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At least 469 records · Page 26
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NASA NTRS1986

Studies of extended planetary atmospheres

Telescopic observations were made of gases and plasmas in the Jupiter system, and related phenomena such as the recently-discovered sodium atmosphere of Mercury. Sodium absorption in Io's atmosphere was observed to distances as large as 5 Io radii during the mutual-eclipse season of the Jovian satellites. Analysis of Jovian disk spectra has proceeded, as planned, from an emphasis on the H2 ortho-para ratio to analysis of methane absorptions and determination of cloud structure. Several 2-channel photometers were constructed in 1978 for the Uranus event at which the rings were discovered and a smaller, single-channel unit was built more recently. Although the photometers themselves are still fully usable, the data-acquisition systems have major deficiencies.

Hunten, D. M.↗
NASA NTRS1986

Radiative transfer in planetary atmospheres

The research effort was concentrated toward comet P/Halley, although observations of other comets including Giacobini-Zinner, Hartley-Good and Thiele were made as opportunities arise. In preparing for the apparition of P/Halley, detailed predictions for the emission in the 18 cm OH transitions were made in order to assist observers and to indicate what type of data would be particularly valuable. Likewise, since occultations by the comet of background radio sources can provide unique types of information, the tracks of P/Halley and P/Giacobini-Zinner were surveyed with the NRAO Very Large Array, background sources were mapped, and a catalogue of occulted sources published. Beginning in September, 1985, regular observations of the 18 cm OH lines have been made for P/Halley using the 43 m antenna of the NRAO in Greenbank, West Virginia. These data promise to provide the most accurate time sequence for the OH emission for any comet ever obtained at radio wavelengths. From the linewidth and shape, information is obtained on the kinetics of the gas in the cometary coma. An extensive series of observations have been undertaken with 14 m antenna to study emission from the HCN molecule in P/Halley. These data provide the first definitive detection of this component of the cometary ices. Interesting variations in the production of HCN were observed with time scales less than a day. Likewise, there appeared to be variations in the ratio of the hyperfine components of the J = 1-0 transition.

Irvine, W. M.↗
NASA NTRS1986

Studies of radiative transfer in planetary atmospheres

Schloerb and Claussen continued their analysis of the very high quality data set obtained on the 18 centimeter OH line from the Comet P/Halley with the NRAO 43 meter antenna. The high spectral resolution (0.22 km/sec) and high signal-to-noise of the OH spectra make them ideal for the study of kinematics in the coma. Synthetic profiles were initiated for comparison with the data. A vectorial model was developed using the Monte Carlo techniques originated by Combi and Delsemme. Analysis of the millimeter wavelength observations of HCN emission from P/Halley obtained throughout much of the recent apparition were continued using the University of Massachusetts 14 millimeter-wavelength (FCRAO) antenna. A detailed analysis of the HCN lineshpaes was performed over the last six months. The excitation of HCN in the coma was studied to obtain a detailed match to the observed spectra. The passive millimeter wave radiometer was used to probe the physical and chemical nature of comets from spacecraft. Work was continued on an improved theory of radiative transfer for rough and porous surfaces, such as the regoliths of satellites, asteroids, and comets.

Irvine, W. M.↗
NASA NTRS1987

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

Laboratory measurements were conducted to evaluate properties of atmospheric gases under simulated conditions for the outer planets. A significant addition to this effort was the capability to make such measurements at millimeter wavelengths. Measurements should soon be completed on the millimeter wave absorption from ammonia under Jovian conditions. Also studied will be the feasibility of measuring the microwave and millimeter wave properties of phosphine (PH3) under simulated Jovian conditions. Further analysis and application of the laboratory results to microwave and millimeter wave absorption data for the outer planet, such as Voyager Radio Occultation experiments, will be pursued.

Steffes, Paul G.↗
NASA NTRS1986

Impact erosion of planetary atmospheres

The amount of gas imparted to the atmosphere by an interaction of an impactor with a planet is estimated. The interaction of an impactor with a planet is described. The enthalpy of the gas, the kinetic energy of mass motion, and the evaporation of the impactor are examined. The properties of the shock-heated gas are calculated and analyzed. It is observed that the mass of atmospheric gas driven off into space by an impact is proportional to the mass of atmospheric gas encountered by the impactor.

Walker, James C. G.↗
NASA NTRS1986

Approximate methods for finding CO2 15-micron band transmission in planetary atmospheres

Physical band models that use simplifying assumptions about the structure of the CO2 15-micron band are described and compared with the accurate line-by-line model of Fels and Schwarzkopf (1981). The methods have application to the models of the atmospheres of Venus, earth, and Mars. The narrow-band methods include a general random model and techniques employing the Malkmus (1967) line-strength distribution, and the accuracy of these models at low pressure is found to be sensitive to the line-strength distribution and the line shape. When combined with a simple Voigt parameterization, the more efficient approximate methods represented by an exponential wideband model are found to be almost as accurate as the expensive narrow-band models. Empirical logarithmic wideband models used in climate-modeling studies are found to be very efficient, but of limited range of validity.

Crisp, David↗
NASA NTRS1988

Laboratory evaluation and application of microwave absorption properties under simulated conditions for planetary atmospheres

In the first half of this grant year, laboratory measurements were conducted on the millimeter-wave properties of atmospheric gases under simulated conditions for the outer planet. Significant improvements in the current system have made it possible to accurately characterize the opacity from gaseous NH3 at longer millimeter wavelengths (7 to 10 mm) under simulated Jovian conditions. In the second half of the grant year, it is hoped to extend such measurements to even shorter millimeter-wavelengths. Further analysis and application of the laboratory results to microwave and millimeter-wave absorption data for the outer planets, such as results from Voyager Radio Occultation experiments and earth-based radio astronomical observations will be continued. The analysis of available multispectral microwave opacity data from Venus, including data from the most recent radio astronomical ovservations in the 1.3 to 3.6 cm wavelength range and newly obtained Pioneer-Venus Radio Occulatation measurements at 13 cm, using the laboratory measurements as an interpretative tool will be pursued.

Steffes, Paul G.↗
NASA NTRS1987

Diode laser measurements of CO line widths at planetary atmospheric temperatures

A tunable diode laser spectrometer and the sweep integration technique were used to measure hydrogen-broadened half-widths and nitrogen-broadened half-widths of eight lines between P(1) and P(15) in the CO fundamental at several temperatures between 94 and 298 K. The results are of interest in connection with studies of the atmospheres of earth, Jupiter, Saturn, and Titan.

Varanasi, P.↗
NASA NTRS1987

Measurements on 4.7 micron CH3D lines broadened by H2 and N2 at temperatures relevant to planetary atmospheres

A tunable diode laser and the sweep integration technique were used to measure the absolute intensities, H2-broadened half-widths, and N2-broadened half-widths of P(5,2), P(5,3), P(7,2), P(7,3), and P(8,3) in the nu2-fundamental band of C-12H3D at several temperatures beteen 94 and 300 K. Results are of interest in connection with N2-broadened lines in the atmospheres of Titan and earth.

Chudamani, S.↗
NASA NTRS1988

Tunable solid-state lasers - An emerging technology for remote sensing of planetary atmospheres

The present development status and prospective (1990s) performance-improvement evaluation of tunable solid-state laser technology notes recent trends toward spectrum coverage over the 0.20-14.0 microns range, in addition to dramatic increases in efficiency, service life, and reliability. It is judged that the Ti:Al2O3 laser and the AgGaSe2 optical parametric oscillator pumped by a Ho:YAG laser could cover the near-IR and mid-IR regions of the spectrum. Laser diodes operating at 0.78 microns should provide an excellent pump for a Ho:YAG laser.

Barnes, Norman P.↗
NASA NTRS1988

A new approach to resonance line scattering in planetary atmospheres

The invariant imbedding technique is applied to the problem of resonance line scattering with frequency redistribution. By applying the principles of invariance to the resonance line scattering problem a set of non-linear, integrodifferential equations for the scattering and transmission functions are derived. Thus, an alternate approach to the resonance line scattering problem is presented. Rather than solving for the specific intensity directly the invariant imbedding equations may be solved for the scattering and transmission functions from which the specific intensity may be calculated. The technique is very general and in principle, can accommodate scattering in inhomogeneous atmospheres with arbitrary frequency redistribution and scattering phase functions. Solutions to the invariant imbedding equations in some simple cases are presented. If the scattering is isotropic and completely noncoherent and the atmosphere may be modeled as homogeneous, the scattering and transmission functions may be expressed in terms of generalized H, X and Y functions. This technique is extended to the problems of coupled spectral lines and scattering of radiation from internal sources.

Yelle, Roger V.↗
NASA NTRS1988

Studies of extended planetary atmospheres

Spectroscopic observations of gases and plasmas in the Jupiter system, and related phenomena such as the recently-discovered sodium atmospheres of Mercury and the Moon were made. Cunningham's work on Jupiter spectroscopy is complete. The optical thickness of the ammonia cloud increases from about 3 in the morning to 6 at sunset. This effect seems to be due to the combination of internal heat flow and a convective region heated at the top, giving strong convection at night and none during the day. Near-simultaneous methane data are of poor quality, but are consistent with this picture. Schneider's work on the sodium environment of Io is also complete. The eclipse data extend to nearly 10 Io radii and nicely match the densities in the outer regions (to 100 Io radii) obtained from the intensity scattered in the D lines. Other data show very fast jets of sodium (up to 100 km/sec), frequently tilted out of the orbital plane. Researchers seem to be seeing neutralized ions, not from the torus itself but from atmospheric sodium ionized and then quickly neutralized. The data set on Mercurian sodium has been augmented, and supplemented by IR reflectance spectra.

Hunten, Donald M.↗
NASA NTRS1989

Linewidth measurements in the thermal infrared bands of (C-12)H3D at planetary atmospheric temperatures

Collision-broadened halfwidths of three lines in the nu3 fundamental band and of four lines in the nu6 fundamental band of (C-12)H3D have been measured at temperatures between 123 and 295 K using the Doppler-limited spectral resolution of a tunable diode laser spectrometer. Temperature dependence of the linewidths has been determined in self-broadening and in broadening by H2, He and N2.

Varanasi, Prasad↗
NASA NTRS1989

Measurements of the D/H ratio in planetary atmospheres by ground based infrared spectroscopy

A systematic study of deuterium in the solar system using the molecules CH3D and HDO as tracers is carried out. For the outer solar system, ground-based spectra of Saturn, Uranus, Neptune and Titan in the region of CH3D absorptions near, 1.6 microns are obtained. The analyses of these spectra required extensive high-resolution laboratory studies of both CH4 and CH3D. For the terrestrial planets, the spectrum of Mars in the region of HDO absorption near 3.7 microns, is recorded. A similar study of Venus is underway. The values of D/H derived from these investigations are used to constrain models for the origin and evolution of the various atmospheres.

Debergh, C.↗
NASA NTRS1988

The photochemistry of planetary atmospheres

Recent theoretical and observational investigations of photochemical processes in the atmospheres of the planets and their satellites are reviewed. Particular attention is given to the CO2-dominated atmospheres of Mars and Venus, the hydrogen-dominated atmospheres of the Jovian planets, the SO2 atmosphere of Io, and the massive atmospheres of Titan and Triton. The principal reaction paths involved are listed and briefly characterized, and numerical data on atmospheric compositions are given in tables.

Dalgarno, A.↗
NASA NTRS1990

Study of planetary atmospheres by absorptive occultations

The absorption spectrum of the upper atmosphere can be observed as a function of height as a spacecraft observes the setting or rising of the sun or a star behind the limb of a planet. Data reduction methodology for absorptive occultations are described. Emphasis is placed on occultations by atmospheres other than the earth's in which the observed effects are dominated by absorption. Observations of the other planets by ultraviolet spectrometers able to look at the sun as well as stars are presented. Most of the instruments utilized the extreme ultraviolet wavelength region between 500 and 1600 A, which includes strong absorptions by nearly all gases and is consequently very useful for an initial exploration of a little known atmosphere. A closely related development is the utilization of stellar occultations seen from the earth's surface or airborne platforms, to obtain geometrical information on planets, rings, and asteroids, including density profiles of atmospheres. Voyager instruments defined the upper atmospheres of all four Jovian planets and the satellites Titan and Triton. Tight upper limits on the atmosphere of Mercury were established by Mariner 10.

Smith, Gerald R.↗