Science

An altitude of 40 km in the terrestrial atmosphere is at the upper end of the ozone layer. This is a region in the atmosphere where there is a lot of photochemistry going on driven by the absorption of solar UV photons. Moreover, there are additional chemical processes because of frequent ion-neutral reactions. Thus, a large variety of complex molecules is expected. Possible in-fall and decomposition of meteorites delivers Si, Mg, Ca, Fe, and other atoms that serve as catalysts for chemical reaction in the middle atmosphere or may be incorporated in chemical compounds. Finally, the formation of large water clusters (and similar large molecules) is expected to be seen. Clearly the chemical composition will be variable with time since, e.g. the solar input is time dependent. Thus, recording a mass spectrum every 65 seconds (about 1 km horizontal scale) will allow to investigate temporal variations and their possible source, given that the platform is almost resting on the pertaining time scales.

Comparison of Earth's and Mars' conditions

The conditions in the Earth stratosphere (polar, 30-40 km altitude) is somewhat similar to the conditions at the Mars surface. That opens up the opportunity to verify instrumentation and equipment for Mars landers under the real (not laboratory) condition of a flight. Tables below provide intercomparison of the physical and chemical (composition) characteristics of the atmospheres of Mars and Earth.

Physical conditions in the Earth stratosphere and Mars surface

Atmospheric composition (%, mixing ratios)

* Earth troposphere. Composition of the Earth atmosphere is approximately the same up to 120 km (= troposphere).

Reference [1] : The planetary scientists companion