Mars, Modulus and MAGIC. The measurement of stable isotopic compositions at a planetary surface

Abstract

Model payloads of any spacecraft destined for the surface of Mars may include an ‘evolved gas analyser’, or EGA. Depending upon one's perception of such a device this may be considered capable of only relatively simple experiments where, for instance, a sample is heated with concomitant detection of the liberated gases. In a sense this approach realises only a limited scientific return. In contrast we contend that an EGA can be part of a very sophisticated instrument which would have the power to reproduce the levels of analytical performance obtained in laboratories on Earth. In this case the apparatus includes, in addition to facilities for heating samples, a gas management system whereby sample gases are separated, purified and quantified, several different gas chromatographic columns optimised for different separation purposes, and a mass spectrometer capable of detecting gases and measuring their stable isotopic compositions. Even using existing materials and technologies the total mass of such a device can be made with a mass of less than 3 kg; a more focused experiment could be performed for < 2 kg. As such it is entirely reasonable to consider that future Mars missions should include such instrumentation, the technical goals of which include measurement of the following isotope ratios: D/H ( 2 H 1 H ), 13 C 12 C , 15 N 14 N , 17 O 16 O , 18 O 16 O , possibly 34 S 32 S and certain key noble gas isotope ratios (for instance Ar and Xe). Scientifically the ambitions of such a project would be to understand the past and present geochemistry of the light elements at the martian surface. Since the elements of interest are implicated in the development of environmental conditions, results would be placed within the context of atmospheric evolution, volatile cycling, surface weathering and martian exobiology.