Mass spectrometry and planetary exploration: A brief review and future projection

Abstract

Since the inception of mass spectrometry more than a century ago, the field has matured as analytical capabilities have progressed, instrument configurations multiplied, and applications proliferated. Modern systems are able to characterize volatile and nonvolatile sample materials, quantitatively measure abundances of molecular and elemental species with low limits of detection, and determine isotopic compositions with high degrees of precision and accuracy. Consequently, mass spectrometers have a rich history and promising future in planetary exploration. Here, we provide a short review on the development of mass analyzers and supporting subsystems (eg, ionization sources and detector assemblies) that have significant heritage in spaceflight applications, and we introduce a selection of emerging technologies that may enable new and/or augmented mission concepts in the coming decades.

Keywords: Orbitrap; ion trap; mass analyzer; quadrupole; sector field; spaceflight; spectrometry; time-of-flight.

Figure 1

The modularity of key subsystems allows for a number of permutations of mass spectrometer designs, defining unique combinations of hardware capable of targeted applications/chemical measurements

Figure 2

Major milestones in the evolutionary history of mass spectrometry, applied for planetary exploration, show the variety of mass analyzers exploited to date and the progression from instruments offering limited analytical performance to those capable of enhanced science return (expanded mass ranges, higher mass resolving powers, etc). For an even more detailed history than that provided here, the reader is referred to Ren et al16

Figure 3

(A) The mass spectrograph invented by Francis William Aston18 provided the cornerstone by which (B) contemporary double‐focusing sector fields instruments are designed

Figure 4

The analyzer module of the double focusing mass spectrometer (DFMS) instrument, part of the Rosetta Orbiter Sensor for Ion and Neutral Analysis (ROSINA) experiment onboard the Rosetta spacecraft, consists of high‐ and low‐resolution entrance slits, an electrostatic analyzer followed by a magnetic sector, and a suite of “zoom” ion optics that together enable the instrument to achieve a mass resolving power higher than previous sector field mass spectrometer (SFMS) spaceflight instruments. Three distinct detectors support a 10¹⁰ total dynamic range. Image courtesy of the University of Bern

Figure 5

Quadrupole mass filters use an oscillating electric field, including DC and radio frequency (RF) voltages, to permit selected ions with a specific m/z ratio to pass through the rod assembly

Figure 6

Since the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS), more recent quadrupole mass spectrometer (QMS) instruments have implemented longer hyperbolic rods in order to expand mass range and maintain or improve mass resolution. The hyperbolic rods manufactured for the Mars Organic Molecule Analyzer (MOMA) linear ion trap, onboard the ExoMars rover, leverage the same mechanical design as heritage QMS systems. Image modified from Arevalo Jr. et al45

Figure 7

The mass resolving power of a linear time‐of‐flight (TOF) mass analyzer is controlled by variances in the timing, spatial distribution, and kinetic energy spread of ions formed within the source region and transmitted into the analyzer. However, the implementation of an ionization source capable of ultrafast pulsing (eg, femtosecond laser) can attenuate temporal variances in ion formation, and one or more ion mirrors (eg, reflectrons) can normalize the spread in kinetic energies, together improving the achievable mass resolving power of advanced time‐of‐flight mass spectrometer (TOFMS) systems

Figure 8

The COmetary Sampling And Composition (COSAC) instrument deployed on Rosetta's Philae lander was a high‐resolution multipass time‐of‐flight mass spectrometer (TOFMS) that centered on a linear reflectron, with the electron ionization (EI) source (to the right as depicted) and a multi‐sphere‐plate secondary electron multiplier (to the left) on opposite ends, supporting a mass resolving power of m/Δm = 2000 (FWHM). The Engineering Test Unit (ETU) and Flight Model (FM), shown above, conform to the same design with the exception of the electrical harnessing. Image courtesy of Fred Goesmann (principal investigator of COSAC)

Figure 9

Because 2D ion traps focus ions along a line (providing ions one degree of freedom along the z‐axis) while 3D traps compress ions to a single point (no degrees of freedom), 2D traps offer comparatively greater ion storage capacities

Figure 10

The symmetry of the Mars Organic Molecule Analyzer (MOMA) linear ion trap supports two distinct ionization sources (a heritage‐derived electron ionization [EI] source and miniaturized pulsed UV laser) and redundant shielded detector assemblies for mass scanning via radial ion ejection