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At least 613 records · Page 34

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NASA NTRS1977

Evaluation of Jupiter longitudes in System III/1965/

Commission 40 of the International Astronomical Union has adopted a new longitude system for Jupiter, labelled System III(1965), to replace the provisional System III(1957.0). The specification of the prime meridian and epoch for the new system differs slightly from that recently published. Its rotation rate implies a period of 9 hr 55 min 29.711 (plus or minus 0.04) sec, consistent with recent determinations from decimetric and decametric data. For both the new and older systems, equations are provided which are useful in the evaluation of longitudes for the analysis of Jupiter radio, particle, and field data from earth and spacecraft observations.

Seidelmann, P. K.↗

NASA NTRS1976

Jupiter's distant environment

Qualitative features of the distant Jovian magnetosphere which have been noted previously are reviewed. These features include the highly deformable or spongy nature of the outer regions, the temporal variability of the middle magnetosphere, the presence of a near-equatorial ring current sheet from about 30 Jupiter radii to the magnetopause and the regular oscillation of particle and field properties associated with planetary rotation. We next add evidence for the persistent presence of a layer of magnetic turbulence in the portion of the magnetosphere just inside the magnetopause and we examine its properties. The importance of the presence of the turbulent layer to theoretical models of the magnetosphere is stressed.

Kivelson, M. G.↗

NASA NTRS1977

A distance limit for a class of model gamma-ray burst sources

Gamma ray burst sources are presumably not larger than 10 to the 9th power cm as inferred from observed flux variations. If they are homogeneous and isotropically radiating, then from photon density considerations, they would have to be optically thick due to gamma-gamma pair production when assumed to be too far away. Deviations of observed photo spectra from an exponential shape around 1 MeV lead to an upper limit of the possible distance of such sources of only 2 kpc from the sun. Thus the sources must be galactic unless the radiation is highly beamed or emerges from a relativistically moving shell. This conclusion depends only on observed parameters. The possible presence of particles and fields in the sources would require them to be even closer.

Schmidt, W. K. H.↗

NASA NTRS1977

The role of plasma in the primeval nebula

The role of plasma and hydromagnetic processes in the primeval solar nebula is evaluated. In the light of the present knowledge of particles and fields in space it is difficult to avoid the conclusion that they must have played a crucial role in the emplacement of the material as well as its subsequent condensation into 'planetesimals'. Strong evidence in support of these processes in the primeval nebula is provided by the dynamical fine structure of the asteroidal belt and the Saturnian rings. The importance of current planetary magnetospheric as well as cometary research in clarifying certain physical processes believed to have occurred in the primeval nebula is stressed.

Alfven, H.↗

NASA NTRS1978

New concepts for Mercury orbiter missions

The next logical step in the exploration of Mercury is an orbiter mission. A conflict exists between those in the field of planetary sciences who desire a mission with a low circular orbit, and scientists in the fields and particles disciplines, who generally prefer a highly elliptical spacecraft orbit. The thermal environment imposed by the sun and planet render the low orbit intolerable for spacecraft using previous thermal control methods. A thermal control concept and a spacecraft mission concept have been developed which resolve these problems and promise a scientifically significant mission for the mid-1980s.

French, J. R.↗

NASA NTRS1978

Origin and evolution of the radio emission from immediate postoutburst supernovae

Several models for the radio emission from immediate postoutburst supernovae are examined under the assumption that the expanding remnant consists of a homogeneously mixed distribution of relativistic particles, magnetic field, and thermal plasma. The evolutionary models are: (1) an adiabatic expansion model; (2) a model incorporating the existence of a central pulsar; and (3) variations on the first two models in which relativistic electrons are accelerated either instantaneously or over an extended period of time and in which ionization, bremsstrahlung, synchrotron, Compton, and expansion losses are explicitly included. The character of the radio emission expected from these models is quite dissimilar. Whereas in adiabatic expansion models the emission is expected to increase slowly and become most intense at high frequencies, in models involving a central pulsar the emission should increase rapidly with a maximum flux density that is the same at all frequencies. The theoretical evolution of the radio emission for each model is compared with observations of SN 1970g.

Marscher, A. P.↗

NASA NTRS1975

Lunar Science Conference, 6th, Houston, Tex., March 17-21, 1975, Proceedings. Volume 3 - Physical studies

Recent investigations of the moon are reported. Topics discussed include the Apollo 17 site, selenography, craters, remote sensing, selenophysics, lunar surface fields and particles, magnetic properties of lunar samples, physical property measurements, surface-correlated properties, micrometeoroids, solar-system regoliths, and cosmic rays. Lunar orbital data maps are presented, and the evolution of lunar features is examined.

Merrill, R. B.↗

NASA NTRS1978

On the configuration of the magnetotail near midnight during quiet and weakly disturbed periods - State of the magnetosphere

Particle and field data are analyzed for a number of magnetically quiet days. It is shown that the magnetotail near midnight may exist for hours at a time in widely different quasi-stable configurations which, in their limit, can be characterized as being (1) fairly dipolelike to about 15 R(E), beyond which the field becomes taillike; and (2) dipolelike to only about 10 R(E), beyond which the field becomes taillike. These different states affect both the dynamics of the substorm and the evolution of the pitch angle distributions of energetic electrons in the near-earth plasma sheet past midnight. During quiet times, the plasma sheet in its azimuthal variation is at its thinnest in the region near midnight.

West, H. I., Jr.↗

NASA NTRS1978

The solar terrestrial observatory

The larger system of the earth environment is controlled externally by electromagnetic and particle energy from the sun. Recent studies have shown that the sun is a variable star with changes in its radiation which produce significant effects in the earth's climate and weather. The study of the solar-terrestrial system requires simultaneous, long-duration observations of the different elements or 'links' in the solar-terrestrial chain. Many investigations must be conducted in space from a vantage point above the earth's atmosphere where all of the sun's emissions can be observed free from atmospheric distortion, where the magnetospheric particles and fields can be measured directly, and where the atmosphere can be observed on a global scale. The extension of the Shuttle on-orbit capability in connection with the development of the power module will offer an important near-term step in an evolutionary process leading toward a permanent manned Solar Terrestrial Observatory capability in low-earth orbit. Attention is given to the required solar-terrestrial measurements, the operation of the Solar Terrestrial Observatory, and an evolutionary approach to the Solar Terrestrial Observatory.

Chappell, C. R.↗

NASA NTRS1978

High beta plasma in the dynamic Jovian current sheet

The equatorial current sheet, which Pioneer 10 repeatedly encountered on its outbound pass through the Jovian magnetosphere, frequently was associated with intense fluxes of energetic protons. Simultaneous observations of the changes in the energetic proton flux and in the magnetic-field magnitude demonstrate that the current sheet is embedded in a high-beta plasma in which high-energy (above 60 keV) ions frequently are the dominant constituents. Large differences in the plasma temperature and the thickness of this plasma sheet between encounters only 10 hours apart indicate that the Jovian plasma sheet is very dynamic on a time scale of hours. Occasional observations of significant temporal variations in the magnetic field and particle populations during periods within the plasma sheet may represent in situ observations of Jovian magnetic disturbances. Comparison with previous observations suggests that low-energy (not more than 5 keV) plasma contributes less than 3% to the current-sheet energy density.

Walker, R. J.↗

NASA NTRS1978

Report on active and planned spacecraft and experiments

Information is presented, concerning active and planned spacecraft and experiments known to the National Space Science Data Center. The information included a wide range of disciplines: astronomy, earth sciences, meteorology, planetary sciences, aeronomy, particles and fields, solar physics, life sciences, and material sciences. These spacecraft projects represented the efforts and funding of individual countries as well as cooperative arrangements among different countries.

Vette, J. I.↗

NASA NTRS1979

Report on Active and Planned Spacecraft and Experiments

Information concerning concerning active and planned spacecraft and experiments known to the National Space Science Data Center are included. The information contains a wide range of disciplines: astronomy, earth sciences, meteorology, planetary sciences, aeronomy, particles and fields, solar physics, life sciences, and material sciences. These spacecraft projects represent the efforts and funding of individual countries as well as cooperative arrangements among different countries. Approximately 850 articles are included.

Vostreys, R. W.↗

NASA NTRS1978

The Pioneer Venus spacecraft program

The Pioneer Venus program consists of two spacecraft: an orbiter and a multiprobe. Both will arrive at Venus in early December 1978. The orbiter will collect data on the upper atmosphere and fields and particles and will sense the clouds and surface remotely from a 75 deg inclined orbit. The multiprobe consists of a bus, three small probes, and a large probe. All five objects will enter the Venus atmosphere and will transmit data on its characteristics directly to earth while descending to the surface. The development of these spacecraft required the solution of many difficult and unique technical problems.

Dorfman, S. D.↗

NASA NTRS1979

The interaction of the solar wind with Mars, Venus and Mercury

The history of investigation of the solar wind interaction with Mars, Venus, and Mercury is reviewed, and our knowledge on this interaction for each of the three planets is compared. The primary objective is to gain insight into the basic physical mechanisms operative in the earth's magnetosphere from a study of (the somewhat different) magnetospheres of the planets under consideration. Mercury and Venus have significant dipole moments which play an important part in solar wind interaction. The Martian magnetic moment appears to be too weak to influence solar wind interaction. As expected, the bow shock of Mercury and the earth are quite similar since the magnetic moment of each is sufficient to stand off the solar wind. The shocks of Venus and Mars are also similar, but the Venusian shock lies much closer to the planet than the Martian shock. Both Mercury and Venus show evidence of substorm-like field and particle behavior, but with clear differences in the time scale.

Russell, C. T.↗

NASA NTRS1980

Report on active and planned spacecraft and experiments

Information on current and planned spacecraft activity for a broad range of scientific disciplines is presented. The information covers a wide range of disciplines: astronomy, Earth sciences, meteorology, planetary sciences, aeronomy, particles and fields, solar physics, life sciences, and material sciences. These spacecraft projects represent the efforts and funding of individual countries as well as cooperative arrangements among different countries.

Horowitz, R.↗

NASA NTRS1979

Correlation of lunar far-side magnetized regions with ringed impact basins

By the method of electron reflection, we have identified seven well-defined magnetized regions in the equatorial belt of the lunar far side sampled by the Apollo 16 Particles and Fields subsatellite. Most of these surface magnetic fields lie within one basin radius from the rim of a ringed impact basin, where thick deposits of basin ejecta are observed or inferred. The strongest of the seven magnetic features is linear, at least 250 km long, and radial to the Freundlich-Sharonov basin. The apparent correlation with basin ejecta suggests some form of impact origin for the observed permanently magnetized regions.

Anderson, K. A.↗

NASA NTRS1980

A macroscopic profile of the typical quasi-perpendicular bow shock - Isee 1 and 2

A macroscopic examination of field and particle properties of the bow shock recorded on November 5, 1977, identified earlier as stable features by comparison of Isee 1 and 2 data, is presented. Attention is given to the extent to which the shock was in a typical state, and multidiagnostic observations are combined to define the shock profile. It is found that the shock profile offered several unanticipated structural features, which include a variable directional profile of the reflected proton group passing through the front, an electrostatic boundary effect associated with the reflected protons upstream, and an oscillatory buildup of proton thermalization behind the overshoot portion of the shock signature.

Greenstadt, E. W.↗

NASA NTRS1981

Sounding rocket research Aries/Firewheel, series 22, issue 15

Rocket experiments in ionospheric particle and field research flow in seven programs during the last decade are summarized. Experimental techniques were developed and are discussed including the double-probe field technique. The auroral zone, polar cap, and equatorial spread F were studied.

Mozer, F. S.↗