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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Satellite formation. II

A satellite formation model is extended to include evolution of planetary ring material and elliptic orbital motion. In this model the formation of the moon begins at a later time in the growth of the earth, and a significant fraction of the lunar material is processed through a circumterrestrial debris cloud where volatiles might have been lost. Thus, the chemical differences between the earth and moon are more plausibly accounted for. Satellites of the outer planets probably formed in large numbers throughout the growth of those planets. Because of rapid inward evolution of the orbits of small satellites, the present satellite systems represent only satellites formed in the last few percent of the growths of their primaries. The rings of Saturn and Uranus are most plausibly explained as the debris of satellites disrupted within the Roche limit. Because such a ring would collapse onto the planet in the course of any significant further accretion by the planet, the rings must have formed very near or even after the conclusion of accretion.

Harris, A. W.↗
NASA NTRS2002

Four Station Interferometric Radar Observations of Mars

Planetary targets have been observed with radar since the late 1950s when it was first used for ranging experiments with the Moon. As telescope size and power increased, it became possible to observe more distant targets (Venus, Mars, and the outer satellites). Inherent to radar observations is the uncertainty as to the source of the reflection, there being two points where range and Doppler rings intersect on a sphere. The use of interferometric methods, first used on the moon with two stations and later on Venus and Mars, solved this problem. We extend the method through the addition of a fourth receiving telescope (thus doubling the number of projected baselines) and integration of the newly available Mars Orbiter Laser Altimeter (MOLA) topographic datasets.

Larsen, K. W.↗
NASA NTRS1989

Voyager at Neptune: 1989

The Voyager mission has taken advantage of a rare planetary alignment that occurs at intervals of about 175 years and affords an extraordinary opportunity: a grand tour by a single spacecraft of the outer planets Jupiter, Saturn, Uranus, and Neptune. Voyager 2 will fly past Nepture and its large moon Triton on August 24, 1989. The discovery of Neptune, along with its current history is discussed. The imaging challenges, tracking and data acquisition, and the Voyager spacecraft are explained. Data will be gathered on the ring arcs of Neptune, the atmosphere and surface of Neptune, Triton, and Nereid (the smaller moon).

Source record↗
NASA NTRS1989

Uranus - Beneath that bland exterior

Findings made by the Voyager missions regarding the atmosphere, magnetic field, rings, and satellites of Uranus are reviewed. The reasons for the bland appearance of the planet are addressed, and the use of radio and infrared instruments to determine the rotational speeds of the planet and atmosphere, the equatorial radius, and the atmospheric temperature is discussed. The corkscrew magnetic field and the dark, almost dust-free rings are described. The most significant features of the largest Uranian moons are mentioned.

Simpson, Richard A.↗
NASA NTRS1992

Planetary geosciences, 1989-1990

NASA's Planetary Geosciences Programs (the Planetary Geology and Geophysics and the Planetary Material and Geochemistry Programs) provide support and an organizational framework for scientific research on solid bodies of the solar system. These research and analysis programs support scientific research aimed at increasing our understanding of the physical, chemical, and dynamic nature of the solid bodies of the solar system: the Moon, the terrestrial planets, the satellites of the outer planets, the rings, the asteroids, and the comets. This research is conducted using a variety of methods: laboratory experiments, theoretical approaches, data analysis, and Earth analog techniques. Through research supported by these programs, we are expanding our understanding of the origin and evolution of the solar system. This document is intended to provide an overview of the more significant scientific findings and discoveries made this year by scientists supported by the Planetary Geosciences Program. To a large degree, these results and discoveries are the measure of success of the programs.

Zuber, Maria T.↗
NASA NTRS1994

A revised analysis of micron-sized particles detected near Saturn by the Voyager 2 plasma wave instrument

The impulsive noise that the plasma wave and radio astronomy instruments detected during the Voyager 2 swing by Saturn was attributed to dust grains striking the spacecraft. This report presents a reanalysis of the dust impacts recorded by the plasma wave instrument using an improved model for the response of the electric antenna to dust impacts. The fundamental assumption used in this analysis is that the voltage induced on the antenna is proportional to the mass of the impacting grain. Using the above assumption and the antenna response constants used at Uranus and Neptune, the following conclusions can be reached. The primary dust distribution consists of a 'disk' of particles that coincides with the equator plane and has a north-south thickness of 2-Delta zeta = 962 km. A less dense 'halo' with a north-south thickness of 2-Delta zeta = 3376 km surrounds the primary distribution. The dust particle sizes are of the order of 10 microns, assuming a mass density of 1 g/cu cm. The corresponding particle masses are of the order of 10(exp -9) g, and maximum number densities are of the order of 10(exp -2)/cu m. Most likely, the G ring is the dominate source since the particles were observed very close to that ring, namely at 2.86 R(sub S). Other sources, like nearby moons, are not ruled out especially when perturbations due to electromagnetic forces are included. The calculated optical depth differs by about a factor of 2 from photometric studies. The current particle masses, radii, and the effective north-south thickness of the particle distribution are larger than what Gurnett et al. (1983) reported by about 2, 1, and 1 orders of magnitude, respectively. This is attributed to the fact that the collection coefficient used in this study is smaller than what was used in Gurnett et al.'s earlier publication.

Tsintikidis, D.↗
NASA NTRS2012

Ringing After a High-Energy Collision: Ambipolar Oscillations During Impact Plasma Expansion

High-velocity impacts on the Moon and other airless bodies deliver energy and material to the lunar surface and exosphere. The target and i mpactor material may become vaporized and ionized to form a collision al plasma that expands outward and eventually becomes collisionless. In the present work, kinetic simulations of the later collision less stage of impact plasma expansion are performed. Attention is paid to characterizing "ambipolar oscillations" in which thermodynamic distur bances propagate outward to generate "ringing" within the expanding e lectron cloud, which could radiate an electromagnetic signature of lo cal plasma conditions. The process is not unlike a beam-plasma intera ction, with the perturbing electron population in the present case ac ting as a highly thermal "beam" that resonates along the expanding de nsity gradient. Understanding the electromagnetic aspects of impact p lasma expansion could provide insight into the lasting effects of nat ural, impact-generated currents on airless surfaces and charging haza rds to human exploration infrastructure and instrumentation.

Zimmerman, M. I.↗
NASA NTRS1993

Working group for planetary system nomenclature

Most of the activity of the Working Group and Task Group of the IAU during these three years has been centered on the nomenclature of Neptune's satellites and rings as revealed by the Voyager spacecraft. The emphasis is now shifting to Venus, in preparation for the detailed radar mapping of that planet begun by the Magellan spacecraft in August 1990. Approval has been asked for nomenclature of the Earth's moon, Venus, Mars, and Triton features as well as 4 other Neptune satellites and three Neptune rings.

Source record↗
DOE OSTI2024

Haasttse‐baad Tessera Ring Complex: A Valhalla‐Type Impact Structure on Venus?

Abstract Venus preserves ∼1,000 impact craters, yet to date no impact basins larger than 300 km in diameter—common in the oldest terrains on Mercury, Mars and the Moon—are recognized on Venus. The tessera terrain is Venus' oldest recognized terrain. We describe a ∼1,500 km‐diameter concentric ring‐graben complex preserved on Haasttse‐baad Tessera, Venus that we identify as the Haasttse‐baad Tessera Ring Complex (HTRC). Based on geologic relations and numerical modeling, we propose that the HTRC may represent a Valhalla‐type multiring impact basin formed late during the evolution of its host ribbon‐tessera terrain (rtt). Formation of Valhalla‐type impact basins could involve a unique three‐layer target rheology with a thin elastic layer above a low viscosity layer above a deep strong layer. This multi‐layer rheological sandwich is consistent with crustal rheology previously proposed for the formation of Venus' rtt. If the HTRC is a Valhalla‐type impact basin, it would be Venus' oldest, and currently largest, impact structure, providing a rare window into Venus' ancient past and with implications for early crustal processes on Venus.

58 GEOSCIENCES↗
NASA NTRS1978

Physical properties of the planets and satellites from radar observations

The radar cross section of a planetary target is defined as the area of an isotropic scatterer, normal to the illumination, that would yield the observed echo intensity, if it were placed at the target's location. Attention is given to the angular scattering law, surface imagery, and topography. The observational results are discussed, taking into account the moon and the inner planets, the asteroids, the Galilean satellites, and the rings of Saturn. It is pointed out that the reach of radar astronomy has maintained nearly an exponential growth over the past three decades, as the sensitivity of available radar systems has on average more than doubled each year. There are, however, limits to this growth set by the large costs required for a new generation of observing facilities. Only modest increases in radar system sensitivity are, therefore, expected for the next decade.

Pettengill, G. H.↗
NASA NTRS1979

Stellar occultation studies of the solar system

The paper covers the principles, observational procedures, and results relating to occultations of stars by solar system bodies other than the moon. Physical processes involved in occultations are presented including (1) extinction by ring material, (2) differential refraction by a planetary atmosphere, (3) extinction by a planetary atmosphere, and (4) Fresnel diffraction by sharp edges. It is noted that from a sufficient number of immersion and emersion timings of a stellar occultation, the radius and ellipticity of the occulting body can be accurately determined. From an occultation by a planet having an atmosphere, temperature, pressure, and number density profiles can be obtained along with information about the composition of the atmosphere and the extinction.

Elliot, J. L.↗
NASA NTRS1972

Comments on lunar origin.

Consideration of the tidal evolution of the earth-moon system in the light of recent published studies of lunar origin. The subjects include the factors of orbital evolution, the auxiliary Model Zero, orbital evolution along the outgoing branch, capture models, capture probability, capture with break-up, the tidal evolution of circular and elliptical fragmented rings, and precession and collisions in a ring of fragments. A numerical integration of precessions is performed for the actual nonzero mass of the moon and for a lunar distance of about 22 earth radii. A simplified Model Zero is found to compare well with Goldreich's solution (1968). It is concluded that the moon must have become freely yielding to tidal deformation at distances less than about 8 earth radii. Arguments are given in favor of the capture theory as a basis for the genesis of the moon.

Opik, E. J.↗
NASA NTRS1981

Origin of bright ring-shaped craters in radar images of Venus

Radar images of the Venusian surface taken at the Arecibo Observatory are examined in the context of recent study of the radar appearance of lunar craters to provide insight into the formation and evolution of Venusian features and to propose the thesis that bright ring-shaped features contain information about the rate at which Venus is being modified by depositional or erosional processes. Radar crater signatures are analyzed by crater floor and interior properties and by properties of ejecta deposits. Morphological comparisons with radar images of lunar craters are made, as well as morphometric comparisons with lunar radar crater haloes. The populations of radar bright craters on the moon and Venus is analyzed using a Monte Carlo simulation. It is concluded that the bright ring crater population does not resemble an impact crater production population.

Cutts, J. A.↗
NASA NTRS1962

LABORATORY. VOLUME I, NUMBERS 12-13

Discussion and photographs of ring structures surrounding lunar basins. evaluation and plates of russian photographs of the moon.

LUNAR PHOTOGRAPHY↗
NASA NTRS2002

Groundbased Radar Investigations of Asteroids and Planetary Satellites

Radar is a powerful source of information about the physical and dynamical properties of solar system bodies. Radar-detected targets include the Moon, Mercury, Mars, Venus, Phobos, Io, Europa, Ganymede, Callisto, Titan, Iapetus, Saturn's rings, eight comets, and 179 asteroids (75 main-belt and 104 near-Earth). This talk offers a perspective on the disc-integrated radar properties of solar system bodies and then turns to what radar remote sensing can tell us about asteroids using spatially-resolved measurements.

Ostro, S. J.↗
NASA NTRS1987

Collisional and dynamical processes in moon and planet formation

Research on a variety of dynamical processes relevant to the formation of planets, satellites and ring systems is discussed. The main focus is on studies of accretionary formation of early protoplanets using a numerical model, structures and evolution of ring systems and individual bodies within planetary rings, and theories of lunar origin.

Chapman, C. R.↗
NASA NTRS1986

The Voyager 2 encounter with the Uranian system

Discoveries which have occurred due to the success of the Voyager 2 flyby of Uranus and its moons are summarized, along with techniques used to maximize the data collected and minimize the demands on the spacecraft. The 11 spacecraft science packages, including photopolarimeters, spectrometers, a magnetometer, radios and a charged particle detector gathered information on the ring system, the scattering, emitting and reflecting characteristics of the Uranian atmosphere, and the five major satellites. The data revealed 10 minor satellites between Miranda and Uranus and the similarities between the Uranus, Saturn and Jupiter atmospheres. Extensive tabular data are provided for the physical dimensions of the nine rings and the 15 satellites. Finally, data on the magnetosphere and upper atmosphere environment of Uranus and imagery of the major moons are discussed.

Stone, E. C.↗
NASA NTRS1974

Mare Serenitatis - A preliminary definition of surface units by remote observations

Mare Serenitatis is a ringed mare about 600 km in diameter situated in the northeast quadrant of the moon. The floor of the mare is comprised of several units. Remote observations of Mare Serenitatis are presented. Color difference photographs were produced by photographing the moon at two wavelength bands. Radar images were obtained by delay-Doppler mapping of radar echoes. The definition of surface units is discussed together with surface properties obtained from remote observations.

Thompson, T. W.↗