Escape Of Oxygen Research Articles

A model of the ionospheric tail rays of Venus

Distinctive structural patterns in the "tail rays" that form the outermost reaches of the Venus nightside ionosphere were observed on the Pioneer Venus Orbiter. The measurements further suggested that the tail rays are the vehicle for significant escape of atmospheric oxygen, but the manner in which they fit into the scenario of solar wind scavenging and the physics behind their formation remain unexplained. In this paper a model of tail ray generation and morphology is proposed which is based on knowledge of the magnetic field structure in the low‐altitude magnetosheath and near‐wake, where the tail rays are observed. The model applies specifically to those regions where the plasma pressure in the tail rays is less than the field pressure. It is shown that many of the observed structural patterns can be explained if it is assumed that initially low energy ionospheric O+ ions are picked up by an externally imposed convection electric field from a thin source region around the terminator. Gravity is found to play a significant role in determining the ion trajectories and hence the modeled tail ray structures. The model can produce single, double, triple, or quadruple thin tail rays, all of which are observed. The energies of the particles are also consistent with the available data. The reported tail ray dependence on solar EUV flux and solar wind dynamic pressure naturally fits into the proposed concept. The implication for ion escape is that no special mechanisms are required to explain Venus tail rays. They may be simply interpreted as the low‐altitude, low‐energy manifestation of the standard ion pickup process at a weakly magnetized planet.

On the escape of oxygen and hydrogen from Mars

Escape rates of oxygen atoms from dissociative recombination of O2+ above the Martian exobase are computed in light of new information from ab initio calculations of the dissociative recombination process, and our recently revised understanding of the Martian dayside ionosphere. Only about 60% of the dissociative recombinations occur in channels in which the O atoms are released with energies in excess of the escape velocity. Futhermore, we find that the computed escape fluxes for O depend greatly on the nature of the ion loss process that has been found necessary to reproduce the topside ion density profiles measured by Viking. If it is assumed that the ions are not lost from the gravitational field of the planet, as required by an analysis of nitrogen escape, the computed average O escape rate is 3 × 106 cm−2 s−1, much less than half the H escape rates inferred from measurements of the Lyman alpha dayglow, which are in the range (1 – 2) × 108 cm−2 s−1. Suggestions for restoring the relative escape rates of H and O to the stoichiometric ratio of water are explored. The final resolution of this problem may have to await a future aeronomy mission to Mars.

Mars volatile evolution: Implications of the recent measurement of 17O in water from the SNC meteorites

Escape of oxygen to space on Mars is capable of producing a fractionation of oxygen isotopes in the remaining oxygen which is off of the fractionation line produced by the usual mass‐dependent exchange processes. The magnitude of fractionation which can occur can be larger than that which was measured in oxygen in water derived from the SNC meteorites (thought to have come from Mars). In conjunction with the apparent lack of fractionation of 18O in the atmosphere, this result suggests that less than 25% of the oxygen in the martian climate system has been lost over geologic time. Other mechanisms also might be able to produce such a fractionation, so that this conclusion is not unique; however, it is consistent with other lines of evidence. There is no requirement for an initial volatile inventory with an isotopic composition different from that of the bulk planet (as might be the case for a late veneer of volatile‐rich material).

Mechanism of ligand binding to hemes and hemoproteins. A high-pressure study

The effect of pressure on the recombination kinetics of small ligands binding to sperm whale myoglobin, protoheme dimethyl ester, and monochelated protoheme was studied with use of laser flash photolysis. The volumes of activation observed indicate that in both the protein and the models bond formation is the rate-determining step only for carbon monoxide, while for oxygen, isocyanides, and 1-methylimidazole almost no bond formation occurs in the transition state of the observed reaction. The effect of pressure on the escape of carbon monoxide, oxygen, and methyl isocyanide from the heme pocket of sperm whale myoglobin was also investigated

Studies of adsorption and electron-induced dissociation of Fe(CO) 5 on Si(100)

The adsorption and electron-stimulated decomposition properties of Fe(CO) 5 on Si(100) have been investigated. At substrate temperatures in the range 77–300 K, no chemisorption states are populated to a detectable extent. Physisorption at 77 K is observed, with a sticking probability of ≈ 0.2; TDS indicates that the heat of adsorption is constant at 33 ± 4 kJ mol −1 both in the monolayer and multilayer regimes and the desorption kinetics are suggestive of island formation. Prominent electron-stimulated desorption (ESD) and decomposition effects have been investigated. Fe(CO) 5 multilayers decompose by rapid ESD of iron carbonyls, whilst monolayer decomposition involves the evolution of O and CO species in a stepwise manner from the parent molecule. Cross-sections for the processes occurring are evaluated; the electron stimulated rate of FeCO bond cleavage is demonstrated to be more rapid than the rate of escape of oxygen containing entities from the surface and this is explained in terms of bond orientation effects.

Photolysis of water with supported noble metal clusters, the fate of oxygen in titania based water cleavage systems

Controlled thermal decomposition of (Rh) 6(CO) 16 clusters in the presence of TiO 2 (anatase) yields highly active catalysts which decompose water under illumination by a solar simulator with an overall light to chemical energy conversion efficiency of 0.12%. In this system escape of oxygen in the gas phase is prevented by O 2-photo-uptake yielding a peroxo-titanium complex, probably μ-peroxo type, which dissolves in 1 M NaOH but remains on the TiO 2 Particle surface under neutral conditions. The cyclic fashion in which these systems operate suggests that the peroxo-complex releases O 2 in a reversible fashion upon flushing with an inert gas. The oxygen carrier function of the TiO 2 particles is confirmed by quantitative titration with permanganate and experiments comparing hydrogen-oxygen recombination under light and in the dark.

Escape of sulfur and oxygen from Io

Charged particle sputtering is reexamined as a mechanism for escape of sulfur and oxygen from Io. Corotating ions and energetic ions are considered, using the best available determinations of ion fluxes and sputtering yields. It is unclear whether molecular SO2 is the dominant escaping neutral from Io or whether atomic O and S are dominant, but the Voyager detection of SO2+ in the cold torus implies the presence of molecular SO2 there. Thin atmosphere models encounter serious difficulty in achieving adequate sulfur and oxygen escape rates, but they are not yet ruled out. Ionization and dissociation of SO2 in a sputter corona can dominate direct escape. In thick atmosphere models the neutral escape rates can be much higher, but the oxygen escape rate tends to be too high relative to the sulfur escape rate unless diffusive separation in the atmosphere is limited, perhaps by rapid mixing.

Explosion-proof operating conditions for a liquid oxygen evaporator

An operating test of air rectifiers has shown that the most common cause of normal operation breakdowns is the escape of oxygen from the evaporator system. Explosive conditions develop in oxygen evaporators because the atmospheric air fed into the rectifier contains explosive impurties. The paper deals with the accumulation of explosive impurities in heterogeneous form in oxygen evaporators. Studies carried out show that the rate of heterogeneous accumulation of explosive impurities in the evaporators depends to a large degree on the hydrodynamic conditions of liquid conditions of evaporation, especially on the rate at which the liquid moves relative to the vaporizer surface. The accumulation rate on smooth vapor-generating surfaces of all the evaporator designs studied was proportional to the time of operation under the specified hydrodynamic conditions. Calculations and experimental data indicate that under favorable hydrodynamic conditions and under the hydrocarbon concentrations observed in real evaporators operating with liquid oxygen, the time necessary to accumulate an explosive hydrocarbon layer is 2 to 4 months of continuous operation. The evaporators used in recent years in air rectifiers have a heating surface covered with a porous metallized layer. The hydrocarbon accumulation rate on such surfaces decreases sharply with time, and there ismore » therefore no danger when explosive impurities present in the system accumulate in a porous metallized layer.« less

Stability of an oxygen atmosphere on ganymede

Photolysis of water and subsequent escape of hydrogen can give rise to an oxygen atmosphere on Ganymede. Growth of the atmosphere may be limited by escape of fast oxygen atoms formed by photodissociation of O 2. Escape of oxygen and hydrogen in an equilibrium configuration should balance net evaporation of water from the satellite's surface and the partial pressure of atmospheric O 2 could be as high as 10 −3 mbar. Ganymede should have lost an appreciable quantity of water over geologic time, enough to have coated the surface of the satellite with ice to a depth of about 2 m. An oxygenatmosphere with similar properties might be expected to occur also on Callisto.

Oxygen isotopes in the martian atmosphere: Implications for the evolution of volatiles

Non-thermal escape of oxygen by recombination of exospheric O 2 + combined with diffusive separation of gases at lower altitude provides a mechanism through which the Martian atmosphere may be enriched in 18O relative to 16O. Measurement of the abundance of 18O relative to 16O together with a determination of the turbopause may be used to develop important constraints on the history of Martian volatiles. Models for the interpretation of these data are developed and discussed in light of present information.

Escape of fast oxygen from the atmosphere during geomagnetic storms

Observations have been reported of energetic O+ fluxes (0.7–12 keV with energy fluxes of up to 0.4 erg cm−2 s−1 sr−1) during several magnetic storms. We examine the atmospheric effects to be expected from the precipitation of these fluxes. The fast O+ ions produce fast O atoms through charge exchange and momentum transfer (yielding atomic oxygen emissions that may be as bright as 200 R). The fast oxygen atoms lose their energy largely through momentum transfer collisions with ambient oxygen atoms. This process produces a large shower of low-energy nonthermal oxygen atoms and results in heating of the atmosphere above 200 km. A substantial number of these oxygen atoms have sufficient energy to escape from the atmosphere. If this type of precipitation event occurs frequently enough, the escape mechanism could result in a significant loss of atmospheric oxygen over the lifetime of the earth.

Notice

Abstract The distributions of dissolved oxygen, density, and nutrients off the Washington and Oregon coasts are complicated by upwelling, entrainment of deep water, the presence of Columbia River water, biological activity, in-situ temperature changes, and possibly by anomalous surface exchanges associated with wave action. In much of the area there is a good statistical correlation between the dissolved oxygen and the density, except in the upper layers of the coastal region, where large negative oxygen anomalies were found. These anomalies were used to evaluate changes in the oxygen content resulting from biological activity and mixing associated with upwelling. An offshore, downward advection of water bearing excesses of oxygen photosynthetically produced in the surface layers near shore, is proposed to explain an oxygen maximum that occurs subsequent to the oxygen's production and at depths that increase with distance from shore. Seasonal variations in this maximum are explained in terms of the balance between the rates of oxygen addition by photosynthesis and the oxygen flux associated with upwelling during the spring and summer, and diffusional erosion of the maximum during periods of more modest photosynthesis. Simultaneous observations of oxygen and nutrients can yield useful information regarding the biological activity in the surface waters. A first approximation at evaluating the biological changes in the oxygen can be made by assuming that a linear relationship exists between it and changes in nutrient concentrations. Since the nutrients will not be appreciably exchanged with the atmosphere, departures from this linear relationship are assumed to result from the effect of in-situ temperature changes on calculated oxygen solubilities and the escape of oxygen to the atmosphere. In areas of intense photosynthesis these departures are small, suggesting that in such regions oxygen production outstrips the escape rate. Under such conditions a good correlation is also found between the carbon-14 assimilation and the apparent oxygen production. On the other hand, low oxygen concentrations, compared to saturation values, coinciding with low nutrients indicate more modest photosynthesis.

Distributions of dissolved oxygen, density, and nutrients off the Washington and Oregon coasts

The distributions of dissolved oxygen, density, and nutrients off the Washington and Oregon coasts are complicated by upwelling, entrainment of deep water, the presence of Columbia River water, biological activity, in-situ temperature changes, and possibly by anomalous surface exchanges associated with wave action.In much of the area there is a good statistical correlation between the dissolved oxygen and the density, except in the upper layers of the coastal region, where large negative oxygen anomalies were found. These anomalies were used to evaluate changes in the oxygen content resulting from biological activity and mixing associated with upwelling.An offshore, downward advection of water bearing excesses of oxygen photosynthetically produced in the surface layers near shore, is proposed to explain an oxygen maximum that occurs subsequent to the oxygen's production and at depths that increase with distance from shore. Seasonal variations in this maximum are explained in terms of the balance between the rates of oxygen addition by photosynthesis and the oxygen flux associated with upwelling during the spring and summer, and diffusional erosion of the maximum during periods of more modest photosynthesis.Simultaneous observations of oxygen and nutrients can yield useful information regarding the biological activity in the surface waters. A first approximation at evaluating the biological changes in the oxygen can be made by assuming that a linear relationship exists between it and changes in nutrient concentrations. Since the nutrients will not be appreciably exchanged with the atmosphere, departures from this linear relationship are assumed to result from the effect of in-situ temperature changes on calculated oxygen solubilities and the escape of oxygen to the atmosphere. In areas of intense photosynthesis these departures are small, suggesting that in such regions oxygen production outstrips the escape rate. Under such conditions a good correlation is also found between the carbon-14 assimilation and the apparent oxygen production. On the other hand, low oxygen concentrations, compared to saturation values, coinciding with low nutrients indicate more modest photosynthesis.

Upper Atmospheres of the Planets.

view Abstract Citations (40) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Upper Atmospheres of the Planets. Chamberlain, Joseph W. Abstract Most of our knowledge of the earth's upper atmosphere is obtained from experiments in sit or remote observations that offer fairly direct interpretations. For the other planets, neither approach is as yet possible; so indirect, theoretical procedures are required to construct models of their atmospheres. Herein the wide variety of basic physical processes governing the structure of a planetary high atmosphere are set forth, with a view toward obtaining "deductive models' `-i e, models derived theoretically when only the chemical composition and temperature of the lower atmosphere and the incident solar flux are specified (in addition to various physical and astronomical constants). The procedures are applied to Mars, whose lower and middle atmosphere is already partially understood from earlier work, notably that of R. Goody. The uncertainties involved at various stages in the construction of such a model are emphasized, as are the major differences in physical processes and atmospheric characteristics between Mars and the earth. The most significant result is that the CO that must be in the upper atmosphere of Mars should serve as an effective thermostat, keeping the temperature at the escape level (1500 km) from exceeding about 11000 K. This is cool enough for Mars to retain atomic oxygen. Were it not for CO cooling, the upper atmosphere of Mars would be so extensive and form such an effective thermal insulation between the upper ionosphere and the heat sink at the mesopause that the temperature would exceed 20000 K. lifetime for the escape of oxygen is estimated as 10 years. The mesopause is determined by CO2 radiation. Near the mesopause CO2 should become dissociated and the free 0 atoms form a thin layer of O this effect has no analogy on earth. The model ionosphere has considerably smaller densities of ionization than comparable regions in the earth's atmosphere The E region is split into two distinct portions, with X-rays forming the higher one (E2) and ultraviolet light ionizing Oi near the mesopause (E1) The Martian analogue to the terrestrial F2 region may not develop a very high electron density, and the entire ionosphere should be depleted at night. Publication: The Astrophysical Journal Pub Date: September 1962 DOI: 10.1086/147409 Bibcode: 1962ApJ...136..582C full text sources ADS |

Oxygen Therapy Equipment-Reply

To the Editor:— The development of safe transfilling equipment was stimulated by the increasing use of ambulatory and emergency oxygen therapy. In the device referred to in the article cited, the 75- and 150-liter cylinders are equipped with a check valve which closes after the cylinder is filled and the transfilling device is disconnected. Of special importance is the fact that the orifice past the check valve is 0.003 sq. in. in area. The small size of this outlet prevents a projectile effect on the portable cylinders if a break in the connection should occur. The capillary tubing between the small and large cylinders is 0.02 in. in diameter. It has been recommended that a diaphragm check valve also be inserted at the nut connection to the large cylinder, the purpose of which would be to automatically shut off the escape of oxygen should the flow exceed 15 liters per

The atmosphere and haze of Mars

The ‘blue haze’ is an absorbing smoke, dark as soot in reflection, red in transmission. Its currently accepted explanation by pure scattering (omnidirectional or forward) is untenable, as it would either increase the surface brightness or fail to obscure the surface details. The limb darkening of Mars is mainly the result of absorption by the smoke. The opacity of the Martian atmosphere increases from the red toward the violet. The extinction by the Martian atmosphere is greater than that by the terrestrial at all wavelengths, but only about 20 per cent of the Martian extinction is due to scattering. Dollfus' polarimetric estimate, corrected for self-absorption, corresponds to a Martian atmospheric pressure of 87 mm Hg. The photochemical breakup of carbon dioxide and the escape of oxygen must lead to considerable concentrations of carbon monoxide in the Martian atmosphere.