SAM Instrument

The Sample Analysis at Mars (SAM) instrument, at NASA's Goddard Space Flight Center, Greenbelt, Md., will analyze samples of material collected by the rover's arm. Credits: NASA-GSFC. Full image and caption ›

The Sample Analysis at Mars (SAM) Suite Investigation in the MSL Analytical Laboratory is designed to address the present and past habitability of Mars by exploring molecular and elemental chemistry relevant to life. SAM addresses carbon chemistry through a search for organic compounds, the chemical state of light elements other than carbon, and isotopic tracers of planetary change.

SAM is a suite of three instruments, a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC), and a Tunable Laser Spectrometer (TLS). The QMS and the GC can operate together in a GCMS mode for separation (GC) and definitive identification (QMS) of organic compounds. The TLS obtains precise isotope ratios for C and O in carbon dioxide and measures trace levels of methane and its carbon isotope.

Three questions about the ability of Mars to support past, present, or future life are addressed by SAM's five science goals as stated in the table below.

SAM Science Goals
Science and Measurement Goal Habitability Question
1) Survery carbon compound sources and evaluate their possible mechanisms of formation and destruction.
2) Search for organic compounds of biotic and prebiotic importance, including methane.
What does the inventory or lack of carbon compounds near the surface of Mars tell us about its potential habitability?
3) Reveal the chemical and isotopic state of elements (i.e. N, H, O, S, and others) that are important for life as we know it.
4) Determine atmospheric composition including trace species that are evidence of interactions between the atmosphere and soil.
What are the chemical and isotopic states of the lighter elements in the solids and in the atmosphere of Mars and what do they tell us about its potential habitability?
5) Better constrain models of atmospheric and climatic evolution through measurements of noble gas and light element isotopes. Were past habitability conditions different from today's?

The three SAM instruments are supported by a sample manipulation system (SMS) and a Chemical Separation and Processing Laboratory (CSPL) that includes high conductance and micro valves, gas manifolds with heaters and temperature monitors, chemical and mechanical pumps, carrier gas reservoirs and regulators, pressure monitors, pyrolysis ovens, and chemical scrubbers and getters. The Mars atmosphere is sampled by CSPL valve and pump manipulations that introduce an appropriate amount of gas through an inlet tube to the SAM instruments. The solid phase materials are sampled by transporting finely sieved materials to one of 74 SMS sample cups that can then be inserted into a SAM oven and thermally processed for release of volatiles. The SAM mechanical configuration and a top level schematic of its sample flow configuration are illustrated below.

SAM Illustration
The illustration of the mechanical configuration of SAM shows the three instruments and several elements of the Chemical Separation and Processing Laboratory.
SAM Flow Diagram
The path of solid and gas samples delivered by MSL subsystems to the SAM instruments is shown. Arrows designate the direction of gas and solid transport.

SAM Instrument Characteristics

Quadrupole Mass Spectrometer
Summary: QMS analyzes the atmosphere, gases thermally evolved from solid phase samples to sub ppb sensitivity. QMS is the primary detector for the GC and can operate in static or dynamic mode.
Mass range 2-535 Dalton (Da)
Detector dynamic range >1010 with pulse counting and Faraday Cup
Crosstalk <106 adjacent unit mass channels (below 150 Da)

Tunable Laser Spectrometer
Summary: Two-channel Herriott cell design spectromenter that provides high sensitivity, unambiguous detection of targeted species (CH4, H2O, and CO2) and selected isotope ratios. One channel is at a wavelength of 3.27 μm for CH4, and the second is at 2.78 μm for CO2 and H2O.
Sensitivity Methane: 2 ppb direct
Water: 2 ppm direct
CSPL enrichment improves by ~100x
Isotopes 13C/12C in methane; 13C/12C in CO2; 18O/16O in CO2; 17O/16O in CO2;
Isotope precision Typically < 10 per mil

Gas Chromatograph
Summary: GC separates complex mixtures of organic compounds into molecular components for QMS and GC stand alone analysis. Helium carrier gase is utilized.
Injection Injection from traps in the SAM manifold or from 3 GC injection traps incorporated into the GC subsystem
6 GC Columns GC1; w/o trap; w/o TCD; MXT20 (C5-C15 organics)
GC2; w/o trap; TCD; MXT5 (> C15 organics)
GC3; trap; TCD; Carbobond (permanent gases)
GC4; trap; TCD; ChirasilDex (chiral compound separation)
GC5; trap; TCD; MXT CLP (C5-C15 organics)
GC6; trap; TCD; MXTQ (C1-C4 organics/N/S compounds)
Detection Limit 10-11 mole

SAM Experiment Sequences

SAM is designed to deliver nine data set types that are acquired via the experiment sequences described in following table. These experiment sequences may utilize different elements of the SAM suite. In addition to these science sequences, the SAM vacuum elements will be cleaned as necessary during the course of the mission by in situ bakeout.

Solid Sample Analysis Sequences
S-PYR Pyrolysis with GCMS (seq. #4) Measurement: Chemical and isotopic analysis of gases evolved from samples as a function of temperature (EGA) and GCMS analysis of organics thermally released from sample.
Experiement Sequence: Quartz cell cleaned in pyrolysis oven; sample delivered to cooled cup; sample heated from ambient to ~1000°C in helium gas stream while evolved gases are monitored by QMS and TLS; GCMS analysis initiated using gases trapped during gas processing in previous step with detection by QMS and GC thermal conductivity detectors.
Notes: 59 quartz cups allow this sequence to be repeated many times over the course of the landed mission. Cups can typically be reused several times.
S-DER Derivatization (seq. #2) Measurement: Analysis of chemically derivatized polar compounds such as amino acids and carboxylic acids that would not otherwise be detected by GCMS.
Experiment Sequence: Foil on metal cup in SMS punctured; sample delivered to one-cup solvent extraction/derivatization cell; sample cup moved to oven for thermal processing; venting of solvent; thermal injection of derivatized compounds onto SAM GC traps; GCMS.
S-CMB Combustion (seq. #8) Measurement: Analysis of carbon isotopes in carbon dioxide produced by combustion in oxygen.
Experiment Sequence: Quartz cell cleaned in pyrolysis oven; sample delivered to cooled cup; sample combusted using oxygen gas; carbon dioxide produced analyzed by TLS for 13C/12C isotopic composition.

Atmospheric Analysis Sequences
A-DIR Direct Atmospheric Measurement (seq. #4) Measurement: QMS and TLS analysis of atmospheric chemical and isotopic composition and seasonal and diurnal variations in trace species abundance.
Experiment Sequence: Atmospheric gas directed into SAM gas manifold; analysis by QMS and TLS scans.
Notes: Duration and number of day time operation may be limited by thermal and energy considerations.
A-ENR Atmospheric Enrichment (seq. #5) Measurement: QMS, TLS, and GCMS analysis of atmospheric trace species.
Experiment Sequence: Atmospheric gas directed over SAM gas traps for enrichment of trace species; gases released from traps and analyzed by GCMS for trace species.
Notes: Direct TLS and QMS measurement also possible during this sequence.
A-MET Methane Enrichment (seq. #6) Measurement: TLS methane analysis with SAM CSPL methane enrichment.
Experiment Sequence: Atmospheric gas directed over SAM gas scrubbers and cold traps; methane released into TLS for isotopic and abundance determination.
Notes: Enrichment sequence may be repeated as necessary for improved methane detection sensitivity.
A-NGE Noble Gas Enrichment (seq. #7) Measurement: Noble gas analysis with SAM CSPL noble enrichment.
Experiment Sequence: Atmospheric gas directed over SAM gas scrubbers and cold traps; noble gases analyzed in SAM QMS operated in static mode.
Notes: Enrichment sequence may be repeated as necessary for improbed noble gas detection sensitivity and precision in isotope measurements.

Calibration Sequences
CAL-GAS In Situ Gas Calibration (seq. #9) Measurement: Calibration gas samples by QMS, TLS, and GCMS to check instrument performance and changes with time.
Experiment Sequence: Gas from SAM calibration gas cell released into manifold; QMS and TLS scans; fluorocarbons trapped on SAM trap; GCMS analysis of fluorocarbons.
Notes: Enrichment sequence repeated on approximately a monthly basis.
CAL-SOL Solid Sample In Situ Calibration (seq. #3) Measurement: Identical to S-PYR sequence, but uses internal calibration standard consisting of carbonate and/or fluorinated carbon compounds.
Experiment Sequence: Metal cup containing sample opened by SMS foil puncture operation; sample heated from ambient to ~850°C in helium gas stream while evolved gases are monitored by QMS and TLS; GCMS analysis initiated to detect fluorocarbons thermally released from cup and trapped during gas processing in previous step; GCMS analysis.
Notes: 6 solid sample calibration cups will be used during the landed mission to check instrument performance.

Last updated: 2012