MOLECULAR SPECTROSCOPY OF PLANETARY ATMOSPHERES

The atmospheres of other planets in the solar system contain a wealth of information regarding their formation and subsequent evolution. Since the outer planets are thought to have evolved little since their formation, the composition of their atmospheres should reflect that of the primordial solar nebula; inner planets, on the other hand, have evolved substantially, and their study provides insight into the evolutionary processes which also affect the earth. Detection and measurement of the constituents of planetary atmospheres therefore provides direct information concerning their present physical states as well as a window into the formation of the entire solar system.

The planetary atmospheres group is currently working on two observational programmes. One is a European satellite experiment called the Long Wavelength Spectrometer, which was launched on the Infrared Space Observatory mission in November 1995; while the other is an ongoing series of ground-based measurements using James Clerk Maxwell Telescope on Mauna Kea, Hawaii. Both of these projects employ incoherent spectroscopic techniques (Fabry-Perot and Michelson, respectively) in the far infrared and submillimetre spectral regions (45 micro.m 1.1 mm) to detect continuum emission and spectral emission lines of atmospheric constituents. This programme of diverse planetary observations, coupled with spectral models based on radiative transfer theory, enables the determination of atmospheric composition with unprecedented accuracy. We have recently shown, for example, that the abundance of hydrogen cyanide in the atmosphere of Jupiter is several orders of magnitude smaller than previously thought, a result which has necessitated a complete reassessment of the chemistry of the Jovian atmosphere.

The methods being developed for ground-based planetary studies also provide a tool for studying the terrestrial atmosphere. If proven to be feasible , a new instrument will be developed at ISAS for this purpose, which can then be used for monitoring atmospheric conditions. In a time of increasing threat to the global environment, this capability to assess anthropogenic affects on atmospheric processes is essential.

Finally, the Canadian satellite experiment Measurements of Pollution in the Troposphere (MOPITT) is scheduled for launch in 1998 and will measure the abundance and distribution of carbon monoxide and methane in the Earth's lower atmosphere. These two gases are important monitors of tropospheric pollution but have never been measured with sufficient accuracy on a global scale over a long time period. We are involved in the laboratory calibration of the flight instrument and in the field validation of the satellite measurements.

The planetary atmospheres group was formed in 1991 and has a number of exciting projects in progress in spite of its relative youth. The group presently consists of one senior scientist and two graduate students. Strong collaborative links have been formed with several research groups elsewhere in Canada and in the USA and England. While all projects are experimental in nature, there is also a need for data analysis and theoretical modelling to complement the development of instrumentation.