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NASA NTRS1975

Planets and satellites of the outer solar system, asteroids, and comets

The cosmogenic significance of outer solar system objects is evaluated with emphasis on planets and larger satellites of greatest biological interest; comets, asteroids, and the smaller satellites are also discussed. Principal physical and rudimentary photometric data for the five outer planets are presented in tables. Sufficient information on planetary motions is included for most calculations in physical planetology.

Newburn, R. L., Jr.↗

NASA NTRS1975

Electrostatic noise bands associated with the electron gyrofrequency and plasma frequency in the outer magnetosphere

Naturally occurring noise bands near the electron plasma frequency are frequently detected by the University of Iowa plasma wave experiment on the Imp 6 satellite in the region from just inside the plasmapause to radial distances of about 10 earth radii in the outer magnetosphere. The electric field strength of these noise bands is usually small with typical broad band electric field strengths of about 2 microvolts per m. A magnetic field has been detected only in a few unusually intense cases, and in these cases the magnetic field energy density is several orders of magnitude smaller than the electric field energy density. The bands are observed at all magnetic latitudes covered by the Imp 6 orbit and appear to be a permanent feature of the outer magnetosphere. They are found at all local times and occur least frequently in the quadrant from 18 to 24 hours. The bands appear to consist of two distinct spectral types called diffuse and narrow band. In both types the center frequency of the noise band is bounded by consecutive harmonics of the electron gyrofrequency, and these noise bands occur most often between harmonics that are near the local electron plasma frequency.

Shaw, R. R.↗

NASA NTRS1976

Expansion of an X-ray coronal arch into the outer corona

An asymmetric expanding arch photographed in the inner corona with an X-ray telescope on August 13, 1973, is identified as the source of the mass ejected in a white-light transient in the outer corona. The morphology, angular position, estimated mass, and apparent rate of upward acceleration of the lower coronal arch are similar to those of the arch seen passing through the outer corona. The mass of material removed from the lower corona is estimated to be 2 by 10 to the 15th power g, and the upward motion is consistent with a constant acceleration of 12.5 m/sec per sec between 1.3 and 5 solar radii.

Rust, D. M.↗

NASA NTRS1976

Performance of 75-millimeter bore arched outer-race ball bearings

An investigation was performed to determine the operating characteristics of 75-mm bore, arched outer-race bearings, and to compare the data with those for a similar, but conventional, deep groove ball bearing. Further, results of an analytical study, made using a computer program developed previously, were compared with the experimental data. Bearings were tested up to 28,000 rpm shaft speed with a load of 2,200 N (500 lb). The amount of arching was 0.13, 0.25, and 0.51 mm (0.005, 0.010, and 0.020 in). All bearings operated satisfactorily. The outer-race temperatures and the torques, however, were consistently higher for the arched bearings than for the conventional bearings

Coe, H. H.↗

NASA NTRS1977

Plasma electron measurements in the outer Jovian magnetosphere

The existence of the plasma electrons in the outer Jovian magnetosphere reported by Intriligator and Wolfe (1974) is consistent with (1) the additional pressure needed to supplement the magnetospheric magnetic field in the outer magnetosphere so as to balance the solar wind and interplanetary magnetic field dynamic pressure across the magnetopause, (2) the drastic change in the plasma electron spectrum as soon as Pioneer 10 crossed the magnetopause from the magnetosheath into the magnetosphere, (3) the fact that the instrument aperture was at spacecraft ground, and (4) the fact that beyond about 2 AU the continuous observations of all ambient electron fluxes (solar wind electrons, secondary electrons, photoelectrons, etc.) are below the instrument threshold.

Intriligator, D. S.↗

NASA NTRS1977

Identification of a new class of satellites in the outer solar system

From near-infrared photometry (JHKL) of small bodies in the outer solar system a previously unrecognized class of planetary satellites is identified which may have surfaces mostly free of frosts of water, methane, or ammonia. These bodies - including two satellites of Uranus (Titania and Oberon), and one each of Saturn (Hyperion) and Neptune (Triton) - have surfaces characterized by neutral reflectance between J and H (1.25 and 1.60 microns) and rapidly decreasing reflectance at K (2.2 microns) and L (3.5 microns). It is pointed out that the 15 solid bodies in the outer solar system that have been satisfactorily observed (excluding the asteroids) fall into six classes according to spectral reflectance. The presence of water frost or ice on the surface of Enceladus is established.

Cruikshank, D. P.↗

NASA NTRS1978

Acceleration of protons at 32 Jovian radii in the outer magnetosphere of Jupiter

A rapid ten-fold increase of proton flux was observed at 32 Jovian radii in Jupiter's outer magnetosphere. The total event lasted about 30 minutes and was composed of many individual events. Both before and after the event, proton flux was similar to the low-flux level found between crossings of the magnetic equator. Measurements of angular distributions and the time histories of proton and alpha particle channels at different energies indicate that the flux increase is caused by local acceleration. It is suggested that the average particle population in the outer magnetosphere is caused by a state of dynamic equilibrium between acceleration and loss processes.

Schardt, A. W.↗

NASA NTRS1978

Equation of state fits to the lower mantle and outer core

The lower mantle and outer core are subjected to tests for homogeneity and adiabaticity. An earth model is used which is based on the inversion of body waves and Q-corrected normal-mode data. Homogeneous regions are found at radii between 5125 and 4825 km, 4600 and 3850 km, and 3200 and 2200 km. The lower mantle and outer core are inhomogeneous on the whole and are only homogeneous in the above local regions. Finite-strain and atomistic equations of state are fit to the homogeneous regions. The apparent convergence of the finite-strain relations is examined to judge their applicability to a given region. In some cases the observed pressure derivatives of the elastic moduli are used as additional constraints. The effect of minor deviations from adiabaticity on the extrapolations is also considered. An ensemble of zero-pressure values of the density and seismic velocities are found for these regions. The range of extrapolated values from these several approaches provides a measure of uncertainties involved.

Butler, R.↗

NASA NTRS1979

On the internal structure of the major satellites of the outer planets

The structures and thermal evolutions of the large icy-satellites of the outer solar system are considered. It is shown (for bodies comparable in size and mass to the Galilean satellites, having sizeable mass fraction of H2O, and with meteoritic abundances of radioactive materials contained within their silicate fractions) that the crust of solid ice over a liquid mantle predicted by conductive heat-transfer calculations is unstable to large-scale solid-state convection. For appropriate material parameters, convective heat-transfer rates are sufficient to freeze a large liquid mantle on a time scale that is short compared to the lifetime of the body. It is also concluded that the ice layer is convecting at the present time. A reevaluation of previous work, using improved values for material parameters and boundary conditions, reverses earlier conclusions and implies a rigid outer crust with resulting long-term stability of surface features to creep deformation. The combination of a rigid crust with active internal convection presents the additional possibility of surface features that are produced and maintained by dynamic internal processes.

Reynolds, R. T.↗

NASA NTRS1979

Fields and plasmas in the outer solar system

The most significant data on fields and plasmas in the outer solar system, based on observations by Pioneer 10 and 11, are reviewed. Attention is given to (1) corotating shocks and the evolution of high speed solar wind streams, (2) the effect of the changing structure of the interplanetary medium on energetic particles, (3) the propagation of flare-generated shocks through the outer solar system, (4) radial gradients in the solar wind and interplanetary field, and (5) the dependence of the interplanetary sector structure on heliographic latitude.

Smith, E. J.↗

NASA NTRS1979

Solar electric earth gravity assist /SEEGA/ missions to the outer planets

The optimization of solar electric propulsion earth-gravity-assist trajectories to the outer planets is presented. Included in the optimization is both earth swingby velocity and swingby date. Mission modes with and without optimal post swingby thrust are compared. Performance suitable for preliminary mission studies is presented for the four major outer planets using circular-coplanar planetary orbits and additional performance is presented for a Saturn Orbiter-Dual Probe mission.

Sauer, C. G.↗

NASA NTRS1980

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time varying magnetic field and their pitch-angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, through elementary exercises, is used to predict the consequences of the process for cases that are not tractable by analytical means. For energy dependent pitch angle diffusion rates, characteristic 'two temperature' distributions are produced. Application of the model to the outer Jovian magnetosphere shows that beyond 20 Jupiter radii in the outer magnetosphere, particles may be magnetically pumped to energies of the order of 1 - 2 MeV. Two temperature distribution functions with "break points" at 1 - 4 KeV for electrons and 8 - 35 KeV for ions are predicted.

Borovsky, J. E.↗

NASA NTRS1979

Distant asteroids and outer Jovian satellites

Sixty percent of the sampled objects in the Hilda, Trojan and outer Jovian satellite locations belong to C-type and another 30% belong to a new group called RD-type (reddish and dark), sometimes referred to simply as D-type. Objects in this group have low albedo values between 2 and 4% and steep reflection spectra between 0.7 micron and 0.9 micron. Furthermore, 944 Hidalgo belongs to this group but shows color variation over its surface. Meteoritic minerals with similar optical reflection spectra are discussed. Trojans with sizes down to 15 km in the cloud preceding Jupiter are about 3.5 times more numerous than those in the following cloud. RD-type Trojans appear more often in the preceding cloud. There is a resemblance of spectrum, albedo and phase relation among the majority of Trojans and the outer Jovian satellites.

Degewij, J.↗

NASA NTRS1981

Stability of outer planetary systems

The conditions for stability in the Liapunov-Hill sense of outer planetary systems are given in terms of radii of planetary orbits. The outer planets of the solar system are found stable and the possible existence of other than the presently known planets between Jupiter and Pluto are indicated. The existence of other planetary systems with arbitrary mass ratios of the primaries is suggested, and the stability conditions for such systems are derived.

Szebehely, V.↗

NASA NTRS1981

An acceleration mechanism for loop transients in the outer corona

The heliocentrifugal motion of coronal loop transients is likely driven largely by the buoyant force exerted by the ambient medium. In the outer corona where the solar wind is well formed, the buoyant force results mainly from the rapid outward decrease in the ambient pressure of the solar wind. The contribution from magnetic buoyancy is not so significant as in the vicinity of the solar surface. Therefore, the pertinent features of the loop transients in the outer corona are basically gasdynamical. As a conspicuous part of coronal expansion, the motion of the compressible masses in the transient loops is largely controlled by thermal forces. The translational motion of heliocentrifugal expansion is driven by the hydrodynamic buoyant force, and the lateral motion of peripheral expansion is driven by the pressure difference between the dense plasma of the ejecta and the tenuous plasma of the ambient medium.

Yen, T.↗

NASA NTRS1981

Magnetic pumping of particles in the outer Jovian magnetosphere

The mechanism of magnetic pumping consists of two processes, the adiabatic motion of charged particles in a time-varying magnetic field and their pitch angle diffusion. The result is a systematic increase in the energy of charged particles trapped in mirror (and particularly, magnetospheric) magnetic fields. A numerical model of the mechanism is constructed, compared with analytic theory where possible, and, is used to predict the consequences of the process for cases that are not tractable by analytical means. The model is applied to the outer Jovian magnetosphere for two purposes; to find magnetospheric regions in which the mechanism may energize trapped particles, and to generate distribution functions involving pitch angle diffusion caused by wave-particle interactions. Beyond 20 Jupiter radii in the outer magnetosphere particles may be magnetically pumped to energies of the order of 1-2 MeV and two-temperature distribution functions with 'break points' at 1-4 keV for electrons and 8-35 keV for ions are predicted.

Borovsky, J. E.↗

NASA NTRS1981

Dynamics of the outer radiation belts in relation to polar substorms and hot plasma injections at geostationary altitude

Geostationary satellite and ground measurements of dynamic variations of the outer radiation belts and their relations with the development of auroral structures during magnetospheric substorms are analyzed. A comparison of measurements of the H or X geomagnetic field components made by seven auroral stations with ATS-6 low-energy and high-energy particle measurements during the multiple-onset substorm of Aug. 16, 1974 is presented which demonstrates that while the decrease in energetic particle fluxed ends only at the time of a strong substorm onset, rapid motions of the outer radiation belts may occur during the flux decrease. All-sky photographs of auroral phenomena taken at Fort Yukon and College, Alaska are then compared with ATS-1 energetic particle flux measurements in order to demonstrate the relation between flux decreases and increases and distinct substorm phases. Results support the hypothesis of a magnetospheric substorm precursor which appears to be an instability growing at the inner boundary of the plasma layer and approaching the earth, and underline the importance of current and magnetic field variations in charged particle dynamics.

Sauvaud, J. A.↗

NASA NTRS1981

Derivation of the collision probability between orbiting objects The lifetimes of Jupiter's outer moons

A general form is derived for Opik's equations relating to the probability of collision between two orbiting objects to their orbital elements, and used to determine the collisional lifetime of the eight outer moons of Jupiter. The derivation is based on a concept of spatial density, or average number of objects found in a unit volume, and results in a set of equations that are easily applied to a variety of orbital collision problems. When applied to the outer satellites, which are all in irregular orbits, the equations predict a relatively long collisional lifetime for the four retrograde moons (about 270 billon years on the average) and a shorter time for the four posigrade moons (0.9 billion years). This short time is suggestive of a past collision history, and may account for the orbiting dust detected by Pioneers 10 and 11.

Kessler, D. J.↗