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At least 109 records · Page 6
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NASA NTRS1974

Ultraviolet photometry from the Orbiting Astronomical Observatory. XIII - The albedos of Jupiter, Uranus, and Neptune

Presentation of OAO-2 broad-band ultraviolet photometry data for Jupiter, Uranus, and Neptune. These data have been combined with observations of 23 late-type stars to derive planetary albedos over the region 2000-4300 A. The new broad-band albedo for Jupiter agrees well with a previous measurement based on OAO-2 spectrometer data. The albedos for Uranus and Neptune are in good agreement with ground measurements in the region of overlap. The results for Uranus and Neptune have been compared with theoretical calculations for semiinfinite and finite pure H2 Rayleigh-Raman scattering atmospheres. Except for the shortest wavelengths, the measurements lie below the semiinfinite theoretical calculations. The calculations for the finite atmospheres suggest that an additional absorbing constituent will be needed to explain the observed albedos.

Savage, B. D.↗
NASA NTRS1975

Possible radio emission from Uranus at 0.5 MHz

Radio emission from the direction of Uranus was detected in data from the radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn was observed by the IMP-6 at a number of frequencies near 1 MHz during the period April 1971 to October 1972. These radio bursts were identified in the IMP-6 data through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of the planet Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics were found. Identification with Uranus is confused by the likely presence of low level terrestrial and solar emission. The observed events persisted less than three minutes and are strongest in intensity near 0.5 MHz.

Brown, L. W.↗
NASA NTRS1976

Methane rich models of Uranus

A series of models of Uranus is computed assuming that Uranus consists of a core of rocky material surrounded by a convecting envelope rich in H2O, NH3, and CH4. It is found that good fits are obtained to the observed parameters when the CH4:H2 ratio is of the order of 0.1. It is suggested that the rotational period of Uranus is roughly 18 h.

Podolak, M.↗
NASA NTRS1976

Possibility of detecting magnetospheric radio bursts from Uranus and Neptune

The intensity of magnetospheric radio bursts (MRBs) is scaled to solar-wind input into planetary magnetospheres and the frequency of emission is scaled to polar surface magnetic-field strength in order to estimate the possibility of detecting MRBs from Uranus and Neptune. A scaling law is derived which relates the ratio of power radiated in MRBs to the solar-wind input for earth, Jupiter, and Saturn. Power-flux spectra of MRBs from these three planets are plotted, and it is shown that Jupiter and Saturn may radiate 1% to 5% of the solar-wind energy input into their magnetospheres. The properties of MRBs from Uranus and Neptune are estimated by assuming a conversion efficiency of 1% to 5%, a bandwidth of half the peak frequency, and conformity of Uranus' and Neptune's dipole moments with the magnetic Bode's law. Based on the results, it is suggested that detection of MRBs from these two planets may be a reasonable cruise-mode radio-astronomy objective on future missions to the outer solar system.

Kennel, C. F.↗
NASA NTRS1977

Uranus occults SAO158687

Experience gained in obtaining atmospheric parameters, oblatenesses, and diameters of Jupiter and Mars from recent stellar occultations by these planets is used to predict what can be learned from the March 1977 occultation of the star SAO158687 by Uranus. The spectra of this star and Uranus are compared to indicate the relative instrument intensities of the two objects, the four passbands where the relative intensities are most nearly equal are listed, and expected photon fluxes from the star are computed on the assumption that it has UBVRI colors appropriate for a K5 main-sequence object. It is shown that low photon noise errors can be achieved by choosing appropriate passbands for observation, and the rms error expected for the Uranus temperature profiles obtained from the occultation light curves is calculated. It is suggested that observers of this occultation should record their data digitally for optimum time resolution.

Elliot, J. L.↗
NASA NTRS1977

The rings of Uranus

A description is given of the observation of five brief occultations of the star SAO 158687 which occurred both before and after its occultation by Uranus on March 10, 1977. The events were observed with a three-channel occultation photometer, attached to a 91-cm telescope. The observations indicate that at least five rings encircle the planet Uranus. Possible reasons for the narrowness of the Uranus rings are discussed.

Elliot, J. L.↗
NASA NTRS1977

Detection of rings around Uranus

A description is presented of partial occultations of SAO 158687 by a series of rings around the planet Uranus. A 61-cm telescope at Perth Observatory in Western Australia was used in the investigations. Measurements were made using a conventional single-channel photometer equipped with an RCA C31034B photomultiplier. Uranus was centered in a 28-arc sec diameter aperture during the observations. An occultation of SAO 158687 by Uranus itself did not occur at Perth. However, five brief partial occultations of SAO 158687 were detected with the chart recorder. The midtimes, durations, and depths of these events are listed in a table.

Millis, R. L.↗
NASA NTRS1977

The rotation of Uranus

The rotation rate of Uranus is investigated by measuring the tilts of reflected Fraunhofer lines observed through a slit spectrograph. The data obtained are corrected for the effect of astronomical seeing, and the data-reduction procedures are outlined in detail. Observations are discussed which indicate that the planet's pole of rotation is parallel to the pole of its satellites' orbits and that Uranus may not rotate as a solid body. A rotational period of 15.57 + or - 0.80 hr is derived for northern midlatitudes on Uranus by adopting a planetary diameter of 51,800 + or - 600 km. Possible sources of small systematic errors are briefly considered.

Brown, R. A.↗
NASA NTRS1978

Detection of HD on Saturn and Uranus, and the D/H ratio

The HD 5-0 R(0) line on Saturn and Uranus has been observed. Values for the D/H abundance ratio computed from models for the atmospheres of these two planets are 5.5 + or - 2.9 times 10 to the minus fifth power for Saturn and 3.0 + or - 1.2 times 10 to the minus fifth power for Uranus. The D/H ratio for Jupiter of 5.1 + or - 0.7 times 10 to the minus fifth power found from a measurement of the HD 4-0 P(1) line is bracketed by the values found for Saturn and Uranus.

Macy, W., Jr.↗
NASA NTRS1978

Far-infrared observations of Uranus, Neptune, and Ceres

During a single flight of our 102 cm balloon-borne telescope and 40-250 micron photometer we observed Uranus, Neptune, Ceres, Venus, Mars, and Saturn. Effective temperatures for Uranus (58.5 plus or minus 2 K) and Neptune (59.7 plus or minus 4 K) were determined, thus confirming the absence of a substantial internal heat source for Uranus and the presence of one for Neptune. Ceres has a brightness temperature of 195 plus or minus 12 K at an effective wavelength of 60 microns.

Stier, M. T.↗
NASA NTRS1978

The rings of Uranus - Results of the 10 April 1978 occultation

Observations of the April 10, 1978, stellar occultation by the rings of Uranus are presented. Nine rings were observed, and their radii and widths are calculated. Rings eta, gamma, and delta are found to be most likely circular and coplanar, in agreement with previous analyses; the remaining rings are either noncircular or slightly inclined. The width of the epsilon ring is a linear function of its radius from the center of Uranus, projected onto the satellites' orbital plane; this suggests that it forms one continuous noncircular ring. The optical-depth profile of the epsilon ring has not changed significantly since March 1977. A model of this ring which fits all available observations adequately is that of a uniformly precessing Keplerian ellipse coplanar with the satellites' orbits. This model permits predictions of the radius and width of the epsilon ring for future occultations. The precession rate is used to determine J2 for Uranus, on the assumption that precession is caused solely by the planetary oblateness and not by satellite-ring interactions.

Nicholson, P. D.↗
NASA NTRS1979

Methane band limb-brightening on Uranus

Area scanner measurements of the brightness distributions of Uranus at 6300 and 7250 A are presented. At the former wavelength, which is characteristic of continuum radiation, the observed limb-darkening is consistent with the results of Stratoscope observations. At the latter wavelength, in the center of a strong methane absorption band, the planet shows substantial limb-brightening as has been reported by other investigators. The limb-brightening and geometric albedo of Uranus in this methane band can be explained in terms of a clear atmospheric model in which the methane partial pressure above the saturation level is equal to its equilibrium vapor pressure. This conclusion is relatively insensitive to the methane mixing ratio below the saturation level. The presence of a high-altitude, conservatively, isotropically scattering haze of optical thickness 0.1, such as that previously proposed as a possible cause of the 7250-A limb-brightening, would produce a geometric albedo at this wavelength that is substantially larger than the value observed for Uranus.

Pilcher, C. B.↗
NASA NTRS1979

The infrared spectra of Uranus, Neptune, and Titan from 0.8 to 2.5 microns

The paper combines the results of two projects that significantly augment previous studies: exploratory IR spectroscopic observations of Uranus, Neptune, and Titan using a 4-m telescope; and new long-path laboratory comparison spectra of methane at abundances appropriate for these planetary spectra. The observations of these previously unexplored spectral regimes provide new insights into the composition and structures of these atmospheres. The spectra of Uranus, Neptune, and Titan are discussed and analyzed from several complementary points of view. A number of specific topics are discussed in detail: methane abundance determinations, limitations in using the 3nu3 CH4 band at high abundances, upper limits to a number of molecules, implications from the pressure-induced spectrum of H2, and consequences of Rayleigh scattering in Uranus's upper atmosphere.

Fink, U.↗
NASA NTRS1980

The radius and ellipticity of Uranus from its occultation of SAO 158687

From occultation timings obtained from the Kuiper Airborne Observatory and from Cape Town for Mar. 10, 1977 occultation of SAO 158687 by Uranus, the equatorial radius, Re, of the planet has been determined to be 26,228 + or - 30 km and its ellipticity epsilon = 1 - Rp/Re = 0.033 + or - 0.007. These values refer to the 1.0 x 10 to the 14th/cu cm number-density level, under the assumption that the upper atmosphere is composed of H2 and He with a mean molecular weight mu = 2.20. The dominant source of uncertainty is the position of the center of the ring system, which was used to define the center of Uranus in our analysis. A rotation rate of 12.8 + or - 1.7 hours for the planet is implied by our value for the ellipticity, under the assumption that Uranus is in hydrostatic equilibrium below the 1.0 x 10 to the 14th/cu cm number density level.

Elliot, J. L.↗
NASA NTRS1980

Application of methane band-model parameters to the visible and near-infrared spectrum of Uranus

Laboratory band-model absorption coefficients of CH4 were used to calculate the Uranus spectrum from 5400 to 10,400 A. A good fit for both strong and weak bands for the Uranus spectrum over the entire wavelength interval was achieved; three atmospheric models were employed: (1) a reflecting layer model; (2) a homogeneous scattering layer model; and (3) a clear atmosphere sandwiched between two scattering layers. The spectrum for the reflecting layer model shows serious discrepancies but indicates that large amounts of CH4 are necessary to reproduce the Uranus spectrum. Both scattering models gave reasonably good fits; the homogeneous model requires a particle scattering albedo of at least 0.998 and an abundance per scattering mean free path of about 1 km-am. For the sandwich model, a continuum single scattering albedo of 0.995 was derived for the upper scattering layer, and the scattering optical depth variable wavelength was consistent with Rayleigh scattering.

Benner, D. C.↗
NASA NTRS1982

The rotation of Uranus

The determination of the rotation rate of Uranus based on available observational evidence is discussed. Previous determinations of the rotation rate since the work of Lowell and Slipher (1912), which tended to converge on a period of 10.8 days until the mid 1970s, most likely due to mutual reinforcement between unreliable results, are reviewed. Recent independent determinations based on (1) the use of theoretical interior models together with observations of oblateness and the gravitational moment J2; (2) periodic brightness fluctuations; and (3) spectrographic measurements of Doppler shifts are then presented which yield a weighted mean value of 16.31 + or - 0.27 h for the rotational period of Uranus. It is noted that the detection of the motion of surface features across the disk by future high-resolution imaging and Voyager 2 observations may allow a direct determination of the rotational period of Uranus.

Goody, R. M.↗
NASA NTRS1982

Rings of Uranus - A review of occultation results

The structure and orbits of the nine confirmed rings of Uranus are reviewed based on occultation observations from ring discovery in March 1977 through April 1981. Observations of stellar occultations by Uranus have revealed the rings to be characterized by narrow widths (up to 100 km) and sharp edges, with possible internal structure, and to have orbits fitting the coplanar precession model, and showing a decreasing eccentricity with semimajor axis. Occultation results have also allowed the determination of the J2 and J4 coefficients of the Uranian gravity potential, the coordinates of the ring plane pole, planetary equatorial radius and ellipticity and the rotation period. The sharp edges and narrow widths of the rings may be explained by small satellites orbiting near the rings, and the uniform precession of three of the rings is attributed to self-gravity. Future plans for Uranus ring observations include further occultation studies, the Voyager 2 fly-by, and Space Telescope data.

Elliot, J. L.↗
NASA NTRS1982

Possible occulations by satellites of Uranus and Neptune - 1983-1985

Predictions are presented for 15 possible occulations by the satellites of Uranus and Neptune from 1983 through 1985. Umbriel, the third satellite of Uranus, might occult a 10.4-mag star (Hyd-20 deg 51699) on 25 March 1983 which will be occulted by Uranus 14 hr earlier. Uncertainties in star positions and ephemerides of planets and satellites are quite large in comparison to the size of these bodies, and these predictions are to be taken as possibilities only.

Mink, D. J.↗