Detectability of minor constituents in the martian atmosphere by infrared and submillimeter spectroscopy

Spectroscopic remote sensing in the infrared and (sub)millimeter range is a powerful technique that is well suited for detecting minor species in planetary atmospheres (Planet Space Sci. 43(1995) 1485). Yet, only a handful of molecules in the Mars atmosphere ( CO 2 , CO and H 2 O along with their isotopic species, O 3 , and more recently H 2 O 2 and CH 4 ) have been detected so far by this method. New high performance spectroscopic instruments will become available in the future in the infrared and (sub)millimeter range, for observations from the ground (infrared spectrometers on 8 m class telescopes, large millimeter and submillimeter interferometers) and from space, in particular the Planetary Fourier Spectrometer (PFS) aboard Mars Express (MEx), and the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory (HSO). In this paper we will present results of a study that determines detectability of minor species in the atmosphere of Mars, taking into account the expected performance of the above spectroscopic instruments. In the near future, a new determination of the D/H value is expected with the PFS, especially during times of maximum H 2 O abundance in the martian atmosphere. PFS is also expected to place constraints on the abundance of several minor species ( H 2 O 2 , CH 4 , CH 2 O , SO 2 , H 2 S , OCS, HCl) above any local outgassing sources, the hot spots. It will be possible to obtain complementary information on some minor species ( O 3 , H 2 O 2 , CH 4 ) from ground-based infrared spectrometers on large telescopes. In the more distant future, HIFI will be ideally suited for measuring the isotopic ratios with unprecedented accuracy. Moreover, it should be able to observe O 2 , which has not yet been detected spectroscopically in the IR/submm range, as well as H 2 O 2 . HIFI should also provide upper limits for several species that have not yet been detected (HCl, NH 3 , PH 3 ) in the atmosphere of Mars. Some species (SO, SO 2 , H 2 S , OCS, CH 2 O ) that may be observable from the ground could be searched for with present single-dish antennae and arrays, and in the future with the Atacama Large Millimeter Array (ALMA) submillimeter interferometer.