Feasibility of determining the composition of planetary ices by far infrared observations: Application to Martian cloud and surface ices

被引:15
作者
Johnson, BR
Atreya, SK
机构
[1] Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor
基金
美国国家科学基金会; 美国国家航空航天局;
关键词
D O I
10.1006/icar.1996.0027
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Ices in the atmospheres and on the surfaces of planets and moons are thought to play important roles in the evolution and stability of, and in radiative transfer in, planetary atmospheres. In this paper, the capability of far-infrared spectral observations to determine the composition and characteristics of planetary ices is investigated with particular application to martian H2O and CO2 ices. Thin film transmission spectra of crystalline (Ic) and amorphous H2O ice and crystalline CO2 ice were measured using a Fourier transform spectrometer. The far-infrared refractive indices of these ices at temperatures from 77 to 150 K over the spectral range 50 to 500 cm(-1) were derived, These data are in generally good agreement with previously published indices. The refractive index data were incorporated into a radiative transfer model used to study the far-infrared properties of cloud and surface ices on Mars. Typical mid-latitude H2O ice clouds on Mars have vertical far-infrared optical depths on the order of 10(-4), precluding their detection using an earth-based remote sensing instrument, However, model calculations of polar condensates showed observable H2O ice cloud spectral features near the 225 cm(-1) lattice absorption band, The presence of a CO2 ice haze lowered the apparent surface brightness temperature by 10 to 20 K. Theoretical emission by CO2 frost showed strong spectral contrast in the surface brightness temperature of 20 to 30 K near the 66 and 110 cm(-1) lattice bands in solid CO2. In the weakly absorbing inter-band region, CO2 frost emissivity varied from approximately 0.4 to 0.7 with the incorporation of small amounts (0.1-1.0%) of dust or water ice, H2O frost exhibited poor spectral contrast with an emissivity close to unity. The detection of polar hood condensates and of the presence of H2O ice and dust in the CO2 ice caps using an earth-based far-infrared instrument appears feasible, although a telescope with a mirror diameter on the order of 15 to 20 m or interferometric techniques are required to achieve adequate spatial resolution. It is speculated that these and other non-polar ices such as N-2 and CH4, present in the outer solar system, will exhibit far-infrared spectral characteristics similar to CO2 ice, making their detection possible, but technically challenging. (C) 1996 Academic Press, Inc.
引用
收藏
页码:405 / 426
页数:22
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[61]   SPECTRAL ALBEDO AND EMISSIVITY OF CO2 IN MARTIAN POLAR CAPS - MODEL RESULTS [J].
WARREN, SG ;
WISCOMBE, WJ ;
FIRESTONE, JF .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH AND PLANETS, 1990, 95 (B9) :14717-14741