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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Studies of Tenuous Planetary Atmospheres

In order to understand the physical and chemical processes which produce the tenuous planetary and planetary satellite (upper) atmospheres through interactions with their particle, field, and radiation environs, it is necessary to analyze remotely observed and spacecraft data with physically meaningful models. With this in mind, we have undertaken a coupled program of theoretical modeling and complementary data analysis regarding the global distributions of neutral and ionized gases in, and escape from, tenuous planetary atmospheres of Io and Europa. The theoretical models developed will have further applications to other tenuous atmospheres such as that of Pluto and Titan or the upper atmospheres of the terrestrial planets.

Combi, Michael R.↗
NASA NTRS1979

Implications of the gas compositional measurements of Pioneer Venus for the origin of planetary atmospheres

Comparisons are made between the volatile inventories of the terrestrial planets, including Pioneer Venus data, and the predictions of three classes of theories for the origin of planetary atmospheres. Serious difficulties arise for the primary atmosphere and external source hypotheses. The grain accretion hypothesis can account for the trends in the volatile inventory from Venus to earth to Mars, if volatiles were incorporated into planet-forming grains at nearly the same temperature for all of these planets, but at systematically lower pressures in the regions of planet formation farther from the center of the solar nebula.

Pollack, J. B.↗
NASA NTRS1998

Cross Sections for Electron Impact Excitation of Ions Relevant to Planetary Atmospheres Observation

The goal of this research grant was to calculate accurate oscillator strengths and electron collisional excitation strengths for inelastic transitions in atomic species of relevance to Planetary Atmospheres. Large scale configuration-interaction atomic structure calculations have been performed to obtain oscillator strengths and transition probabilities for transitions among the fine-structure levels and R-matrix method has been used in the calculations of electron-ion collision cross sections of C II, S I, S II, S III, and Ar II. A number of strong features due to ions of sulfur have been detected in the spectra of Jupiter satellite Io. The electron excitation cross sections for the C II and S II transitions are studied in collaboration with the experimental atomic physics group at the Jet Propulsion Laboratory. There is excellent agreement between experiment and theory which provide an accurate and broad-base test of the ability of theoretical methods used in the calculation of atomic processes. Specifically, research problems have been investigated for: electron impact excitation cross sections of C II: electron impact excitation cross sections of S III; energy levels and oscillator strengths for transitions in S III; collision strengths for electron collisional excitation of S II; electron impact excitation of inelastic transitions in Ar II; oscillator strengths of fine-structure transitions in neutral sulfur; cross sections for inelastic scattering of electrons from atomic nitrogen; and excitation of atomic ions by electron impact.

Tayal, Swaraj S.↗
NASA NTRS2020

Interpreting Exo-Planetary Atmospheres with the Next Generation Space-Based Telescope

We will soon have the technological capability to measure the atmospheric composition of temperate Earth-sized planets orbiting nearby stars. Interpreting these atmospheric signals poses a new challenge to planetary science. In contrast to jovian-like atmospheres, whose bulk compositions consist of hydrogen and helium, terrestrial planet atmospheres are likely comprised of high mean molecular weight secondary atmospheres, which have gone through a high degree of evolution. In order to understand the processes which affect a planetary atmosphere, I use early Mars as a case study. I leverage a combination of one-dimensional climate, photochemical and energy balance models in order to create one self-consistent model that closely matches currently available climate data. However, unlike in-situ observations from our own solar system, remote sensing techniques need to be developed and understood in order to accurately characterize exo-atmospheres. I describe the models used to create synthetic transit transmission observations, which includes models of transit spectroscopy and instrumental noise. Using these, I lay the framework for an information content-based approach to optimize our observations and maximize the retrievable information from exo-atmospheres. First I test the method on observing strategies of the well-studied, low-mean-molecular weight atmospheres of warm-Neptunes and hot Jupiters. Upon verifying the methodology, I finally address optimal observing strategies for temperate, high-mean-molecular weight atmospheres (Earths/super-Earths).

Batalha, Natasha↗
NASA NTRS1972

Problem of photochemical equilibrium of ozone in planetary atmospheres: Ozone distribution in the lower atmosphere of Mars

The inherent errors of applying terrestrial atmospheric ozone distribution studies to the atmosphere of other planets are discussed. Limitations associated with some of the earlier treatments of photochemical equilibrium distributions of ozone in planetary atmospheres are described. A technique having more universal application is presented. Ozone concentration profiles for the Martian atmosphere based on the results of the Mariner 4 radio occultation experiment and the more recent results with Mariner 6 and Mariner 7 have been calculated using this approach.

Grams, G. W.↗
NASA NTRS1980

Radio scintillations during occultations by turbulent planetary atmospheres

The radio occultation experiment which uses the radio link between the earth and spacecraft passing behind planets has proven to be an important method for remote sensing turbulence in planetary atmospheres. The effects of defocusing and anisotropic irregularities on the turbulence-induced fluctuations of the radio occultation signal are examined. Rytov's method along with geometrical optics is employed to study the frequency spectra and coherences of the log amplitude and phase fluctuations of spherical waves operating at one as well as two frequencies. Comparison with the Mariner 5 2.3-GHz measurements shows good agreement with the theoretical results.

Woo, R.↗
NASA NTRS1990

A laboratory investigation of the production and properties of molecular and radical species pertinent to planetary atmospheres

Vinylidene (H2C=C) is shown to be the largest photodecomposition channel in the direct photolysis of both C2H2 and C2H4. The chemistry of H2C=C as it relates to planetary atmospheres is discussed. The vinyl radical (C2H3), important in the acetylene chemistry cycle, has been directly observed spectroscopically and the kinetics of several key reactions of this species measured.

Fahr, Askar↗
NASA NTRS2006

Analytic evaluation of the weighting functions for remote sensing of blackbody planetary atmospheres : the case of limb viewing geometry

In a recent publication (Ustinov, 2002), we proposed an analytic approach to evaluation of radiative and geophysical weighting functions for remote sensing of a blackbody planetary atmosphere, based on general linearization approach applied to the case of nadir viewing geometry. In this presentation, the general linearization approach is applied to the limb viewing geometry. The expressions, similar to those obtained in (Ustinov, 2002), are obtained for weighting functions with respect to the distance along the line of sight. Further on, these expressions are converted to the expressions for weighting functions with respect to the vertical coordinate in the atmosphere. Finally, the numerical representation of weighting functions in the form of matrices of partial derivatives of grid limb radiances with respect to the grid values of atmospheric parameters is used for a convolution with the finite field of view of the instrument.

remote sensing↗
NASA NTRS1978

Effects of the inhomogeneous background on radiation propagating through turbulent planetary atmospheres

Weak scattering, wave optics results are given for the first-order log-amplitude and phase, and for the second-order phase and angle of arrival, of radiation propagating through a turbulent planetary atmosphere. The analytical results include the effects of coupling to the inhomogeneous background upon which the turbulence is superimposed. Such coupling significantly affects signal characteristics in stellar and spacecraft occultation experiments, in contrast to situations involving much shorter paths, as in terrestrial propagation experiments.

Haugstad, B. S.↗
NASA NTRS1990

Microwave spectra of van der Waals complexes of importance in planetary atmospheres

The Fourier-transform Fabry-Perot pulsed-molecular-beam microwave spectrometer at NIST was used to study the microwave spectra of a number of molecular dimers and trimers that may be present in planetary atmospheres. The weak van der Waals bonds associated with these species usually give rise to rotational-tunneling splittings in the microwave spectra. The microwave spectrum of the water dimer species was used to illustrate the complications that can arise in the study of the rotational spectra of these loosely bound species. In addition to the water dimer species, the microwave spectra of the following hydrogen-bonded and van der Waals complexes were studied: (CO2)2-H2O, CO2-(H2O)2, CO2-H2S, N2-H2O, CO-H2O, SO2-H2O, and O3-H2O.

Suenram, R. D.↗
NASA NTRS2016

Computing Highly Accurate Spectroscopic Line Lists for Characterization of Planetary Atmospheres: CO2 and SO2 Line Lists Needed for Modeling Venus

Over the last decade, it has become apparent that the most effective approach for determining highly accurate rotational and rovibrational line lists for molecules of interest in planetary atmospheres and other astrophysical environments is through a combination of highresolution laboratory experiments coupled with state-of-the art ab initio quantum chemistry methods. The approach involves computing the most accurate potential energy surface (PES) possible using state-of-the art electronic structure methods, followed by computing rotational and rovibrational energy levels using an exact variational method to solve the nuclear Schrödinger equation. Then, reliable experimental data from high-resolution experiments is used to refine the ab initio PES in order to improve the accuracy of the computed energy levels and transition energies. From the refinement step, we have been able to achieve an accuracy of approximately 0.015 cm-1 for rovibrational transition energies, and even better for purely rotational transitions. This combined "experiment / theory" approach allows for determination of essentially a complete line list, with hundreds of millions of transitions, and having the transition energies and intensities be highly accurate. Our group has successfully applied this approach to determine highly accurate line lists for NH3, CO2 and isotopologues, and SO2 and isotopologues. Here I will report our latest results for CO2 and SO2 including all isotopologues. Comparisons to the available data in HITRAN2012 and other available databases will be shown, though we note that our line lists for SO2 are significantly more complete than any other databases. Since it is important to span a large temperature range in order to model the spectral signature of Venus as well as exoplanets, we will demonstrate how the spectra change on going from low temperatures (100 K) to higher temperatures (500 K to 1500 K).

potential energy surface (PES)5405 PLANETARY SCIEN↗
NASA NTRS1983

Planetary atmospheres

During the period from 1979 to 1982, Pioneer and Voyager missions to Venus, Jupiter, and Saturn combined with ongoing analysis and data collection from the Viking-Mars mission have contributed greatly to an understanding of planetary atmospheres. Research concerning the atmosphere of Venus is discussed, taking into account the atmospheric composition, the isotopic ratios of noble gases, data concerning temperature and pressure, information regarding various atmospheric layers, atmospheric density data, and models regarding the dynamical properties of Venus' atmosphere. Information concerning the atmosphere of Mars is also examined. Isotopic ratios of carbon and oxygen are considered along with altitude profiles, diurnal heating and cooling, and thermal tides and their relationship to dust storms. Attention is given to the temperature structure of the Jovian atmosphere, the morphology of Jovian cloud features, features in the Saturnian atmosphere, information with respect to the atmosphere of Titan, the rotation rates of Uranus, masses and densities of Uranus and Neptune, and the identification of Pluto as a small icy body.

Beebe, R.↗
NASA NTRS1993

A survey of bimolecular ion-molecule reactions for use in modeling the chemistry of planetary atmospheres, cometary comae, and interstellar clouds - 1993 supplement

This is a supplement to a previous paper (Anicich & Huntress 1986). It is a survey of bimolecular positive ion-molecule reactions with potential importance to the chemistry of planetary atmospheres, cometary comae, and interstellar clouds. This supplement covers the literature from 1986 through 1991, with some additional citations missed in the original survey. Over 200 new citations are included. A table of reactions is listed by reactant ion, and cross-references are provided for both ionic and neutral reactants and also for both ionic and neutral products.

Anicich, V. G.↗
NASA NTRS1982

Noble gases in planetary atmospheres - Implications for the origin and evolution of atmospheres

The radiogenic and primordial noble gas contents of the Venus, earth, and Mars atmospheres are compared with one another and with the noble gas content of other extraterrestrial samples, particularly meteorites. Key trends in the primordial noble gas content of terrestrial planetary atmospheres are shown to include: (1) a several-orders-of-magnitude decrease in Ne-20 and Ar-36 from Venus to earth to Mars; (2) a nearly constant Ne-20/Ar-36 ratio, which is comparable to that found in the more primitive carbonaceous chondrites and which is two orders of magnitude smaller than the solar ratio; (3) a sizable fractionation of Ar, Kr, and Xe from their solar ratios, though the degree of fractionation (especially for Ar-36/Xe-132) appears to decrease systematically from carbonaceous chondrites to Mars to earth to Venus; and (4) large differences in Ne and Xe isotopic ratios among earth, meteorites, and the sun. It is suggested that the grain-accretion hypothesis can explain all four trends, though the assumptions needed to achieve this agreement are far from proven.

Pollack, J. B.↗
NASA NTRS1986

A survey of bimolecular ion-molecule reactions for use in modeling the chemistry of planetary atmospheres, cometary comae, and interstellar clouds

All bimolecular positive ion-molecule reactions reported from 1965 to 1985 for temperatures below 1000 K are included in the present survey of those ion-molecule reactions pertinent to the chemistries of planetary atmospheres, cometary comae, and interstellar clouds. This survey is intended as an update of the first, by Huntress (1977). The tabular presentation is organized according to reactant ion, with cross-references for both the ionic and the neutral reactants as well as the ionic and neutral products.

Anicich, V. G.↗
NASA NTRS1962

One-Dimensional Heat Conduction Through the Skin of a Vehicle upon Entering a Planetary Atmosphere at Constant Velocity and Entry Angle

Closed-form solutions of the one-dimensional heat-conduction equations for the flow of heat into a plate with a laminar boundary layer have been obtained for a configuration entering a planetary atmosphere with constant velocity and negative entry angle. The atmospheric density was assumed to obey an exponential law and the temperature was assumed constant initially. The solution is in the form of a Fourier series expansion which, for most practical applications, can be approximated by retaining only one term of the expression. The solution applies to the initial part of the entry before the maximum heating conditions are encountered.

SKIN TEMPERATURE↗
NASA NTRS1990

Infrared line parameters at low temperatures relevant to planetary atmospheres

Employing the techniques that were described in several publications for measuring infrared lineshifts, linewidths and line intensities with a tunable diode laser, these parameters were measures for lines in the important infrared bands of several molecules of interest to the planetary astronomer at low temperatures that are relevant to planetary atmospheres using He, Ne, Ar, H2, N2, O2, and air as the perturbers. In addition to obtaining the many original data on the temperature dependence of the intensities and linewidths, it was also the first measurement of the same for the collision-induced lineshift of an infrared line and it showed that it was markedly different from that of the corresponding collision-broadened linewidth.

Varanasi, Prasad↗