point of view of sensitivity, SI RTF would be the facility of choice, providing the 

 capability to observe weak lines (e.g., those of 15 NH 3 and H 2 S). However, the 

 spectral and spatial resolution as presently defined may not be adequate to make 

 the required measurements. ISO will have a similar capability. For the stronger 

 lines, and especially at wavelengths longer than 10 £/m, SOFIA could provide 

 superior spatial and spectral resolution, and in the very near future. For faint 

 sources and high resolution, we will have to wait for LDR. For Jupiter at least, 

 Galileo may obtain the desired information first. 



Measurements of isotope ratios require very high spectral resolution (resolving 

 power, X/AX > 10 4 ), and, if local variations of the ratio are to be determined, 

 high spatial resolution as well (see Appendix C). For H 2 , HD, CH 4 , CH 3 D, and 

 NH 3 , these observations have used the visible and near-infrared regions of the 

 spectrum, but determinations of 13 C/ 12 C and 15 N/ 14 N for Jupiter were made 

 using bands in the infrared. If resolving powers around 10 s can be achieved with 

 sufficient sensitivity, then the instruments aboard HST, SOFIA, SI RTF, and 

 LDR should be able to make useful observations. Resolving power X/AX > 1 3 is 

 not planned for the faint-object spectrograph (FOS) on HST. IUE and then 

 FUSE will be of use if bands of HD (and of C 2 H 2 , etc.) below 3000 A can be 

 detected. For work requiring high spatial resolution (e.g., 0.8 arcsec— about 

 one-tenth the size of the great red spot of Jupiter) we will have to wait for LDR. 



Physical properties of planetary atmospheres can also be determined if accu- 

 rate line shapes can be obtained. High spectral resolution and detector sensitivity 

 are necessary to adequately characterize line profiles and to determine con- 

 tinuum absorption. High spatial resolution is necessary for the study of local 

 conditions. For this work, observations must be made in the infrared or far- 

 infrared regions. Combined data acquired with SOFIA, the SI RTF wide-field 

 camera (WFC) or the LDR medium-resolving-power spectrometer (MRPS) 

 should be useful to meet the proposed resolution and sensitivity requirements at 

 different wavelengths. 



The study of tenuous atmospheres surrounding Pluto and moons in the outer 

 solar system essentially requires high detector sensitivity while maintaining 

 sufficient spectral resolution (X/AX > 10 2 ) to detect molecular absorption or 

 emissions. Spatial resolution is not of great importance provided that individual 

 objects can be isolated. For these studies the HST faint-object spectrograph 

 (FOS) and the LDR MRPS should be useful. 



Since the observations of planetary atmospheres described here primarily 

 involve obtaining and interpreting spectra, laboratory spectra of individual 

 molecules under proper conditions are necessary for comparison. Not only is 

 information about line positions and strengths needed for the determination of 

 the identities and abundances of atmospheric constituents, but the effects of 

 pressure and temperature on spectral line shapes (and positions) need to be mea- 

 sured to determine the atmospheric conditions, hence the locations, where 



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