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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 109 records · Page 6
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DOE OSTI2020

Retention of Long-period Gas Giant Planets: Type II Migration Revisited

During their formation, emerging protoplanets tidally interact with their natal disks. Proto–gas giant planets, with Hill radii larger than the disk thickness, open gaps and quench gas flow in the vicinity of their orbits. It is usually assumed that their type II migration is coupled to the viscous evolution of the disk. Although this hypothesis provides an explanation for the origin of close-in planets, it also encounters a predicament on the retention of long-period orbits for most gas giant planets. Moreover, numerical simulations indicate that the planets' migrations are not solely determined by the viscous diffusion of their natal disk. In this work, we carry out a series of hydrodynamic simulations combined with analytic studies to examine the transition between different paradigms of type II migration. We find a range of planetary mass for which gas continues to flow through a severely depleted gap so that the surface density distribution in the disk region beyond the gap is maintained in a quasi-steady state. The associated gap profile modifies the location of corotation and Lindblad resonances. In the proximity of the planet's orbit, high-order Lindblad and corotation torque are weakened by the gas depletion in the gap, while low-order Lindblad torques near the gap walls preserve their magnitude. Consequently, the intrinsic surface density distribution of the disk delicately determines both the pace and direction of the planets' type II migration. We show that this effect might stall the inward migration of giant planets and preserve them in disk regions where the surface density is steep.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Life beyond the solar system.

Review of some of the highlights and more recent developments in the search for extraterrestrial intelligence. The first major problem is one of the generality of the formation of planetary systems. Observations of the nearest stars which are not members of binary or multiple stars indicates that fully half have companions of planetary mass. The presence of organic compounds in meteorites, probably in Jovian planets, in comets, in the interstellar medium, and in cool stars implies that the production of organic compounds essential for the origin of life should be pervasive throughout the universe. Possibilities of interstellar communication are discussed.

Sagan, C.↗
NASA NTRS1971

Our present state of ignorance of the outer planets and their satellites.

Although the outer solar system contains the bulk of the angular momentum of the system and a huge fraction of the total planetary mass, very little is actually known about it. Massive Jupiter, with its low mean density and huge red spot (possibly a Taylor column), shows a complex rotational pattern as a result of three rotating systems, each having a different period. Atmospheric scattering of the reflected solar radiation makes spectral interpretation uncertain. Imprecisions in the Bond albedo cause discrepancies between actual and predicted solar energy absorbed. Saturn is similar to Jupiter in massiveness, low density, atmospheric aerosols, and albedo. Its rings are believed to be largely water ice. To date, no evidence of radiation belts, analogous to Jupiter's, exists for Saturn, Uranus, or Neptune. Methane and hydrogen have been detected in the atmospheres of all these planets, but the mole fraction of hydrogen is lower in the atmospheres of Uranus and Neptune. Uranus' 98 degree inclination will provide basis for study of its atmospheric circulation. Our knowledge of Pluto is restricted to the sparsest physical data.

Rea, D. G.↗
NASA NTRS1975

Jupiter: As a planet

The planet Jupiter, its planetary mass and atmosphere, radio waves emitted from Jupiter, thermal radiation, internal structure of Jupiter, and the possibility of life on Jupiter are discussed. Educational study projects are included.

Source record↗
NASA NTRS1975

Asteroid collisional evolution - Evidence for a much larger early population

The present population of asteroids is a remnant of a vastly larger one that contained perhaps a planetary mass, dominantly distributed in planetesimals approximately 500 kilometers or less in diameter. It constituted a large reservoir of objects that plausibly were responsible for cratering the moon, Mars, and Mercury. Much asteroidal dust may have accumulated on Mars and other planets.

Chapman, C. R.↗
NASA NTRS1977

Geologic evolution of the terrestrial planets

The paper presents a geologic comparison of the terrestrial planets Mercury, Venus, Earth, the Moon and Mars, in the light of the recent photogeologic and other evidence gathered by satellites, and discusses the relationships between their regional terrain types, ages, and planetary evolution. The importance of the two fundamental processes, impact cratering and volcanism, which had formed these planets are stressed and the factors making the earth unique, such as high planetary evolution index (PEI), dynamic geological agents and the plate tectonics, are pointed out. The igneous processes which dominate earth and once existed on the others are outlined together with the planetary elevations of the earth which has a bimodal distribution, the moon which has a unimodal Gaussian distribution and Mars with a distribution intermediate between the earth and moon. Questions are raised concerning the existence of a minimum planetary mass below which mantle convection will not cause lithospheric rifting, and as to whether each planet follows a separate path of evolution depending on its physical properties and position within the solar system.

Head, J. W.↗
NASA NTRS1977

Expressions for the precession quantities based upon the IAU /1976/ system of astronomical constants

The structure of the expressions usually employed in calculating the effects of precession is examined, and a method is outlined for revising the expressions to account for changes in the fundamental astronomical constants. It is shown that the basic set of parameters, upon which depend the lengthy polynomials for computing the mean obliquity of data and the elements of the precession matrix, consists of the mean obliquity, the speed of general precession in longitude at a fixed epoch, and the system of planetary masses. Special attention is given to the motion of the ecliptic pole, formulations for a basic epoch as well as an arbitrary epoch, and ecliptic motion relative to the basic epoch. Numerical precession quantities at epoch J2000.0 (JED 2451545.0) are presented which result from the revision of astronomical constants adopted at the XVI General Assembly of the IAU.

Lieske, J. H.↗
NASA NTRS1977

Properties of satellite orbits - Ephemerides, dynamical constants, and satellite phenomena

A short account is given of the history of the observation of the Galilean satellites, with an emphasis on early orbital work and practical applications thereof to world mapping and navigation. The general character of satellite motion is described from a geometric and physical point of view without reference to mathematics. This is followed by a similar discussion of ordinary and mutual satellite phenomena. The accuracies of published ephemerides are discussed on the basis of the observations and theories available for the various satellites. The ephemeris tables need to be revised and, perhaps, partly replaced by well-documented computer programs. The determination of physical parameters (planetary masses and oblatenesses; masses, sizes, and albedo maps of satellites) from positional observations of satellites and photometric observations of ordinary and mutual satellite phenomena is discussed.

Aksnes, K.↗
NASA NTRS1980

In search of other planetary systems

Numerous recent developments have led to an increasing awareness of and interest in the detection of other planetary systems. A brief review of the modern history of this subject is presented with emphasis on the status of data concerning Barnard's star. A discussion is given of plausible observable effects of other planetary systems with numerical examples to indicate the nature of the detection problem. Possible types of information (in addition to discovery) that observations of these effects might yield (e.g., planetary mass and temperature) are outlined. Also discussed are various candidate detection techniques (e.g., astrometric observations) which might be employed to conduct a search, the current state-of-the art of these techniques in terms of measurement accuracy, and the capability of existing or planned facilities (e.g., space telescope) to perform a search. Finally, consideration is given to possible search strategies and the scope of a comprehensive search program.

Black, D. C.↗
NASA NTRS1985

Volatile loss following very large impacts

Large impacts on growing planets can be fundamentally different in outcome than small impacts because they can lead to a planet-enveloping cloud of siliate vapor with a radiative cooling time long compared to dynamic time scales. Under these circumstances, there can be preferrential volatile loss by hydrodynamic outflow immediately above the silicate cloud deck. This loss is in ddition to the prompt, nonpreferential loss immediately following the impact event. During this time, evaporative loss (Jeans loss) can be 0.00001 of the planetary mass, provided the impact has substantial angular momentum and a magma disk forms. The loss is preferentially fromt he extremities of the disk and can be easily s100 bar-equivalents of CO2 or H2O. This implies devolatilization of Moon-forming material in an impact origin and may have important implications for the CO2 reservoirs of Venus, Earth, and Mars.

Stevenson, D. J.↗
NASA NTRS1985

Review of methodology and technology available for the detection of extrasolar planetary systems

Four approaches exist for the detection of extrasolar planets. According to the only direct method, the planet is imaged at some wavelength in a manner which makes it possible to differentiate its own feeble luminosity (internal energy source plus reflected starlight) from that of the nearby host star. The three indirect methods involve the detection of a planetary mass companion on the basis of the observable effects it has on the host star. A search is conducted regarding the occurrence of regular, periodic changes in the stellar spatial motion (astrometric method) or the velocity of stellar emission line spectra (spectroscopic method) or in the apparent total stellar luminosity (photometric method). Details regarding the approaches employed for implementing the considered methods are discussed.

Tarter, J. C.↗
NASA NTRS1987

Accumulation of solid bodies in the solar nebula

Research on the accumulation of solid bodies in the solar nebula is discussed. Studies of the earliest stage of accumulation of solid bodies in the solar system, which occured in the presence of the gaseous component of the solar nebula, are discussed. The combined effects of gas drag and gravitational perturbations of a planetary embryo on the orbital evolution of planetesimals, the effects of resonant trapping on planetesimals, and planetary mass accretion are discussed.

Weidenschilling, S. J.↗
NASA NTRS1986

Evolution of super-Jupiters

The physics of the interiors of Jovian-class objects is reviewed, and its extension to substellar objects is discussed. Some results are presented for objects cooling from effective temperatures starting at 2500 K. The interior calculations are coupled to model atmosphere surface conditions computed by Lunine; the latter are continued to higher temperatures and pressures in the ideal gas region and are then matched by entropy to the strongly-coupled interior region. Except in the planetary-mass models, this transition region occupies a negligible fraction of the total mass. For the observed parameters of VB8B, only models with masses in excess of 0.05 solar mass have cooling ages above a billion years. Thus, for plausible VB8B lifetimes, this object is likely to be close to the critical hydrogen-ignition mass.

Hubbard, W. B.↗
NASA NTRS1987

On the apparent velocity of integrated sunlight. I - 1983-1985

Frequency measurements for the Delta V = 2 transitions of CO in the integrated light spectrum of the sun are presented. The nature and magnitude of systematic errors which typically arise in absolute velocity measurements of integrated sunlight are explored in some detail, and measurements believed accurate at the level of about 5 m/s or less are presented. It is found that the integrated light velocity varies by about 3 m/s or less over a one-day period. Over the long term, the data indicate an increasing blue-shift in these weak infrared lines amounting to 30 m/s from 1983 to 1985. The sense of the drift is consistent with a lessening in the magnetic inhibition of granular convection at solar minimum. Such an effect has implications for the spectroscopic detectability of planetary-mass companions to solar-type stars.

Deming, Drake↗
NASA NTRS1988

Prediction of radio frequency power generation of Neptune's magnetosphere from generalized radiometric Bode's law

Magnetospheric radio frequency emission power has been shown to vary as a function of both solar wind and planetary values such as magnetic field by Kaiser and Desch (1984). Planetary magnetic fields have been shown to scale with planetary variables such as density and angular momentum by numerous researchers. This paper combines two magnetic scaling laws with the radiometric law to yield 'Bode's'-type laws governing planetary radio emissions. Further analysis allows the reduction of variables to planetary mass and orbital distance. These generalized laws are then used to predict the power otuput of Neptune to be about 1.6 x 10 to the 7th W; with the intensity peaking at about 3 MHz.

Million, M. A.↗
NASA NTRS1992

Cometary orbital evolution in the outer planetary region

Numerical integrations of fictitious objects are carried out in order to elucidate the dynamical behavior of potential short-period comets when they move in orbits at distances from the Sun comparable to those of Uranus and Neptune. As in the case of observed short-period comets, close encounters with the planets play a major role for the orbital evolution, and this is especially true for encounters with initial orbits nearly tangent to that of the planet. A comparison with integrations in which the planetary masses are larger by a factor 10 shows that, in the latter case, the orbital evolution is greatly accelerated, but the dynamical paths in phase space followed by the comets are altered.

Manara, Allesandro↗
NASA NTRS1993

Orbit determination error analysis and comparison of station-keeping costs for Lissajous and halo-type libration point orbits and sensitivity analysis using experimental design techniques

Spacecraft in orbit near libration point L1 in the Sun-Earth system are excellent platforms for research concerning solar effects on the terrestrial environment. One spacecraft mission launched in 1978 used an L1 orbit for nearly 4 years, and future L1 orbital missions are also being planned. Orbit determination and station-keeping are, however, required for these orbits. In particular, orbit determination error analysis may be used to compute the state uncertainty after a predetermined tracking period; the predicted state uncertainty levels then will impact the control costs computed in station-keeping simulations. Error sources, such as solar radiation pressure and planetary mass uncertainties, are also incorporated. For future missions, there may be some flexibility in the type and size of the spacecraft's nominal trajectory, but different orbits may produce varying error analysis and station-keeping results. The nominal path, for instance, can be (nearly) periodic or distinctly quasi-periodic. A periodic 'halo' orbit may be constructed to be significantly larger than a quasi-periodic 'Lissajous' path; both may meet mission requirements, but perhaps the required control costs for these orbits are probably different. Also for this spacecraft tracking and control simulation problem, experimental design methods can be used to determine the most significant uncertainties. That is, these methods can determine the error sources in the tracking and control problem that most impact the control cost (output); it also produces an equation that gives the approximate functional relationship between the error inputs and the output.

Gordon, Steven C.↗
NASA NTRS1994

On the detection of mutual perturbations as proof of planets around PSR1257+12

Unambiguous detection of the consequences of mutual perturbations of the hypothesized planets about the pulsar PSR1257+12 would be unassailable proof of their existence. Nearly all of the residuals in the times of arrival (TOA) of the pulses after subtraction of the TOA predicted from the best fit constant period model are accounted for by including the effects of two orbiting planets with constant orbital parameters. The nature and magnitude of additional residuals in the TOA due to the gravitational interactions between the planets are determined by numerically calculating the TOA residuals for the orbital motion including the perturbations and subtracting the TOA residuals from analytic expressions of the orbital motion with orbital parameters fixed at averaged values. The TOA residual differences so obtained oscillate with periods comparable to the orbital periods with the oscillations varying in amplitude as a function of epoch within any given observational period. The signature of the perturbations is thus a quasiperiodic modulation of the residual differences obtained after removal of the effects of the orbital motion with best fit, constant orbital parameters. The amplitudes of this modulation reach about 10 microsecond for observational periods exceeding 1000 days for the minimum planetary masses with sin i = 1, and they increase as 1/sin i for 1/sin i less than 5, where i is the inclination of the orbit plane to that of the sky. Greater accumulated phase differences between the effects of perturbed and unperturbed orbital motions are available in the times of zero values in the observed and predicted TOA residuals and these comprise a second signature of the perturbations. The perturbation signatures should become detectable as the observation interval approaches 1000 days.

Peale, S. J.↗