Mass Spectrometry for Planetary Science

Attaining a satisfactory understanding of the origin and evolution of the solar system and life within it are among the primary scientific goals of current and future planetary missions. One important clue to understanding these questions is the chemical and isotopic composition of atmospheric and surface volatile materials. Sample-return missions may one day become the method of choice for carrying out detailed laboratory studies of these materials. Until then, however, highquality in situ measurements of volatiles will be essential to improving our current knowledge and to providing context and support for future missions. Small (1 kg), high-performance (M/ΔM>10 3 ), space-qualified mass spectrometers are the only known method for quantitative analysis that is capable of delivering the isotopic, atomic, and molecular composition of trace amounts (<10 -13 moles/gram) of sample materials. Of particular interest is the identification of biomarker molecules to roughly that level on Mars. These are very difficult performance goals in their own right, but they are more so when increasingly constrained mission resources are taken into account. The current state-of-the-art in space-borne mass spectrometry is examined by defining a quality metric proportional to (performance/resources). The metric suggests that future requirements and constraints represent significant technical challenges. This paper briefly examines historical progress in planetary mass spectrometry before moving to the principles of particle optics that govern spectrometer design and implementation. Several alternative methods are examined, but only four are examined in detail: quadrupole, ion trap, magnetic, and time-of-flight spectrometry. This choice reflects both past successes and the promise of the methodology for future adaptations.