DETECTABILITY OF MOLECULAR-SPECIES IN PLANETARY AND SATELLITE ATMOSPHERES FROM THEIR ROTATIONAL TRANSITIONS

High-resolution spectroscopy in the millimeter and submillimeter range has made significant contributions to the study of chemical compositi on and thermal structure of planetary and satellite atmospheres. This field of research is expected to make considerable progress in the fut ure, from both ground-based and space experiments, with the availabili ty of heterodyne receivers at frequencies up to 1 THz, and with the de velopment of space missions devoted to the exploration of the far-infr ared and submillimeter range. A compilation of guidelines for searchin g molecular species in planetary atmospheres through their rotational transitions, from the millimeter to the fara infrared range (100 mu m) is presented. These transitions are specified, and the corresponding synthetic spectra shown, or detectability limits are estimated. Severa l observational scenarios are considered, (1) ground-based heterodyne observations (such as those with IRAM, CSO, JCMT); (2) space heterodyn e observations with a 3 m antenna (such as that on the European FIRST space mission); (3) Fabry-Perot spectroscopic observations from the gr ound and from space (such as the ISO and FIRST space missions). All pl anets (except Mercury) and the three satellites surrounded by an atmos phere, Titan, Triton and Io, are considered. The main results of this compilation can be summarized as follows. In addition to previously de tected molecules, several species appear as promising candidates for d etection in the far-infrared to millimeter spectral range. For ground- based heterodyne observations, they include : HCl, O-3 and SO on Venus ; HCl, O-3, H2O2 and NO on Mars; HCl in the giant planets; SO on Io. F or space observations, they are: O-2 on Venus and Mars (provided Venus is observable with FIRST), H2O in Saturn and Titan (with ISO and FIRS T); HD, HCl and other halides in the giant planets (ISO). In the case of heterodyne observations, detectability limits are also indicated. T hey typically correspond to mixing ratios in the range 10(-8)-10(-10), depending upon the strength of the observed transition. It should be noted that a 30 m antenna operating at 230 GHz remains very competitiv e, especially for small objects (e.g. Io) with large dilution factors. Heterodyne observations of Triton and Pluto appear beyond the limit o f detection.