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  • LUNAR AND PLANETARY EXPLORATION  (164)
  • 1980-1984  (164)
  • 1970-1974
  • 1965-1969
  • 1935-1939
  • 1981  (164)
  • 11
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    Fermi-Compton scattering due to magnetopause surface fluctuations in Jupiter's magnetospheric cavity (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The effects of boundary surface fluctuations on a spectrum of electromagnetic radiation trapped in a high Q (quality) cavity are considered. Undulating walls introduce small frequency shifts at reflection to the radiation, and it is argued that the process is entirely analogous to both Fermi (particle) acceleration and inverse Compton scattering. A Fokker-Planck formalism is pursued; it yields a diffusion equation in frequency for which the Green's function and steady-state solutions are found. Applying this analysis to the Jovian continuum radiation discovered by Voyager spacecraft, it is suggested that characteristic diffusion times are greater than 1 year, and that in order to account for the steep frequency spectra observed, an unidentified loss mechanism must operate in the cavity with a decay time constant approximately equal to the characteristic diffusion time divided by 28. A radiator-reactor model of the cavity is investigated to provide an estimate for the intrinsic luminosity of the low frequency (approximately 100 Hz) continuum source whose power is approximately 7 x 10 to the 6th W.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Astrophysical Journal; vol. 243
    Format: text
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  • 12
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    Cosmic-ray-produced Cl-36 and Mn-53 in Allan Hills-77 meteorites (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Cosmic-ray-produced Mn-53 has been determined by neutron activation in nine Allan Hills-77 meteorites. Additionally, Cl-36 has been measured in seven of these objects using tandem accelerator mass spectrometry. These results, along with C-14 and Al-26 concentrations determined elsewhere, yield terrestrial ages ranging from 10,000 to 700,000 years. Weathering was not found to result in Mn-53 loss.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters; 52; 1, Ja; Jan. 198
    Format: text
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  • 13
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    Jupiter tail phenomena upstream from Saturn (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Plasma wave and plasma probe measurements from Voyager 2 for February 1981 suggest the detection of phenomena associated with a well defined Jupiter tail, at a distance of about 6,200 Jovian radii. This is held to imply that the Saturn magnetosphere will be affected by the Jovian tail, and that insight into the physics of Saturn's magnetosphere may be obtained through comparisons of Voyager 1 and 2 data. Among the effects that can be sought in Voyager 2 data are magnetosphere size variations, bow shock location, radio emission strength and trapped radiation belt population.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 292; Aug. 13
    Format: text
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  • 14
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    Local Mars dust storm generation mechanism (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: On an areocentric solar longitude of 340 deg, first Mars year of Viking on the surface, a local dust storm was observed at the Viking Lander No. 1 site by Viking Orbiter A. The storm lasted less than one Martian day (sol) with the dust raised affecting the site for about three sols. It is concluded that this storm was caused by baroclinic waves and that the threshold wind speed for saltation was 25-30 m/sec.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Geophysical Research Letters; 8; Aug. 198
    Format: text
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  • 15
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    Generation of Martian chaos and channels by debris flows (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A debris flow mechanism is proposed to account for the formation of chaos and the large channels debouching into Crysae Planitia from the adjacent southern uplands of Mars. Based on considerations of the juxtaposition of individual channel environments, the morphological assemblages within each environment and flow dynamics, it is suggested that the debris flows were triggered by the large-scale failure of subsurface sediments, possibly initiated by a seismic event. During the initial, slow-moving phase of the flow, the debris would have formed gently sinuous channels with multiple side-wall slumps, grooves and ridges, and elongate erosional remnants. The flow would have gained mobility as the debris moved downslope, producing travel distances greatly in excess of those characteristic of terrestrial examples, and eroded, streamlined remnants at the distal reaches of the channel. Finally, due to internal and boundary friction, the flow would have been slowed down once it entered the Chryse plains, resulting in a thin debris blanket with no depositional relief.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 45; Jan. 198
    Format: text
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  • 16
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    Plasma observations near Saturn - Initial results from Voyager 1 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Voyager 1 encounter with Saturn and its satellites yielded extensive measurements of magnetospheric low-energy plasma electrons and positive ions, both heavy and light, probably of hydrogen and nitrogen or oxygen. At radial distances between 15 and 7 Saturn radii on the inbound trajectory, the plasma appears to corotate with a velocity within 20% of that theoretically expected for rigid corotation. The Titan data, taken while the moon was inside the Saturn magnetosphere, shows a clear signature characteristic of the interaction between a subsonic corotating magnetospheric plasma and the atmospheric or ionospheric exosphere of Titan.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 212; Apr. 10
    Format: text
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  • 17
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    No evidence of rings around Neptune (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The results of two observations of stellar occultations of Neptune to determine if the planet has a ring system are reported. The sightings were made from Mt. Stromlo, Mauna Kea, and Cerro Tololo, noting that an equatorial ring would subtend only two arcsec of view. An upper accretion limit was defined to set the region around Neptune where rings, rather than satellites, could form. The intensities of the starlight from the two selected stars were recorded by photometers on magnetic tape during the occultation period. One of the stars did not occult, but passed through the entire region where a ring system might be present. No definitive evidence for rings was found, although an optical depth for a Neptunian ring was calculated at 0.07, with a width of more than 5 km and a radius of 31,400 km.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature; 294; Dec. 10
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  • 18
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    Saturn's E ring (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Observations of the tenuous E ring of Saturn made by an earth-based CCD system at the time of the ring-plane crossing of March 1980 are presented. The observations were made with the CCD system attached to the 1.8-m Perkins reflector at Lowell Observatory using a pupil mask behind a focal plane mask to suppress telescopic diffraction. Photometric analysis of the CCD images reveal the edge-on brightness profile of the ring, beginning at a distance of 3 Saturn radii, to peak sharply in the vicinity of the orbit of Enceladus at about 4 Saturn radii, then decrease to a distance of over 8 Saturn radii. In addition, beyond Enceladus, the edge-on width of the ring is observed to increase with radial distance, reaching nearly 5 arcsec at 7 Saturn radii. Observations suggest, on the one hand, that the E ring is associated with Enceladus and possibly represents material ejected from the satellite, and on the other, that the ring is at an early stage in its evolution.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 47; July 198
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  • 19
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    Voyager search for posteclipse brightening on Io (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Results of Voyager observations intended to settle the question of the transient brightening of the Io disk after its emergence from the Jovian shadow are presented. Two observation sequences were obtained on each Voyager flight through the violet filters of the Narrow Angle Cameras at frame intervals of 96 sec. No posteclipse was detected in the disk-integrated brightnesses in any of the sequences to within a few percent accuracy for a time span of up to 30 min following eclipse reappearance. Analysis of several representative individual areas on the disks of Io and Europa confirms the full-disk observations and is in contrast to telescopic observations showing a brightening of 10% just after eclipse which disappears on a time scale of 20 to 15 min. A small amount of brightening lasting about 3 min is found in the south polar region, along with some posteclipse darkening in neighboring regions. Observations imply that yellow sulfur (S8), the reflectance of which changes significantly over the eclipse temperature range, can not be a major constituent of the Io surface, and that the atmospheric column density of SO2 must be significantly less than 0.2 cm-atm at local noon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 47; July 198
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  • 20
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    Parametric interaction and spatial collapse of beam-driven Langmuir waves in the solar wind (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations are presented of the parametric decay and spatial collapse of Langmuir waves driven by an electron beam streaming into the solar wind from the Jovian bow shock. Long wavelength Langmuir waves upstream of the bow shock are effectively converted into short wavelength waves no longer in resonance with the beam. The conversion is shown to be the result of a nonlinear interaction involving the beam-driven pump, a sideband emission, and a low level of ion-acoustic turbulence. The beam-driven Langmuir wave emission breaks up into a complex sideband structure with both positive and negative Doppler shifts. In some cases, the sideband emission consists of isolated wave packets with very short duration bursts, which are very intense and are thought to consist of envelope solitons which have collapsed to spatial scales of only a few Debye lengths.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: AD-A107217 , Journal of Geophysical Research; 86; Sept. 30
    Format: text
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