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Owen, T.

Publications and source records attributed to Owen, T..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Tentative confirmation of an aurora on Uranus

There have been three recent reports of the detection of Lyman-alpha radiation (due to atomic hydrogen, H, at wavelength 1,216 A) from Uranus by means of the International Ultraviolet Explorer (IUE) satellite. The interpretations of these results differ. Two reports conclude that there is a strong aurora on Uranus, but the third concludes that the source is resonance scattering of solar Lyman-alpha. This paper reports the detection of emission features due to molecular hydrogen, H2, near 1,600 A. This detection is near the limit of the IUE sensitivity. If it is real, the detection of H2 emission strongly supports the conclusion that Uranus has an aurora comparable in strength with those of the inner two giant planets, Jupiter and Saturn. The first published IUE spectra of the Saturn aurora are also presented.

Caldwell, J.↗
NASA NTRS1982

Laboratory band strengths of methane and their application to the atmospheres of Jupiter, Saturn, Uranus, Neptune, and Titan. II - The red region 6000-7600 A

Lutz et al. (1976) have reported the first quantitative analyses of the strengths of the blue-green bands of methane which dominate the visible spectra of the outer planets. The present investigation represents an extension of the first study to include a number of bands between 6000 and 7500 A. The objective of this extension is to establish the validity of the scaled numerical curve of growth of the first study further into the saturated region and to test the apparent pressure independence of the high-overtone bands over a large pressure range. In addition, it is desired to provide a set of homogeneously determined band strengths and curves of growth over a large spectral region and over a large range of band strengths. This will make it possible to investigate feasible apparent dependences of planetary methane abundances on wavelength and band strength as a probe of the scattering processes in the planetary atmospheres.

Lutz, B. L.↗
NASA NTRS1982

Tita: discovery of carbon monoxide in its atmosphere

The 3-D rotation-vibration band of carbon monoxide was identified in the near-infrared spectrum of Titan. A preliminary mixing ratio of CO/N2 = 0.00006 was determined. This result supports the probable detection of CO2 by Samuelson et al and strengthens possible analogies between the atmosphere of Titan and conditions on the primitive Earth.

Lutz, B. L.↗
NASA NTRS1981

Colors on Jupiter

The colors present in the clouds of Jupiter at the time of the Voyager encounters are described as they appear in high resolution images. It is shown that latitude, altitude and dwelltime are all critical factors in determining which colors appear where, although the identities of the responsible chromophores remain unestablished. Simultaneous ground-based 5 micron observations are used to determine the relative altitudes of the cloud systems which are characterized as white clouds, tawny clouds, dark brown cloud belts, and blue-grey hot spots in equatorial regions. Correlations between cloud color and certain latitudes have been maintained for decades, which suggests the importance of the internal energy source.

Owen, T.↗
NASA NTRS1981

On the possible detection of CH3D on Titan and Uranus

The possible spectral detection of monodeuterated methane, CH3D, in the atmospheres of Titan and Uranus is reported. The detection was made on the basis of the identification of a new band centered near 6425 per cm in laboratory spectra of CH3D, which could possibly account for the strength of the methane absorption near 6400 per cm observed in the interferometric spectra of Titan and Uranus of Fink and Larson (1979). On the basis of measurements of the CH3D/CH4 natural abundance ratio and the estimated band strength of the 6425 per cm band, it is concluded that approximately 15% of the observed methane absorption is due to CH3D, rather than a pure temperature effect in CH4.

Lutz, B. L.↗
NASA NTRS1981

Implications of Titan's north-south brightness asymmetry

Voyager 1 images of Titan, when normalized to remove limb darkening, reveal an axially symmetric brightness pattern with significant north-south asymmetry. This interhemispheric contrast seems to be a response to seasonal solar heating variations resulting from Titan's inclined spin axis. The contrast significantly lags the solar forcing, indicating that its production involves the atmosphere well below the unit optical depth level. The contrast has a significant effect on Titan's disk-integrated brightness as seen from earth, and probably accounts for most of the observed long term variation, with solar UV variations accounting for the remainder.

Sromovsky, L. A.↗
NASA NTRS1981

Behavior of Titan's atmosphere during a total eclipse

During its emergence from the Saturnian shadow on June 28, 1980, Titan was observed simultaneously in the visible and IR ranges (6000-9000 A, and 11.8 and 20 microns). The eclipse observation indicates that thin-atmosphere models with a modest greenhouse effect are likely to be incorrect. A thin atmosphere of pure methane in equilibrium with an ice surface of methane is in marginal agreement with the present data, but improved VLA temperature measurements would be a crucial test of this model. Both the eclipse observation and VLA measurements agree with a nitrogen-dominant atmospheric model, as indicated by preliminary Voyager results.

Combes, M.↗
NASA NTRS1981

Observations of Uranus, Neptune, and Titan by the International Ultraviolet Explorer

The ultraviolet spectra of Uranus, Neptune, and Titan do not reveal absorption features at 7-A resolution from 2100 to 3200 A. Upper limits of from 1 to 3 A are set for the equivalent widths of narrow absorptions, which corresponds to a CO/H2 mixing ratio less than 2 x 10 to the -4th in the case of Uranus. The slopes of the continuum reflectivities of Uranus and Neptune are consistent with the semi-infinite Rayleigh-Raman scattering model of Cochran, while the absolute levels are matched only if solar photometry is modified within acceptable limits. An alternative, but less satisfactory explanation of the new data is that the UV reflectivities of both Uranus and Neptune are depressed uniformly by a continuum absorber. The suggestion by Savage et al (1980) that the albedo of Uranus decreases by approximately 20% from 2200 to 1800 A is not confirmed. For Titan, the albedo decreases monotonically toward shorter wavelengths down to 2300 A. New limits are set for the pressure level in the atmosphere of Titan up to which the real, but presently unidentified, UV absorber there must extend, and for the fraction of Titan that must be covered by this absorber

Caldwell, J.↗
NASA NTRS1980

First Voyager view of the rings of Saturn

Voyager 1 imaging data of the Saturn rings, taken at a resolution of 1000 km/line pair between September 3 and October 13, 1980 are discussed. It is pointed out that as the spacecraft approached Saturn, finer radial structure in the rings between and within the major divisions became apparent, together with extensive azimuthal structure in the B ring. It is shown that the fine structure observed in the rings cannot, for the most part, be attributed to classical resonances with the known inner satellites. Preliminary model calculations of ring brightness based on photometry data indicate that the particles of the A and B rings are characterized by a greater degree of diffuse backscattering ability than previously suspected, behaving like Lambert spheres, while those of the C ring are either darker or more highly forward scattering than the A or B ring particles.

Collins, S.A.↗
NASA NTRS1980

Radius and brightness temperature observations of Titan at centimeter wavelengths by the Very Large Array

Brightness and radius measurements of the surface of Titan at 6, 2, and 1.3 cm wavelengths obtained with the Very Large Array radio interferometer are presented. Combined results for the three wavelengths indicate that the radius is 2400 + or - 250 km, implying a density of 2.4 + or - 0.7 g/cu cm, and that the brightness temperature is 87 + or - 9 K. The surface temperature may be somewhat higher if the emissivity is less than unity. The new data do not permit a choice between an inversion model for the atmosphere of Titan that predicts a surface temperature of 78 K and a model with both a stratospheric temperature inversion and a modest greenhouse effect that would increase the surface temperature by 10-40 K.

Jaffe, W.↗
NASA NTRS1980

Lyman-alpha observations in the vicinity of Saturn with Copernicus

For the first time, high-resolution Ly-alpha observations of the Saturn vicinity were completed with the Princeton spectrometer on board the Copernicus satellite. They showed that near a minimum solar activity the emissions related to several sources are 250 + or - 50 rayleighs for the interplanetary medium in a near-downwind direction, less than 100 rayleighs for the rings, 200 + or - 100 rayleighs for a torus linked to the Titan orbit, and 1400 + or - 450 rayleighs for the disk of Saturn. These results induce some constraints through the corresponding theoretical evaluations: the B ring as the primary source of the atoms for the ring emissions; an efficient production mechanism for hydrogen atoms in the Titan torus; and a slightly larger eddy diffusion coefficient in the Saturn atmosphere than in the Jupiter atmosphere near solar minimum.

Barker, E.↗
NASA NTRS1980

An upper limit to the global SO2 abundance on Io

An upper limit to the global abundance of SO2 gas in the atmosphere of Io has been derived from observations of near-UV reflectivity made from earth orbit. Spectra in the range 2900-3100 A were obtained by the long-wavelength spectrograph of the IUE, and compared with the convolved solar spectrum of Broadfoot (1972). From the apparent solar origin of all the spectral features, an upper limit of 0.008 cm atm was calculated for the abundance of SO2, which was confirmed by ratio spectra of Vesta. Discrepancies between the upper limit obtained and the detection of a column abundance of 0.2 cm atm by the Voyager 1 IRIS experiment have a number of possible explanations, the most likely of which is that the SO2 atmosphere in Io is patchy, being confined to regions over solid deposits and volcanic vents.

Butterworth, P. S.↗
NASA NTRS1980

Observations of the spectrum of Jupiter from 1500 to 2000 A with the IUE

The paper examines the far-UV spectrum of Jupiter recorded by observations with the International Ultraviolet Explorer, noting that only the upper levels of the plant's atmosphere are sampled. It is shown that there are several absorptions caused by C2H2 and indications that NH3 may also be present at these altitudes. In addition, it is suggested that PH3 may also play a role as a continuum absorber, and a new upper limit of 5 x 10 to the -9 on H2S/H2 forbidden line ratio. It is concluded that these results are consistent with existing models for Jovian photochemistry and atmospheric structure.

Owen, T.↗
NASA NTRS1980

The Martian paleoclimate and enhanced atmospheric carbon dioxide

Current evidence indicates that the Martian surface is abundant with water presently in the form of ice, while the atmosphere was at one time more massive with a past surface pressure of as much as 1 atm of CO2. In an attempt to understand the Martian paleoclimate, a past CO2-H2O greenhouse was modeled and global temperatures which are consistent with an earlier presence of liquid surface water are found in agreement with the extensive evidence for past fluvial erosion. An important aspect of the CO2-H2O greenhouse model is the detailed inclusion of CO2 hot bands. For a surface pressure of 1 atm of CO2, the present greenhouse model predicts a global mean surface temperature of 294 K, but if the hot bands are excluded, a surface temperature of only 250 K is achieved.

Cess, R. D.↗
NASA NTRS1979

The Martian atmosphere - Some unanswered questions

The study of the Martian atmosphere and its significance for the possible origin of life on Mars is still very incomplete. Further investigations are needed to define the total volatile inventory, the early history of the atmosphere, and the relationship of the atmosphere to the question of indigenous life. In addition, studies of Venus, comets, and the Jupiter system will add significantly to our abilities to understand the early history of Mars.

Owen, T.↗
NASA NTRS1979

Jupiter's rings

Voyager 2 observations of the jovian ring system discovered by Voyager 1 are presented. The rings were observed both above and below the jovian equatorial plane and at extremely low and high phase angles. This ring system seems to represent a steady state configuration for small particles that are slowly moving in toward Jupiter. It must be resupplied from sources well outside Roche's limit.

Owen, T.↗