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Horn, L. J.

Publications and source records attributed to Horn, L. J..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Detection and Behavior of Pan Wakes in Saturn's A Ring

Six previously unseen Pan wakes are found interior and exterior to the Encke gap in Saturn's A ring, one in the Voyager 2 photopolarimeter (PPS) stellar occultation data and five in the Voyager 1 radio science (RSS) Earth occultation data. Pan orbits at the center of the Encke gap and maintains it...The detection of Pan wakes at longitudes greater than 360(deg) demonstrates that wakes persist for much longer than originally hypothesized and may interact with one another.

planetary rings rings of saturn voyager spacecraft↗
NASA NTRS1995

Surficial Iron Conversion Mechanisms for the Surface of Mercury

The spectral evidence for the presence of iron on the surface of Mercury is equivocal. Estimates of strength of the 0.9 to 1.2 micron coordination band range from weak to non-existent. This band provides a measure of iron bound in pyroxenes, feldspars and olivine. This band is ubiquitous for spectra of Earth, the Moon, and Mars. It is reasonable to believe that Mercury would have similar total iron.

Mercury iron planetary geology planetary geophysic↗
NASA NTRS1994

Hermes Global Orbiter: A Discovery Mission in Gestation

The hermes Global Orbiter (HGO) is a Discovery class mission under study, which is investigating the possibility of placing a small spacecraft in highly elliptical polar orbit about mercury. The purpose of the mission is to conduct observations of the planet's surface, atmosphere and magnetosphere.

spacecraft Mercury orbit payload Delta II Venus fl↗
NASA NTRS1993

Mass of Saturn's A ring

The mass of Saturn's A ring is reestimated using the behavior of spiral density waves embedded in the ring. The Voyager photopolarimeter (PPS) observed the star delta-Scorpii as it was occulted by Saturn's rings during the Voyager 2 flyby of Saturn in 1981 producing a radial profile of the rings. We examined forty spiral density waves in the Voyager PPS data of the A ring including 10 weaker waves that have not been previously analyzed by means of an autoregressive power spectral technique called Burg. The strengths of this new method for ring studies are that weaker, less extended waves are easily detected and characterized. This method is also the first one which does not require precise knowledge of the resonance location and phase of the wave in order to calculate the surface mass density. Uncertainties of up to 3 km are present in the currently available radial scales for Saturn's rings.

Horn, L. J.↗
NASA NTRS1990

Spectral geometric albedo and bolometric Bond albedo of Neptune's satellite Triton from Voyager observations

The spectral geometric albedo and the bolometric Bond albedo of Triton are calculated using data from the Voyager spacecraft photopolarimeter and science experiments. The geometric albedo is not inconsistent with the presence of a weak absorption feature in Triton's spectrum near 0.75 micron. The bolometric Bond albedo (0.65) is consistent with the 38 K daytime surface temperature of Triton. The results are also in agreement with the 37.5 K temperature of nitrogen at an infrared basal pressure of 14 microbar.

Nelson, R. M.↗
NASA NTRS1990

Voyager photopolarimeter observations of Uranian ring occultations

Occultation profiles have been derived from Voyager 2 photopolarimeter observations of the nine pre-Voyager Uranian rings as well as of 1986U1R. The epsilon ring, which is the broadest and most massive, is noted to possess a wealth of structure which appears to persist coherently around the ring. The photopolarimeter data do not show any features globally ascribable to all the rings observed. Results are presented from a statistical analysis of photopolarimeter data for previously undetected or partial ring arcs.

Colwell, Joshua E.↗
NASA NTRS1988

Physical properties of Uranian delta ring from a possible density wave

On the basis of wavelength and amplitude behavior, as well as observed feature morphology, that are indicative of a density wave, the presently studied Voyager PPS stellar occultation observations of the Uranus delta ring are held to indicate the presence of a moonlet interior to the delta ring. Lindblad resonances are calculated for all 65 discrete possible locations for this moonlet; the locations are labeled by azimuth number of the resonance associated with each location that would excite the observed density wave in the delta ring.

Horn, L. J.↗
NASA NTRS1986

Photometry from Voyager 2 - Initial results from the Uranian atmosphere, satellites, and rings

The results of Voyager 2 photopolarimetry (PPS) surveys of Uranus, the ring system, occultation experiments and observations of the Uranian moons are reported. Dual-channel photometry and polarimetry data obtained of the atmosphere at various emission and phase angles are delineated and compared with characteristics of the Saturn and Jupiter atmospheres. The results of temperature, UV absorption and density profile calculations are also discussed. Extensive ring dimensional data, based on two occultation experiments, are provided in tabular form noting that the rings contain no dust. Finally, the geometric albedos of the five major moons and the phase curve of the moon Titania are presented. The latter data indicate that Titanian surface features are not the result of recent events such as volcanism or ice slurry outflows.

Lane, A. L.↗
NASA NTRS1984

Evidence for material between Saturn's A and F rings from the Voyager 2 photopolarimeter experiment

The region in the Saturn system between the F ring and the outer edge of the A ring is an area that appears, in images from the imaging experiment, to be virtually devoid of material except for three small satellites. Near the orbit of 1980S28, Atlas - the innermost satellite - the Voyager Photopolarimeter Stellar Occultation data show a discontinuity in count rate which marks a boundary between the tenuous material near the outer edge of the A ring and the orbit of Atlas. The data pertaining to this region have been examined with the aid of statistics and models generated from other similar ring structures. It is concluded that the discontinuity is real, implying the existence of tenuous material of normal optical depth of 0.01 to 0.006 in this region.

Graps, A. L.↗