Optimization of organic matter detection using MOMA-like procedures

The early geological history of Mars is comparable to that of Earth, with a probable past presence of liquid water, CHNOPS elements, and energy sources, all of which are essential for a potential emergence of life. The absence of plate tectonics and limited erosion, which expose ancient terrains, make Mars a prime target for the search for traces of life and the study of the habitability of Earth like planets [1].

The Rosalind Franklin rover (ExoMars 2028 mission) will be sent to Mars in 2028. As it is equipped with a drill capable of digging up to 2 meters deep, it will be able to collect and analyze samples relatively protected from the harsh conditions of the surface (particularly radiations and perchlorates). The main objective of this mission is to search for biosignatures such as specific organic compounds (amino acids, carboxylic acids…) using an appropriated instrumental payload [2].

 

In particular, the Mars Organic Molecule Analyzer (MOMA) was designed to separate, detect and identify organic molecules. MOMA has two operational modes based on laser desorption or gas chromatography (GC), both coupled with mass spectrometry (MS) [3].

The organic molecules in the samples collected by the rover must be volatilized before being separated by GC and identified by MS. To do so, the samples can be either pyrolyzed or chemically derivatized. Derivatization agents (MTBSTFA, DMF-DMA, TMAH) are aboard the rover and can be used to increase the volatility of polar molecules while avoiding pyrolysis and potential degradation due to rising temperature.

 

Using a laboratory GC-MS setup, coupled with a pyrolizer, we perform the derivatization-GC-MS analysis of various solid analog samples. This setup reproduces the MOMA hardware constraints as closely as possible, particularly in terms of available time and temperature but also by performing online derivatization with a sample-to-agent ratio similar to that of the MOMA instrument. We studied both natural (from the Arctic, Mauritania…) and artificial samples from a set of samples selected by the ExoMars scientific team in order to test the capacity and complementarity of the rover's payload in detection of organic matter.

After optimizing the analytical sequence, we can detect molecules with strong exobiological potential (such as carboxylic acids, amino acids or nucleobases) in most of the samples.

Although our MOMA-like derivatization-GC-MS setup does not detect as many interesting molecules as other more sensitive laboratory instruments, we aim to explain this difference, determine its performance (limits of detection and quantification) and optimize its analytical parameters.

 

[1] Cockell, Trajectories of Martian Habitability, Astrobiology, 2014, vol 14, num 2

[2] Goesmann et al., The Mars Organic Molecule Analyzer (MOMA) Instrument: Characterization of Organic Material in Martian Sediments, Astrobiology, 2017, vol 17, num 6 & 7

[3] Vago et al., Habitability on Early Mars and the Search for Biosignatures with the ExoMars Rover, Astrobiology, 2017, vol 17, num 6 & 7