycling of atmospheric water. Among the questions addressed were: what factors govern the storage and exchange of water between planetary surfaces and atmospheres; what instruments are best suited for the measurement and mapping of atmospheric water; do regolith sources and sinks of water have uniquely identifiable column abundance signatures; what degree of time and spatial resolution in column abundance data is necessary to determine dynamic behavior. Of special importance is the question, does the understanding of how atmospheric water is cycled on Earth provide any insights for the interpretation of Mars atmospheric data.

Clifford, Stephen M.↗

NASA NTRS1988

Possible significance of cubic water-ice, H2O-Ic, in the atmospheric water cycle of Mars

The possible formation and potential significance of the cubic ice polymorph on Mars is discussed. When water-ice crystallizes on Earth, the ambient conditions of temperature and pressure result in the formation of the hexagonal ice polymorph; however, on Mars, the much lower termperature and pressures may permit the crystallization of the cubic polymorph. Cubic ice has two properties of possible importance on Mars: it is an excellant nucleator of other volatiles (such as CO2), and it undergoes an exothermic transition to hexagonal ice at temperatures above 170 K. These properties may have significant implications for both martian cloud formation and the development of the seasonal polar caps.

Gooding, James L.↗

NASA NTRS1988

Circumpolar hoods and clouds and their relation to the Martian H2O cycle

Water exists in both vapor and solid phases in the Martian atmosphere. The polar hoods are shrouds of condensate clouds which obscure both polar regions at times during their respective fall and winter seasons. The hemispheric asymmetries in the polar hood clouds are reviewed and their significance to the seasonal water cycle is discussed. Comparisons of images acquired using short wavelength filters, which provide maximum cloud contrast, and long wavelength filters, which are sensitive to surface features including the surface cap, provide correlations between cloud formation and large scale planetary dynamics.

James, Philip B.↗

NASA NTRS1988

Measurements of H2O in the terrestrial mesosphere and implications for extra-terrestrial sources

Recent measurements of mesospheric water vapor and their implications for the existence of extraterrestrial sources of water are discussed. This study was prompted by the work of L. Frank and others who, based on their interpretation of transient dark spots visible in ultraviolet images of the Earth's dayglow emission, have proposed that a large flux of small comets enters the Earth's upper atmosphere each day. To date, however, analysis does not conclusively refute or support the idea of an external source.

Olivero, John J.↗

NASA NTRS1988

Diurnal and annual cycles of H2O in the Martian regolith

The atmospheric heat engines of Earth and Mars are compared. Although water latent heat transfer drives the circulation of the Earth's atmosphere, particularly in the tropics, its contribution to the circulation of the martian atmosphere is negligible. The working fluid on Mars is CO2, which exerts its greatest influence on atmospheric circulation at the poles. The diurnal and seasonal flux of water within the martian regolith is also examined. Calculations indicate that, for a mean annual temperature of 200 K, a diurnal and annual temperature variation of 30 K will drive a maximum exchange of 1.2 pr micrometer and 120 pr micrometer of water, respectively.

Philip, John R.↗

NASA NTRS1988

Atmospheric H2O and the search for Martian brines

Abundant martian brines would have important implication for current theories of volatile migration on Mars, since, although the presence of metastable brines is quite plausible, any brine in the reasonably near-surface should be completely depleted on a timescale short in relation to the age of Mars. It is important to determine whether brines exist in the martian subsurface, for the current paradigm for understanding martian volatile regime requires substantial alteration if they are found to exist. It is determined, however, that the prospect for detection of a subsurface brine via atmospheric water vapor measurements is marginal. Four reasons are given for this conclusion.

Zent, Aaron P.↗

NASA NTRS1988

A study of H2O ice in the 3 micron spectrum of OH 231.8+4.2 (OH 0739-14)

Moderate resolution IR spectra of OH 231.8+4.2 in the 2.0-3.8-micron spectral region are presented. It is shown that the large-scale features of the observed spectra can only be modeled with an unusually large upper limit to the grain-size distribution (0.6-0.7 microns). Two new absorption features have been found in the wings of the 3.08-micron feature, near 2.95 and 3.2 microns. The results suggest that a mixture of amorphous and crystalline ice may have produced the 3.08-micron feature in this object.

Smith, Robert G.↗

NASA NTRS1988

Multichannel processes of H2O in the 18 eV region

Measurements were made of: (1) the fluorescence cross sections of OH(A 2Sigma+) fragments; (2) the absolute cross sections producing H atoms in the n = 2, 3, and 4 states; (3) the cross section for producing excited O atoms which has an upper limit of 5 x 10 to the -21 sq cm; and (4) the fluorescence cross section for producing H2(a 3Sigma g +) fragments. It is shown that, in the 16-20 eV region, there are excellent correspondences in the peak positions and spacings among the photoabsorption, photoionization spectra, and fluorescence functions of OH(A) and H(n).

Wu, C. Y. Robert↗

NASA NTRS1990

Enhancement of Pt/SnO2 Catalysts by Addition of H2O

Water vapor in pretreatment gas restores essential hydroxyl groups. Platinum on tin oxide (Pt/SnO2) is good catalyst for oxidation of carbon monoxide (CO) at temperatures from about 25 degrees C to 100 degress C. Activity of Pt/SnO2 for CO oxidation significantly enhanced by pretreating it at approximately 225 degrees C with reducing gas such as CO. Technique useful in manufacture of high-power CO2 lasers for industrial and scientific uses.

Schryer, David R.↗

NASA NTRS1990

The effect of H2O and pretreatment on the activity of a Pt/SnO2 catalyst

CO oxidation catalysts with high activity at 25 C to 100 C are important for long-life, closed-cycle operation of pulsed CO2 lasers. A reductive pretreatment with either CO or H2 has been shown to significantly enhance the activity of a commercially available platinum on tin (IV) oxide (Pt/SnO2) catalyst relative to an oxidative or inert pretreatment or no pretreatment. Pretreatment at temperatures of 175 C and above causes an initial dip in the observed CO2 yield before the steady-state yield is attained. This dip has been found to be caused by dehydration of the catalyst during pretreatment and is readily eliminated by humidifying the catalyst or the reaction gas mixture. It is hypothesized that the effect of humidification is to increase the concentration of OH groups on the catalyst surface which play a role in the reaction mechanism.

Vannorman, John D.↗