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Caldwell, J. J.

Publications and source records attributed to Caldwell, J. J..

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

International Jupiter Watch - A program to study the time variability of the Jovian system

The International Jupiter Watch is a program for the encouragement and coordination of the study of temporal variations in the Jovian system. It consists of six discipline working groups concerned with: the Io torus under N. Schneider; the Jovian atmosphere under R. West; the magnetosphere and radio emissions under I. de Peter and M. Klein; aurora under J. Caldwell; the Galilean satellites under W. Sinton and J. Goguen; and laboratory measurement and theory under B. Lutz. To date the IJW has held two workshops and selected several Jupiter Watch periods for coordinated observations. The next Jupiter Watch workshop is tentatively scheduled for 1990 in association with the next COSPAR meeting.

Russell, C. T.↗
NASA NTRS1984

Restored methane band images of Uranus and Neptune

Charge-coupled device images of Uranus and Neptune taken in the 8900-A absorption band of methane are presented. The images have been digitally processed by means of nonlinear deconvolution techniques to partially remove the effects of atmospheric seeing. The restored Uranus images show strong limb brightening consistent with previous observations and theoretical models of the planet's atmosphere. The computer-processed images of Neptune show discrete cloud features similar to those reported previously by Smith, Reitsema, and Larson (1979). A time series of the restored Neptune images shows a continuous variation which may be due to the planet's rotation.

Heasley, J. N.↗
NASA NTRS1984

Composition and chemistry of Saturn's atmosphere

A comprehensive discussion and review is presented of the chemistry and composition of Saturn as determined by earth-based, earth-orbital, and Voyager 1 and 2 spectroscopic observations. The observations imply that there are important differences between the actual composition of Saturn's atmosphere and that predicted for a homogeneous solar-composition planet. The H2, He, Ch4, NH3, and PH3 volume mixing ratios differ from the expected solar composition ratios, implying that during its formation Saturn accreted a significant amount of ice and rock. The depletion of He in the visible atmosphere suggests that this element has preferentially differentiated toward the center of the planet. The D to H ratio is similar to that on Jupiter and has important cosmological implications. Volume mixing ratios for C2H6 and C2H2 are consistent with the theoretically expected photochemical sources for these gases.

Prinn, R. G.↗
NASA NTRS1974

Ultraviolet observations of Titan from OAO-2

High altitude deposition of energy in Titan's atmosphere can have a significant effect on the spectral distribution of emitted thermal radiation from the satellite. This reasoning led to the prediction of emission peaks at wavelengths corresponding to allowed bands of CH4 and trace photolysis products such as C2H6. Intermediate resolution infrared spectrophotometry has encouraged this interpretation of the infrared properties of Titan, and provided the basis for initial, detailed model.

Caldwell, J. J.↗
NASA NTRS1974

An inversion in the atmosphere of Titan

A very detailed greenhouse model derives a methane to hydrogen ratio of unity and a minimum surface pressure of 0.4 atm. Based on a surface gravity g = 140 cm sec/2, the minimum CH4 abundance is 30-40 km-A and the minimum H2 abundance varies from 15 to 85 km-A. A model of the atmosphere of Titan is proposed which seems to be consistent with observations and requires a much smaller CH4 abundance (of the order or 2 km-atm). Although no H2 is required, the presence of some H2 is readily accommodated. In this model, a temperature inversion exists in the atmosphere due to absorption of blue and ultraviolet solar radiation by small particles. The absorbed radiation is re-radiated by the dust and by molecules having long wavelength bands such as CH4 7.7 micrometer and ethane at 12.2 micrometer. The brightness temperature at 20 micrometer is primarily due to re-radiation by the dust.

Danielson, R. E.↗
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 NTRS1973

Test facility for 6000 hour life test of 30 cm mercury ion thruster

The environmental and instrumentation requirements for long term testing of electrical propulsion thrusters which impose severe and unusual requirements upon the simulation facility were studied. High speed ions ejected from a mercury thruster erode material from collecting surfaces, which is then scattered and redeposited upon other surfaces, with resultant damage to the chamber and test article. By collecting the thruster plume on a frozen mercury surface damage to the thruster and chamber by back-scattered erosion products was minimized. Provisions for unattended operation, remote data acquisition, personnel safety, and instrumentation for assessing thruster performance are also discussed.

Caldwell, J. J.↗
NASA NTRS1972

Ultraviolet photometry from the orbiting astronomical observatory. III - Observations of Venus, Mars, Jupiter, and Saturn longward of 2000 A.

A number of high-quality spectra of Mars, Jupiter, the combined disk and rings of Saturn, as well as lower-quality spectra of Venus, have been obtained with an objective-grating spectrometer of the Wisconsin Experiment Package of OAO-2. An intercomparison of the Mars, Jupiter, and Saturn spectra has failed to disclose any discrete planetary absorptions. Continuous albedos have been derived for the four planets by using OAO-2 observations of G-type stars for wavelengths greater than 2700 A. The geometric albedo of Mars shows a steady increase below 3500 A which appears to be due to Rayleigh scattering combined with a decreasing surface reflectivity. The albedos of Venus, Jupiter, and Saturn show a maximum in reflectivity in the region of 2500 A.-

Wallace, L.↗
NASA NTRS1972

Observations of Venus, Mars, Jupiter and Saturn longward of 2000 A

A number of high quality spectra of Mars, Jupiter, the combined disk and rings of Saturn, as well as lower quality spectra of Venus, have been obtained with an objective grating spectrometer of the Wisconsin experiment package on OAO-2. An intercomparison of the Mars, Jupiter and Saturn spectra has failed to disclose any discrete planetary absorptions. Continuous albedos have been derived for the four planets by using OAO-2 observations of G-type stars for wavelengths greater than 2700 A and a new photoelectric solar spectrum for wavelengths smaller than 2700 A. The geometric albedo of Mars shows a steady increase below 3500 A which appears to be due to Rayleigh scattering combined with a decreasing surface reflectivity. The albedos of Venus, Jupiter and Saturn show a maximum in reflectivity in the region of 2500 A.

Wallace, L.↗