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At least 847 records · Page 47
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Mars Upper Atmospheric Temperature and Atomic Oxygen Density Derived from the O i 130.4 nm Emission Observed by NASA’s MAVEN Mission

The abundance of atomic oxygen is a major unknown for the Mars upper atmosphere, and systematic measurements of this key species is a primary objective of NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission. Moreover, the Martian dayside temperature structure and its variability has been a subject of considerable debate in the past. In this study, an inversion analysis of the periapsis limb scans of the O i 130.4 nm emission observed by MAVEN is performed to quantify the neutral temperature and atomic oxygen abundance in the Mars upper atmosphere. Our analysis yields unprecedented resolution of the spatial variation of Mars atomic oxygen, showing that its exobase density decreases with the solar zenith angle (SZA) from ∼0° to 60° by about an order of magnitude, from ∼10{sup 8} to ∼10{sup 7} cm{sup −3} near perihelion (2015 April) and from ∼10{sup 7} to ∼10{sup 6} cm{sup −3} near aphelion (2017 November). For a given SZA the exobase densities near perihelion are about an order of magnitude higher than those near aphelion. The [O]/[CO{sub 2}] mixing ratio at 130 km altitude can vary from ∼0.1% to 4.6%, which also decreases with increasing SZA. Moreover, it is shown that the Mars exobase temperature does not vary significantly with SZA from ∼0° to ∼60°, which is estimated to be ∼239.2 ± 27.6 K near perihelion and ∼162.4 ± 19.9 K near aphelion, with a difference of 76.8 K between these two seasonal extremes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

New evidence for solar cycle variations at great distances

Recent studies of solar planetary relationships are directed toward exploring how far out from the sun one could observe solar cycle variations. A positive solar Jovian relationship is suggested from a Chree superposed epoch study of the intensity of the great red spot of Jupiter over a period of about six solar cycles. The characteristic double maxima observed in the solar cycle variation is common to other observations of solar events in the photosphere, chromosphere, and corona; radio and corpuscular emissions from the sun; cosmic ray intensity and geomagnetic activity. The same method of analysis adopted for the study of luminosity changes of the planets Jupiter, Saturn, Uranus, and Neptune indicates that the fluctuations of luminosity follow the single maximum solar cycle represented by sunspot numbers. In conjunction with changes of upper atmospheric density and temperature, it is suggested that the extreme ultraviolet (EUV) emission from the sun may be connected with luminosity changes. A method of distinguishing between phenomena related to solar wind and those related to solar EUV is presented.

Venkatesan, D.↗
NASA NTRS1992

Paradigm lost: Venus crater depths and the role of gravity in crater modification

Previous to Magellan, a convincing case had been assembled that predicted that complex impact craters on Venus were considerably shallower than their counterparts on Mars, Mercury, the Moon, and perhaps even Earth. This was fueled primarily by the morphometric observation that, for a given diameter (D), crater depth (d) seems to scale inversely with surface gravity for the other planets in the inner solar system. The unpredicted depth of fresh impact craters on Venus argues against a simple inverse relationship between surface gravity and crater depth. Factors that could contribute to deep craters on Venus include (1) more efficient excavation on Venus, possibly reflecting rheological effects of the hot venusian environment; (2) more melting and efficient removal of melt from the crater cavity; and (3) enhanced ejection of material out of the crater, possibly as a result of entrainment in an atmosphere set in motion by the passage of the projectile. The broader issue raised by the venusian crater depths is whether surface gravity is the predominant influence on crater depths on any planet. While inverse gravity scaling of crater depths has been a useful paradigm in planetary cratering, the venusian data do not support this model and the terrestrial data are equivocal at best. The hypothesis that planetary gravity is the primary influence over crater depths and the paradigm that terrestrial craters are shallow should be reevaluated.

Sharpton, Virgil L.↗
NASA NTRS1993

First results from a laboratory facility for measurement of emission spectra under simulated planetary conditions

We have developed a laboratory spectroscopic facility for the measurement of emission spectra under simulated planetary conditions. Spectral measurements are made from 6 to 13 microns with a scanning grating monochromator equipped with a HgCdTl detector. An environment chamber in service in Hawaii for several years in which we can control the temperature from 77 K to 500 K, the pressure from 10(exp -5) torr to two atmospheres, has been equipped with a 77 K or 273 K cold shield. The shield serves to minimize light reflected off the sample and to aid in development of thermal gradients for obtaining spectra under conditions simulating the thermal environment of airless bodies. Samples are placed in small cups on a temperature controlled substrate allowing measurements of emission due to heating from below by the substrate, or from illumination from a solar simulation source.

Lucey, Paul G.↗
NASA NTRS1998

Overview of Future NASA Tether Applications

The groundwork has been laid for tether applications in space. NASA has developed tether technology for space applications since the 1960's. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (PMG, 1993). Various types of tethers and systems can be used for space transportation. Short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will demonstrate electrodynamic tether thrust during its flight in early 2000. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a higher orbit or a transfer orbit for lunar and planetary missions. Recently completed system studies of this concept indicate that it would be a relatively low-cost in-space asset with long-term multi-mission capability. Tethers can also be used to support space science by providing a mechanism for precision formation flying and for reaching regions of the upper atmosphere that were previously inaccessible.

Johnson, Les↗
NASA NTRS2023

Atmospheric Science Questions for a Uranian Probe

The Ice Giants represent a unique and relatively poorly characterized class of planets that have been largely unexplored since the brief Voyager 2 flyby in the late 1980’s. Uranus is particularly enigmatic, due to its extreme axial tilt, offset magnetic field, apparent low heat budget, mysteriously cool stratosphere and warm thermosphere, as well as a lack of well-defined, long-lived storm systems and distinct atmospheric features. All these characteristics make Uranus a scientifically intriguing target, particularly for missions able to complete in situ measurements. The 2023-2032 Decadal Strategy for Planetary Science and Astrobiology prioritized a flagship orbiter and probe to explore Uranus with the intent to “...transform our knowledge of Ice Giants in general and the Uranian system in particular” (National Academies of Sciences and Medicine, 2022). In support of this recommendation, we present community-supported science questions, key measurements, and a suggested instrument suite that focuses on the exploration and characterization of the Uranian atmosphere by an in situ probe. The scope of these science questions encompasses the origin, evolution, and current processes that shape the Uranian atmosphere, and in turn the Uranian system overall. Addressing these questions will inform vital new insights about Uranus, Ice Giants and Gas Giants in general, the large population of Neptune-sized exoplanets, and the Solar System as a whole.

Uranus↗
NASA NTRS1975

The structure and evolution of Jupiter - The fluid contraction stage

The complete evolution of a contracting star of Jovian mass consisting of a convective adiabatic homogeneous fluid is determined using stellar structure methods, improved model atmosphere calculations, and substantially improved thermodynamic properties for hydrogen and hydrogen-helium fluids. The model atmospheres are calculated in the form of time-averaged vertical temperature structures, including all relevant sources of opacity and a solar energy deposition component, and the thermodynamic properties are modified to obtain better agreement with Monte Carlo results for metallic fluids. The resultant gravitationally contracting evolutionary models are found to have two phases: an early stellar phase similar to a typical low-mass pre-main-sequence body and a later phase constituting an approach to a degenerate-dwarf cooling curve. The first phase is shown to have high luminosities and internal temperatures, while the second gives excellent agreement with the observed radius and luminosity of Jupiter. Analysis indicates that the equation of state and superadiabaticity have the strongest influence on evolution over planetary time scales.

Graboske, H. C., Jr.↗
NASA NTRS2009

Heliophysics: The Solar and Space Physics of a New Era. Recommended Roadmap for Science and Technology 2009-2030

Our planet is immersed in a seemingly invisible yet exotic and inherently dangerous environment. Above the protective cocoon of Earth's lower atmosphere is a plasma soup composed of electrified and magnetized matter entwined with penetrating radiation and energetic particles. The Earth's magnetic field interacts with the Sun's outer atmosphere to create this extraordinary environment.

Heliophysics↗
NASA NTRS1997

The early faint sun paradox: organic shielding of ultraviolet-labile greenhouse gases

Atmospheric mixing ratios of approximately 10(-5 +/- 1) for ammonia on the early Earth would have been sufficient, through the resulting greenhouse warming, to counteract the temperature effects of the faint early sun. One argument against such model atmospheres has been the short time scale for ammonia photodissociation by solar ultraviolet light. Here it is shown that ultraviolet absorption by steady-state amounts of high-altitude organic solids produced from methane photolysis may have shielded ammonia sufficiently that ammonia resupply rates were able to maintain surface temperatures above freezing.

Non-NASA Center↗
DOE OSTI2020

White dwarf pollution by hydrated planetary remnants: hydrogen and metals in WD J204713.76–125908.9

ABSTRACT WD J204713.76–125908.9 is a new addition to the small class of white dwarfs with helium-dominated photospheres that exhibit strong Balmer absorption lines and atmospheric metal pollution. The exceptional abundances of hydrogen observed in these stars may be the result of accretion of water-rich rocky bodies. We obtained far-ultraviolet and optical spectroscopy of WD J204713.76–125908.9 using the Cosmic Origin Spectrograph on-board the Hubble Space Telescope and X-shooter on the Very Large Telescope, and identify photospheric absorption lines of nine metals: C, O, Mg, Si, P, S, Ca, Fe, and Ni. The abundance ratios are consistent with the steady-state accretion of exo-planetesimal debris rich in the volatile elements carbon and oxygen, and the transitional element sulphur, by factors of 17, 2, and 4, respectively, compared to the bulk Earth. The parent body has a composition akin to Solar system carbonaceous chondrites, and the inferred minimum mass, 1.6 × 1020 g, is comparable to an asteroid 23 km in radius. We model the composition of the disrupted parent body, finding from our simulations a median water mass fraction of 8 per cent.

Hoskin, Matthew J.↗
NASA NTRS2001

Solid-State Power Generating Microdevices for Distributed Space System Architectures

Deep space missions have a strong need for compact, high power density, reliable and long life electrical power generation and storage under extreme temperature conditions. Conventional power generating devices become inefficient at very low temperatures (temperatures lower than 200 K encountered during Mars missions for example) and rechargeable energy storage devices cannot be operated thereby limiting mission duration. At elevated temperatures (for example for planned solar probe or Venus lander missions), thin film interdiffusion destroys electronic devices used for generating and storing power. Solar power generation strongly depends upon the light intensity, which falls rapidly in deep interplanetary missions (beyond 5 AU), and in planetary missions in the sun shadow or in dusty environments (Mars, for example). Radioisotope thermoelectric generators (RTGs) have been successfully used for a number of deep space missions RTGs. However, their energy conversion efficiency and specific power characteristics are quite low, and this technology has been limited to relatively large systems (more than 100 W). The National Aeronautics and Space Administration (NASA) and the Jet Propulsion Laboratory (JPL) have been planning the use of much smaller spacecrafts that will incorporate a variety of microdevices and miniature vehicles such as microdetectors, microsensors, and microrovers. Except for electrochemical batteries and solar cells, there are currently no available miniaturized power sources. Novel technologies that will function reliably over a long duration mission (ten years and over), in harsh environments (temperature, pressure, and atmosphere) must be developed to enable the success of future space missions. It is also expected that such micropower sources could have a wide range of terrestrial applications, in particular when the limited lifetime and environmental limitations of batteries are key factors. Additional information is contained in the original extended abstract.

Fleurial, J.-P.↗
NASA NTRS2005

Lunar and Planetary Science XXXVI, Part 5

Topics discussed include: Automation Recognition oF Crater-Like Structures in Terrestrial and Plantary Images; Condensation from Cluster-IDP Enriched Vapor Inside the Snow Line: Implications for Mercury, Asteroids, and Enstatite Chondrites; Tomographic Location of Potential Melt-Bearing Phenocrysts in Lunar Glass Spherules; Source and Evolution of Vapor Due to Impacts into Layered Carbonates and Silicates; Noble Gases and I-Xe Ages of the Zag Meteorite; The MArs Hand Lens Imager (MAHLI) for the 209 Mars Science Laboratory; The Sedimentary Rocks of Meridiani Planum, in Context; Three-System Isotopic of Lunar Norite 78238: Rb-Sr Results; Constraints on the Role of Curium-247 as a Source of Fission Xenon in the Early Solar System; New Features in the ADS Abstract Service; Cassini RADAR's First Look at Titan; Volcanism and Volatile Recycling on Venus from Lithospheric Delamination; The Fate of Water in the Martian Magma Ocean and the Formation of an Early Atmosphere; Mars Odyssey Neutron Spectrometer Water-Equivalent Hydrogen: Comparison with Glacial; Landforms on Tharsis; Using Models of Permanent Shadow to Constrain Lunar Polar Water Ice Abundances; Martian Radiative Transfer Modeling Using the Optimal Spectral Sampling Method; Petrological and Geochemical Consideration on the Tuserkanite Meteorite; and Mineralogy of Asteroids from Observations with the Spitzer Space Telescope.

Source record↗
NASA NTRS1984

The Planetary Observer Program

An overview is presented of NASA's plans for the Planetary Observer Program, whose key element is to control the cost of each mission while establishing a long-term, stable base for the planetary sciences. The SSEC (Solar System Exploration Committee) has endorsed the view that many high science priority inner solar system missions are possible through the use of spacecraft derived from existing earth-orbital spacecraft. It has also recommended the application of space hardware such as that used on the Voyager and Galileo missions, development of both a new modular spacecraft for outer planet, comet, and main-belt asteroid missions (Mariner Mark II Program), and a multi-mission operations system to support future missions after the Venus Radar Mapper (VRM), and Galileo. A set of missions for the SSEC's Core Program has been recommended; they include: the VRM, the Mars Geoscience/Climatology Observer, the Comet Rendezvous/Asteroid Flyby, the Lunar Geoscience Orbiter, the Near-Earth Asteroid Rendezvous, the Venus Atmosphere Probe, the Mars Aeronomy Orbiter, the Mars Surface Probe, and the Comet Intercept Sample Return.

Blume, W. H.↗
NASA NTRS2004

Atmospheric Trace Gas Abundances and Stable Isotope Ratios via IR-LIF

We propose to develop new technologies with support provided by PIDDP that will enable the in situ measurements of abundances and stable isotope ratios in important radiatively and biogenically active gases such as carbon dioxide, carbon monoxide, water, methane, nitrous oxide, and hydrogen sulfide to very high precision (0.1 per mil or better for the isotopic ratios, for example). Such measurements, impossible at present, could provide pivotal new constraints on the global (bio)geochemical budgets of these critical species, and could also be used to examine the dynamics of atmospheric transport on Mars, Titan, and other solar system bodies. We believe the combination of solid state light sources with imaging of the IR laser induced fluorescence (IR-LIF) via newly available detector arrays will make such in situ measurements possible for the first time. Even under ambient terrestrial conditions, the LIF yield from vibrational excitation of species such as water and carbon dioxide should produce emission measures well in excess of ten billion photons/sec from samples volumes of order 1 c.c. These count rates can, in principle, yield detection limits into the sub-ppt range that are required for the in situ isotopic study of atmospheric trace gases. While promising, such technologies are relatively immature, but developing rapidly, and there are a great many uncertainties regarding their applicability to in situ IR-LIF planetary studies. We therefore feel PIDDP support will be critical to developing these new tools, and propose a three-year program to combine microchip near-IR lasers with low background detection axes and state-of-the-art HgCdTe detectors developed for astronomical spectroscopy to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions.

Blake, Geoffrey A.↗
NASA NTRS1981

Equatorial superrotation in a thermally driven zonally symmetric circulation

Near the equator where the Coriolis force vanishes, the momentum balance for the axially symmetric circulation is established between horizontal and vertical diffusion, which, a priori, does not impose constraints on the direction or magnitude of the zonal winds. Solar radiation absorbed at low latitudes is a major force in driving large scale motions with air rising near the equator and falling at higher latitudes. In the upper leg of the meridional cell, angular momentum is redistributed so that the atmosphere tends to subrotate (or corotate) at low latitudes and superrotate at high latitudes. In the lower leg, however, the process is reversed and produces a tendency for the equatorial region to superrotate. The outcome depends on the energy budget which is closely coupled to the momentum budget through the thermal wind equation; a pressure (temperature) maximum is required to sustain equatorial superrotation. Such a condition arises in regions which are convectively unstable and the temperature lapse rate is superadiabatic. It should arise in the tropospheres of Jupiter and Saturn; planetary energy from the interior is carried to higher altitudes where radiation to space becomes important. Upward equatorial motions in the direct and indirect circulations (Ferrel-Thomson type) imposed by insolation can then trap dynamic energy for equatorial heating which can sustain the superrotation of the equatorial region.

Mayr, H. G.↗
NASA NTRS1978

Multiple Discipline science assessment

Various science disciplines were examined to determine where and when it is appropriate to include their objectives in the planning of planetary missions. The disciplines considered are solar astronomy, stellar and galactic astronomy, solar physics, cosmology and gravitational physics, the geosciences and the applied sciences. For each discipline, science objectives are identified which could provide a multiple discipline opportunity utilizing either a single spacecraft or two spacecraft delivered by a single launch vehicle. Opportunities using a common engineering system are also considered. The most promising opportunities identified include observations of solar images and relativistic effects using the Mercury orbiter; collection of samples exposed to solar radiation using the Mars surface sample return; studies of interstellar neutral H and He, magnetic fields, cosmic rays, and solar physics during Pluto or Neptune flybys; using the Mars orbiter to obtain solar images from 0.2 AU synchronous or from 90 deg orbit; and the study of the structure and composition of the atmosphere using atmospheric probes and remotely piloted vehicles.

Wells, W. C.↗
NASA NTRS1984

Jovian magnetospheric neutral wind and auroral precipitation flux

A theoretical model of the Jovian magnetosphere is used to describe the mechanism by which energy is transported from Jupiter's rotation into heavy ions precipitating into the atmosphere, and resulting in intense ultraviolet aurora. The flow and magnetic field configurations used in the model are drawn from data collected by the Voyager orbiter. It is shown that the observed Jovian auroral radiation power is supplied by the precipitation of heavy ions of Iogenic origin. The ions are created by a charge exchange between the Io torus and fly as neutrals to the outer magnetosphere. A small fraction of the ions are photoionized in the outer magnetosphere where they acquire a magnetic moment determined by the local corotation electric field and planetary magnetic field. As the ions diffuse inward they are energized adiabatically. A schematic drawing illustrating the evolution of this process is provided. It is also shown that Jupiter may be a significant source of heavy ions for the solar wind by means of photoionization of a neutral wind. Secondary charge exchange in the outer magnetosphere could supply a flux of minimum energy neutral atoms that may have been measured by the Voyager Low Energy Charged Particle detector (LECP).

Eviatar, A.↗
NASA NTRS1993

Global variations of zonal mean ozone during stratospheric warming events

Eight years of Solar Backscatter Ultraviolet (SBUV) ozone data are examined to study zonal mean variations associated with stratospheric planetary wave (warming) events. These fluctuations are found to be nearly global in extent, with relatively large variations in the tropics, and coherent signatures reaching up to 50 deg in the opposite (summer) hemisphere. These ozone variations are a manifestation of the global circulation cells associated with stratospheric warming events; the ozone responds dynamically in the lower stratosphere to transport, and photochemically in the upper stratosphere to the circulation-induced temperature changes. The observed ozone variations in the tropics are of particular interest because transport is dominated by zonal-mean vertical motions (eddy flux divergences and mean meridional transports are negligible), and hence, substantial simplifications to the governing equations occur. The response of the atmosphere to these impulsive circulation changes provides a situation for robust estimates of the ozone-temperature sensitivity in the upper stratosphere.

Randel, William J.↗