Design, Development, and Planned Operation of the Mars Organic Molecule Analyzer (MOMA) Investigation on ExoMars
Résumé
The ExoMars 2022 mission brings an enormous opportunity to advance our understanding of possible past or present life on Mars through exploration of a unique environment that may preserve potential molecular biosignatures. With its planned landing site in the ancient, clay-rich Oxia Planum region and its ability to drill to depths of two meters, the Rosalind Franklin rover affords its scientific payload access to materials that may host relatively un-degraded organic compounds from a time when Mars may have had liquid water at its surface and a climate conducive to the development of primitive life forms. Following this opportunity, the rover's payload includes the Mars Organic Molecule Analyzer (MOMA) investigation, which will interrogate acquired drill samples for organic compounds over a wide range of molecular weight, volatility, and structural characteristics. These compounds will be studied both for their intrinsic potential to serve as evidence for biology, and in the context of the broader understanding of organic carbon on Mars provided by other missions (e.g., from the Sample Analysis at Mars, or SAM, investigation on the Curiosity rover) and laboratory studies of martian meteorites and surface material analogs. Through the depth dependence of the concentrations and types of organics, enabled by the sampling drill, MOMA further has the potential to unravel the complex impact of radiation and oxidants on preservation of diagnostic molecular structures over millions or even billions of years. MOMA incorporates multiple analytical protocols into a compact dual ion source mass spectrometer design. Samples delivered to MOMA ovens in the rover's carousel are heated for pyrolysis or derivatization-enhanced evolution into a gas chromatograph (GC) with four available columns to separate a breadth of volatile and semi-volatile analytes including enantiomers of chiral compounds. GC eluent is then analyzed up to molecular weights of 500 Da with a linear ion trap mass spectrometer (ITMS) using electron ionization. Samples delivered to the carousel's refillable container are analyzed with the laser desorption/ionization (LDI) mode of MOMA. LDI directly introduces ionized nonvolatile compounds up to molecular weights of 1000 Da or more into the same ITMS through a fast-acting aperture valve. The structural characteristics of individual compounds can be further investigated by applying a tandem mass spectrometry (MS/MS) protocol during subsequent LDI operations. The combination of GC and LDI analyses is designed to help reveal the full breadth and processing history of organic compounds preserved in Oxia Planum clays. All MOMA flight instrumentation previously installed into the rover has been tested at various levels of system and spacecraft integration and is ready for launch and Mars operations. In parallel the MOMA team is working with a high-fidelity engineering test unit, and numerous laboratory-based analog instruments, to prepare for ExoMars surface science analyses. A MOMA Testbed fully duplicating the flight model, completing development in 2022, will also serve as a clean reference instrument to provide flight mission science and engineering support. This contribution aims at presenting the final configuration of the MOMA experiment prior to the launch of the ExoMars 2022 mission next fall, and to give an overview of its expected analytical performances assessed from key analytical tests performed with the flight model itself, but also with the various laboratory set-ups that will be used to support the treatment and interpretation of the data collected at Mars surface.