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  • LUNAR AND PLANETARY EXPLORATION  (737)
  • ASTROPHYSICS  (589)
  • 1980-1984  (1,326)
  • 1
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    Disappearing ionospheres on the nightside of Venus (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Instruments on the Pioneer Venus Orbiter have detected a substantial ionosphere on the nightside of Venus during most orbits. However, during some orbits the nightside ionosphere seems to have almost disappeared, existing only as irregular patches of low-density plasma. The solar wind dynamic pressure on these occasions is greater than average. Data from several instruments (Langmuir probe, ion mass spectrometer, retarding potential analyzer, magnetometer, and plasma analyzer) have been correlated for a number of orbits during which the nightside ionosphere had disappeared. The magnetic field tends to be coherent, horizontal, and larger than usual, and the electron and ion temperatures are much larger than they usually are on the nightside. Mechanisms are suggested which might explain the reasons for the disappearance of the ionosphere when the solar wind dynamic pressure is large.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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    NASA TECHNICAL REPORTS
  • 2
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    Photometry and polarimetry of Saturn at 2640 and 7500 A (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Voyager 2 photometric and polarimetric data are reduced and tabulated, with spatially resolved limb-to-terminator scans across Saturn's equatorial zone providing information on the altitude distribution of UV-absorbing hazes, together with the phase function and polarizing properties of stratospheric and tropospheric aerosols. It is found that the UV photometry and polarimetry are best fit by Rayleigh's phase matrix. A stratospheric haze of small particles is allowed as long as the optical depth is near unity or less, and the center of the haze layer is in the 30 to 70 mbar region. The altitudes presently derived for three latitudes agree with those obtained by ground-based methane band studies and analyses from Pioneer 11. A high altitude absorber is abundant in the polar regions.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 88; 8679-869
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    NASA TECHNICAL REPORTS
  • 3
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    Photopolarimetry from Voyager 2 - Preliminary results on Saturn, Titan, and the rings (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The Voyager 2 photopolarimeter was reprogrammed prior to the August 1981 Saturn encounter to perform orthogonal-polarization, two-color measurements on Saturn, Titan, and the rings. Saturn's atmosphere has ultraviolet limb brightening in the mid-latitudes and pronounced polar darkening north of 65 deg N. Titan's opaque atmosphere shows strong positive polarization at all phase angles (2.7 deg to 154 deg), and no single-size spherical particle model appears to fit the data. A single radial stellar occultation of the darkened, shadowed rings indicated a ring thickness of less than 200 meters at several locations and clear evidence for density waves caused by satellite resonances. Multiple, very narrow strands of material were found in the Encke division and within the brightest single strand of the F ring.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 215; Jan. 29
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  • 4
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    Molecular Clouds Within 100 Pc (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-16
    Description: Observations at the 2.6 mm line of CO reveal the presence of a large number of molecular clouds at high galactic latitude. If the velocity dispersion of the clouds is a measure of their scale height, the mean distance of the ensemble detected is 100 pc. The clouds are unusual in that either they are not gravitationally bound or they are very deficient in CO relative to molecular hydrogen. These clouds represent a heretofore unrecognized component of the local interstellar medium. If they are pervasive in the Milky Way, they probably represent the small molecular cloud component of the interstellar medium.
    Keywords: ASTROPHYSICS
    Type: NASA. Goddard Space Flight Center Local Interstellar Medium, No. 81; p 231-234
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  • 5
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    Imaging photopolarimeter on Pioneer Saturn (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Results of Pioneer 11 imaging photopolarimeter observations of Saturn, its rings, and Titan are presented. The imaging photopolarimeter is a pointable telescope with an aperture of 2.5 cm and passbands of 390 to 500 to 720 nm which uses the spin of the spacecraft to scan across an object. Images of the Saturn system and of the rings are presented, and the absence of a D ring, structures in the C, B and A rings and the Cassini division and the discoveries of the F ring and the provisionally named Pioneer division separating it from the A ring are reported. A mean particle size less than 15 meters is estimated from estimates of total ring mass and the optical depth of the B ring. The discovery of the satellite 1979 S 1 at 2.53 Saturn radii is also noted. Models of the vertical aerosol structure of Saturn's atmosphere are compared with the polarization data, and it is indicated that the density of cloud particles decreases with altitude with a scale height about one fourth that of the gas, and that an optical depth of one is to be found at 750 mbar.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science; 207; Jan. 25
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  • 6
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    Pre-4.2 AE mare-basalt volcanism in the lunar highlands (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The discovery of a 4.23 AE, low-Ti composition mare basalt from the Fra Mauro Formation has challenged the hypothesis that the plutonism of the lunar highlands and the mare-type volcanism are two separate problems in both space and time. Attention is presently given to data indicating that non-KREEPy, mare-type volcanism began at least as early as 4.2 AE in the Fra Mauro region, and probably across much of the lunar surface. Massive bombardment during the 'terminal cataclism', and the subsequent veneer of younger mare basalts has obliterated most of the evidence for these ancient volcanic events, which may be related to such basin-forming events as the impact-triggered igneous activity that made Procellarum.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Earth and Planetary Science Letters (ISSN 0012-821X); 66; 33-47
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  • 7
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    The filaments of NGC 1275 - A collision between a galaxy and an accretion flow? (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Morphological evidence is presented (in the form of 3-A-bandpass Fabry-Perot images made with a CCD camera) that the two bright emission-line systems seen toward the galaxy NGC 1275 arise from a high-velocity impact of a foreground galaxy upon the accretion flow of gas cooling in the center of the Perseus cluster. The uniquely high optical-line luminosity of NGC 1275, in comparison with other central galaxies in clusters observed to have cooling flows, may be explained by energy deposited during the collision. Using additional information from 21-cm and extinction measurements, a rough model of the interaction is developed. Problems remain with this model - such as the likelihood of a gas-rich system penetrating to the cluster center. The kinematic structure of the optically emitting gas shows additional complex structure near the nucleus of NGC 1275.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 275; L27-L31
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  • 8
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    Coordinated Einstein and IUE observations of a disparitions brusques type flare event and quiescent emission from Proxima Centauri (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The Einstein Imaging Particle Counter observed a major X-ray flare in its entirety during a 5-hr period of simultaneous observations, with the IUE, of the dM5e flare star Proxima Centauri in August, 1980. The detailed X-ray light curve, temperature determinations during various intervals, and UV line fluxes obtained before, during, and after the flare indirectly indicate a 'two-ribbon flare' prominence eruption. The calculated ratio of coronal to bolometric luminosity for the event is about 100 times the solar ratio. The Proxima Cen corona is analyzed in the context of static loop models, in light of which it is concluded that less than 6% of the stellar surface seems to be covered by X-ray emitting active regions.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 267
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  • 9
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    Hercules X-1 hard X-ray pulsations observed from HEAO 1 (1980)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The 1.24-sec pulsations of Her X-1 in the energy range 13-75 keV have been analyzed in data obtained from the UCSD/MIT experiment on HEAO 1 during observations of the source on three dates in February 1978 and three in August 1978. Observational results are (1) the main pulse broadens somewhat with increasing energy; (2) the pulsation light curve undergoes pronounced changes at the leading edge of the main pulse from day to day; (3) spectral hardening within the main pulse is confirmed; (4) a 40-60 keV spectral feature in the spectrum is confirmed; (5) this feature is resolved, the pulse width broadening is greater than 20%, and its centroid varies with pulsation phase; and (6) the 13-75 keV spectrum does not noticeably vary from day to day, except for an overall intensity factor. Some implications of these results for the prevailing models of Her X-1 and the HZ Her-Her X-1 system are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 240
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  • 10
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    Observations of 12-200 keV X-rays from GX 339-4 (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: X-ray spectra of GX 339-4 measured on three occasions in 1977 and 1978 are presented. These are the first reported measurements above 10 keV. The spectra can be described as the superposition of a soft component, which is dominant below about 20 keV, and a hard component at higher energy. Simultaneous measurements at lower energy show that the soft component vanished during the observation in early 1978. The behavior of these two components is similar to that of the spectrum of Cygnus X-1; this reinforces the previously noted resemblance in rapid X-ray variability.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 262
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