Planetary surfaces

Abstract:

The first four complete spectra recorded by the near infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft in 1996 have been analyzed. These spectra remain the only ones which have been obtained at maximum resolution over the entire NIMS wavelength range of 0.7 - 5.2 μm. The spectra cover the edge of a "warm" spot at location 5°N, 85°W. We have analyzed the spectra first with reflecting layer models and then with full multiple scattering models using the method of correlated-k. We find that there is strong evidence for three different cloud layers composed of a haze consistent with 0.5-μm radius tholins at 0.2 bar, a cloud of 0.75-lim NH3 particles at about 0.7 bar, and a two-component NH4SH cloud at about 1.4 bars with both 50.0- and 0.45-μm particles, the former being responsible for the main 5-μm cloud opacity. The NH3 relative humidity above the cloud tops is found to decrease slightly as the 5-μm brightness increases, with a mean value of approximately 14%. We also find that the mean volume mixing ratio of ammonia above the middle (NtL4SH) cloud deck is (1.7± 0.1) × 10-4 and shows a similar, though less discernible decrease with increasing 5-μm brightness. The deep volume mixing ratios of deuterated methane and phosphine are found to be constant and we estimate their mean values to be (4.9± 0.2) × 10-7 and (7.7 ± 0.2) × 10-7, respectively. The fractional scale height of phosphine above the 1 bar level is found to be 27.1± 1.4% and shows a slight decrease with increasing 5-μm brightness. The relative humidity of water vapor is found to be approximately 7%, but while this and all the previous observations are consistent with the assumption that "hot spots" are regions of downwelling, desiccated air, we find that the water vapor relative humidity increases as the 5-μm brightness increases. Copyright 1998 by the American Geophysical Union.

Abstract:

Vacuum glazing consists of two glass sheets with a narrow internal evacuated space. The separation of the sheets under the influence of atmospheric pressure is maintained by an array of small support pillars. The thermal resistances associated with the heat flow through individual pillars, and through the pillar array, are calculated using a simple analytic method, and by more complex finite element models. The results of both approaches are in very good agreement, and are validated by comparison with experimental data. It is shown that, for many purposes, the amount of heat which flows through the pillars can be determined without incurring significant errors by assuming that the heat flow is uniformly distributed over the area of the glass. Finite element modelling, and a superposition method, are used to determine the temperature distribution on the external surfaces of the glass sheets due to pillar conduction. Again the results obtained with both approaches are in very good agreement. An approximate method is described for calculating the magnitude of these temperature non- uniformities for all practical glazing parameters. Vacuum glazing consists of two glass sheets with a narrow internal evacuated space. The separation of the sheets under the influence of atmospheric pressure is maintained by an array of small support pillars. The thermal resistances associated with the heat flow through individual pillars, and through the pillar array, are calculated using a simple analytic method, and by more complex finite element models. The results of both approaches are in very good agreement, and are validated by comparison with experimental data. It is shown that, for many purposes, the amount of heat which flows through the pillars can be determined without incurring significant errors by assuming that the heat flow is uniformly distributed over the area of the glass. Finite element modelling, and a superposition method, are used to determine the temperature distribution on the external surfaces of the glass sheets due to pillar conduction. Again the results obtained with both approaches are in very good agreement. An approximate method is described for calculating the magnitude of these temperature non- uniformities for all practical glazing parameters.

Abstract:

Scientific results from NIMS observations of Venus have been extensively reported in the literature, while those of Jupiter have, at the time of writing, just barely commenced. The planning and interpretation of studies of these planets, with their massive atmospheres and exotic compositions (by terrestrial standards), requires a comprehensive treatment of radiative transfer in both. This paper describes work done at Oxford to develop the underlying theory and practical radiative transfer schemes, with particular reference to the NIMS wavelength range, spectral resolution, and scientific objectives for Jupiter. Equivalent work for Venus has already been reported in the literature (e.g. Kamp and Taylor, 1990) and will not be covered in detail here. (C) 1997 COSPAR. Published by Elsevier Science Ltd.