The Sample Analysis at Mars (SAM) investigation inside the Curiosity rover is designed to investigate the chemical and isotopic composition of the Martian atmosphere and volatiles extracted from powdered solid surface samples. SAM is capable of conducting highly sensitive search for organic compounds. It can measure the isotopic composition Mars soil or rock that is rich in carbon. Curiosity’s primary science goal is to assess the biological potential of Gale and SAM will support that goal through highly detailed chemical analyses of a limited number of Martian surface and atmospheric samples.
I am writing a ‘limited number’ as any robot can only execute as many sample analyses as we have given it material to react it with. In SAM’s case it means that if we are lucky a maximum of about 300-400 analyses in all can be done. This means that the science team has to choose carefully to spread the capability of analyses over the 98 weeks that Curiosity is meant to roam over Mount Sharp and surroundings. If Curiosity turns out to be as long-lived as Opportunity, we will find ourselves encountering soil samples that we would love to examine with SAM but we will have run out of the capabilities to do so. Such is life for a robot on Mars.
The search for organic molecules is particularly important in the search for life on Mars because life as we know it cannot exist without them (though they can exist without life). SAM will be able to detect lower concentrations of a wider variety of organic molecules than any other instrument yet sent to Mars.
Both the presence and the absence of organic molecules would be important science results, as both would provide important information about the environmental conditions of the region. If SAM does find organic material, the next step would be to determine the origin and the nature of preservation of the molecules. If SAM does not find organic material, a better place to look might be below the surface.
SAM is a suite of three instrumentstotaling 40 kg, located in the Curiosity rover’s interior:
- a Quadrupole Mass Spectrometer (QMS)
- a 6-column Gas Chromatograph (GC),
- a Tunable Laser Spectrometer (TLS).
These instruments are coupled through solid and gas processing systems to provide complementary information on the same samples. Each sample may be analyzed by one, two, or all three of the SAM instruments. [br[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 Carbon (C) and Oxygen (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.
The questions are:
If we find compounds of carbon (or if we don’t), what does that tell us about the habitability of Mars?
- SAM will look into the carbon compound and determine the sources of the carbon compounds.
- SAM will look for organic compounds that (can) derive from living organisms or where living organisms can form from. SAM will try to determine the source of the methane found in the Martian atmosphere.
What do the lighter elements in the soil and atmosphere of Mars tells us about the habitability of Mars?
- SAM will investigate the elements that are important for life as we know it ( i.e. Natrium, Hydrogen, Oxygen and Sulphur)
- SAM will determine the composition of the Martian atmosphere, including any evidence that the soil interacts with the atmosphere.
Were past conditions different from today and what does that mean for the habitability of Mars?
- SAM will measure noble gases, like helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn), and it will also look for light element isotopes
This illustration of the mechanical configuration of SAM shows the three instruments and several elements of the Chemical Separation and Processing Laboratory.
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 hemical Separation and Processing Laboratory (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.
The Gas Chromatograph (GC) has six complementary chromatographic columns. The GC assembly sorts, measures, and identifies gases it separates from mixtures of gases by pushing the mixed gases through long, narrow tubes (wound into coils) with a stream of helium gas. It sorts the gas molecules by weight: they emerge from the tube in order from lightest (out first) to heaviest (out last). Once the gases are sorted, the GC can direct quantities of the separated gases into the QMS or TLS for further analysis.
The Quadrupole Mass Spectrometer (QMS) identifies gases by the molecular weight and electrical charge of their ionized states. It fires high-speed electrons at the molecules, breaking them into fragments. It then sorts the fragments by weight with AC and DC electric fields. The spectra generated by the QMS detector uniquely identify the molecules in the gases.
The Tunable Laser Spectrometer (TLS) uses absorption of light at specific wavelengths to measure concentrations and isotope ratios of specific chemicals important to life: methane, carbon dioxide, and water vapor.
Sieved powdered rock and regolith samples are delivered to small cups in SAM’s Sample Manipulation System (SMS) by Curiosity’s robotic arm through the solid sample inlet tubes. Atmospheric samples are collected through the atmospheric inlets.
The SMS has a wheel of 74 small cups where solid samples are prepared for analysis in one of SAM’s three instruments.
* 59 of the cups are quartz cups are small ovens that can be heated to very high temperatures to pull gases from the powdered samples NOTE; these 59 cups can be reused several times.
* 9 sealed cups are filled with chemical solvents for lower- temperature wet chemistry experiments designed to search for certain polar organic compounds.
* The other 9 cups contain calibration materials.
The chemical separation and processing laboratory includes valves, pumps, carrier-gas reservoirs and regulators, pressure monitors, chemical scrubbers, and two ovens that can heat samples to about 1,000 degrees Celsius (1,800 degrees Fahrenheit). The wide range pump spins at 100,000 revolutions per minute to transfer gas out of the system between analyses of different samples.
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.