Organic cleanliness of the Mars Science Laboratory sample transfer chain

Abstract

One of the primary science goals of the Mars Science Laboratory (MSL) Rover, Curiosity, is the detection of organics in Mars rock and regolith. To achieve this, the Curiosity rover includes a robotic sampling system that acquires rock and regolith samples and delivers it to the Sample Analysis at Mars (SAM) instrument on board the rover. In order to provide confidence that any significant organics detection result was Martian and not terrestrial in origin, a requirement was levied on the flight system (i.e., all sources minus the SAM instrument) to impart no more than 36 parts per billion (ppb by weight) of total reduced carbon terrestrial contamination to any sample transferred to the SAM instrument. This very clean level was achieved by a combination of a rigorous contamination control program on the project, and then using the first collected samples for a "dilution cleaning" campaign of the sample chain prior to delivering a sample to the SAM instrument. Direct cleanliness assays of the sample-contacting and other Flight System surfaces during pre-launch processing were used as inputs to determine the number of dilution cleaning samples needed once on Mars, to enable delivery of suitably clean samples to the SAM experiment. Taking into account contaminant redistribution during launch thorough landing of the MSL on Mars, the amount of residue present on the sampling hardware prior to the time of first dilution cleaning sample acquisition was estimated to be 60 ng/cm(2) on exposed outer surfaces of the sampling hardware and 20 ng/cm(2) on internal sample contacting surfaces; residues consisting mainly of aliphatic hydrocarbons and esters. After three dilution cleaning samples, estimated in-sample contamination level for the first regolith sample delivered to the SAM instrument at the Gale Crater "Rocknest" site was bounded at ≤10 ppb total organic carbon. A Project decision to forego ejecting the dilution cleaning sample and instead transfer the first drill-acquired sample at the "John Klein" site to SAM resulted in an estimated level of terrestrial contamination of ≤430 ppb. The estimated terrestrial contamination for portions from the second drill-acquired sample, at Cumberland, was ≤69 ppb; the estimate for a future, third, drilled sample is ≤38 ppb. These levels are comparable in magnitude to the SAM instrument blanks at the nanomole level (as chlorohydrocarbon).

Solid-Phase Microextraction for Organic Contamination Control Throughout Assembly and Operational Phases of Space Missions

“…Monitoring clean room and hardware organic cleanliness is currently a complex process often involving multiple, expensive, and time-consuming techniques. (National Research Council, 2000;Mahaffy et al, 2003;Blakkolb et al, 2014;Li et al, 2015). Effective monitoring is confounded further by the fact that, in contrast to biological contamination, quantitative limits for organic contamination control are highly specific to the type of mission and are instrument specific.…”

“…Similarly, multi-stepped solvent extraction, followed by pre-concentration of analytes (by evaporation) and analysis by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) techniques were carried out on swabs from surfaces of the MSL sample transfer chain hardware at various stage of construction (Blakkolb et al, 2014). The use of multiple solvents, however, complicated the analysis of the data and diluted the contaminants of interest, reducing sensitivity of the detection.…”

“…Alongside other potential biosignatures such as stable isotopes, atmospheric gases, biosedimentary structures, and macrotextures, organic biomarker compounds are a target for both past habitability and extant life detection efforts (Des Marais et al, 2008). Given the potentially small amounts of organics that may provide a biomarker signal, it is essential to ensure all hardware concerned with sampling is organically clean and free from terrestrial contamination to prevent false positive results (Mahaffy et al, 2003;Blakkolb et al, 2014;Neveu et al, 2018).…”

The International Planetary Protection Handbook

“…Evidence of past or present life can be revealed by the detection of organic compounds that result from biochemical processes. Achieving effective organic compound detection in environments where indigenous organic contents may be very low requires extremely high levels of organic terrestrial contamination/organic cleanliness (Blakkolb et al, 2014). Organic cleanliness has to be maintained during each step in manufacturing, assembly, transport, sample processing and analysis.…”

Planning Considerations Related to the Organic Contamination of Martian Samples and Implications for the Mars 2020 Rover

“…Solvent swab assays (hexane swab sampling, followed by analysis of the swab) prior to shipment of the flight system to the launch site, and then again just prior to last access before fairing encapsulation, showed an average of 23 ng/cm 2 (range, approximately 20-40 ng/cm 2 ) for inner (not exposed) surfaces of the sample transfer chain surfaces. FTIR analysis showed that the contamination was in the form of aliphatic hydrocarbons/ esters (Blakkolb et al, 2014). This contamination was also analyzed by the SAM Science Team at GSFC by ground-based pyrolysis GC-MS, but no organic components were detected (Eigenbrode et al, 2013a).…”