Establishing the presence and state of organic matter, including its possible biosignatures, in martian materials has been an elusive quest, despite limited reports of the existence of organic matter ...on Mars. We report the in situ detection of organic matter preserved in lacustrine mudstones at the base of the ~3.5-billion-year-old Murray formation at Pahrump Hills, Gale crater, by the Sample Analysis at Mars instrument suite onboard the Curiosity rover. Diverse pyrolysis products, including thiophenic, aromatic, and aliphatic compounds released at high temperatures (500° to 820°C), were directly detected by evolved gas analysis. Thiophenes were also observed by gas chromatography–mass spectrometry. Their presence suggests that sulfurization aided organic matter preservation. At least 50 nanomoles of organic carbon persists, probably as macromolecules containing 5% carbon as organic sulfur molecules.
Mars methane detection and variability at Gale crater Webster, Christopher R.; Mahaffy, Paul R.; Atreya, Sushil K. ...
Science (American Association for the Advancement of Science),
01/2015, Letnik:
347, Številka:
6220
Journal Article
Recenzirano
Odprti dostop
Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the ...tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.
A single scoop of the Rocknest aeolian deposit was sieved (< 150 µm), and four separate sample portions, each with a mass of ~50 mg, were delivered to individual cups inside the Sample Analysis at ...Mars (SAM) instrument by the Mars Science Laboratory rover's sample acquisition system. The samples were analyzed separately by the SAM pyrolysis evolved gas and gas chromatograph mass spectrometer analysis modes. Several chlorinated hydrocarbons including chloromethane, dichloromethane, trichloromethane, a chloromethylpropene, and chlorobenzene were identified by SAM above background levels with abundances of ~0.01 to 2.3 nmol. The evolution of the chloromethanes observed during pyrolysis is coincident with the increase in O2 released from the Rocknest sample and the decomposition of a product of N‐methyl‐N‐(tert‐butyldimethylsilyl)‐trifluoroacetamide (MTBSTFA), a chemical whose vapors were released from a derivatization cup inside SAM. The best candidate for the oxychlorine compounds in Rocknest is a hydrated calcium perchlorate (Ca(ClO4)2·nH2O), based on the temperature release of O2 that correlates with the release of the chlorinated hydrocarbons measured by SAM, although other chlorine‐bearing phases are being considered. Laboratory analog experiments suggest that the reaction of Martian chlorine from perchlorate decomposition with terrestrial organic carbon from MTBSTFA during pyrolysis can explain the presence of three chloromethanes and a chloromethylpropene detected by SAM. Chlorobenzene may be attributed to reactions of Martian chlorine released during pyrolysis with terrestrial benzene or toluene derived from 2,6‐diphenylphenylene oxide (Tenax) on the SAM hydrocarbon trap. At this time we do not have definitive evidence to support a nonterrestrial carbon source for these chlorinated hydrocarbons, nor do we exclude the possibility that future SAM analyses will reveal the presence of organic compounds native to the Martian regolith.
Key Points
Perchlorates and chlorinated hydrocarbons detected by SAM at Rocknest
Chlorohydrocarbons produced from terrestrial organic carbon and Martian chlorine
No definitive evidence of Martian organic carbon at Rocknest
Earth and Mars, though formed at the same time from the same materials, look very different today. Early in their histories they evolved through some of the same processes, but at some point their ...evolutionary paths diverged, sending them in perhaps irrevocably different directions. Knowledge of the factors that contributed to such different outcomes will help to determine how planets become habitable and how common habitable planets may be. The Mars surface environment is harsh today, but in situ measurements of ancient sedimentary rock by Mars Science Laboratory reveal chemical and mineralogical evidence of past conditions that might have been more favorable for life to exist. But chemistry is only part of what is required to make an environment habitable. Physical conditions constrain the chemical reactions that underlie life processes; the chemical and physical characteristics that make planets habitable are thus entangled.
The Scanning Habitable Environments with Raman and Luminescence for Organics
and Chemicals (SHERLOC) is a robotic arm-mounted instrument on NASA’s Perseverance
rover. SHERLOC has two primary ...boresights. The Spectroscopy boresight generates
spatially resolved chemical maps using fluorescence and Raman spectroscopy coupled to
microscopic images (10.1 μm/pixel). The second boresight is a Wide Angle Topographic
Sensor for Operations and eNgineering (WATSON); a copy of the Mars Science Laboratory
(MSL) Mars Hand Lens Imager (MAHLI) that obtains color images from microscopic
scales (∼13 μm/pixel) to infinity. SHERLOC Spectroscopy focuses a 40 μs pulsed deep UV
neon-copper laser (248.6 nm), to a ∼100 μm spot on a target at a working distance of ∼48
mm. Fluorescence emissions from organics, and Raman scattered photons from organics
and minerals, are spectrally resolved with a single diffractive grating spectrograph with a
spectral range of 250 to ∼370 nm. Because the fluorescence and Raman regions are naturally
separated with deep UV excitation (<250 nm), the Raman region ∼ 800 – 4000 cm−1
(250 to 273 nm) and the fluorescence region (274 to ∼370 nm) are acquired simultaneously
without time gating or additional mechanisms. SHERLOC science begins by using an Autofocus
Context Imager (ACI) to obtain target focus and acquire 10.1 μm/pixel greyscale
images. Chemical maps of organic and mineral signatures are acquired by the orchestration
of an internal scanning mirror that moves the focused laser spot across discrete points on
the target surface where spectra are captured on the spectrometer detector. ACI images and
chemical maps (< 100 μm/mapping pixel) will enable the first Mars in situ view of the spatial
distribution and interaction between organics, minerals, and chemicals important to the
assessment of potential biogenicity (containing CHNOPS). Single robotic arm placement
chemical maps can cover areas up to 7x7 mm in area and, with the < 10 min acquisition
time per map, larger mosaics are possible with arm movements. This microscopic view of
the organic geochemistry of a target at the Perseverance field site, when combined with
the other instruments, such as Mastcam-Z, PIXL, and SuperCam, will enable unprecedented
analysis of geological materials for both scientific research and determination of which samples
to collect and cache for Mars sample return.
The Sample Analysis at Mars (SAM) instrument onboard the Mars Science Laboratory Curiosity rover measures the chemical composition of major atmospheric species (CO2, N2, 40Ar,O2, and CO) through a ...dedicated atmospheric inlet. We report here measurements of volume mixing ratios in Gale Crater using the SAM quadrupole mass spectrometer, obtained over a period of nearly 5 years (3 Mars years) from landing. The observation period spans the northern summer of MY31 and solar longitude (L(sub S)) of 175° through spring of MY 34, L(sub S) = 12°. This work expands upon prior reports of the mixing ratios measured by SAM QMS in the first 105 sols of the mission. The SAM QMS atmospheric measurements were taken periodically, with a cumulative coverage of four or five experiments per season on Mars. Major observations include the seasonal cycle of CO2, N2, and Ar, which lags approximately 20–40° of L(sub S) behind the pressure cycle driven by CO2 condensation and sublimation from the winter poles. This seasonal cycle indicates that transport occurs on faster timescales than mixing. The mixing ratio of O2 shows significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work. The O2 measurements are compared to several parameters, including dust optical depth and trace CH4 measurements by Curiosity. We derive annual mean volume mixing ratios for the atmosphere in Gale Crater: CO2 = 0.951 (±0.003), N2 = 0.0259 (±0.0006), 40Ar = 0.0194 (±0.0004), O2 = 1.61 (±0.09) x 10(exp ‐3), and CO = 5.8 (±0.8) x 10(exp ‐4).
The quadrupole mass spectrometer of the Sample Analysis at Mars (SAM) instrument on Curiosity rover has made the first high‐precision measurement of the nonradiogenic argon isotope ratio in the ...atmosphere of Mars. The resulting value of 36Ar/38Ar = 4.2 ± 0.1 is highly significant for it provides excellent evidence that “Mars” meteorites are indeed of Martian origin, and it points to a significant loss of argon of at least 50% and perhaps as high as 85–95% from the atmosphere of Mars in the past 4 billion years. Taken together with the isotopic fractionations in N, C, H, and O measured by SAM, these results imply a substantial loss of atmosphere from Mars in the posthydrodynamic escape phase.
Key Points
First high‐precision measurement of primordial argon isotopes in Martian air
This measurement definitively ties the“martian” meteorites to Mars”
Requires massive loss of Martian atmosphere after the hydrodynamic escape phase
The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The ...SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL’s Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover’s robotic arm.
The Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) measured a Mars atmospheric14N/15N ratio of 173 ± 11 on sol 341 of the mission, agreeing with Viking's ...measurement of 168 ± 17. The MSL/SAM value was based on Quadrupole Mass Spectrometer measurements of an enriched atmospheric sample, with CO2 and H2O removed. Doubly ionized nitrogen data at m/z 14 and 14.5 had the highest signal/background ratio, with results confirmed by m/z 28 and 29 data. Gases in SNC meteorite glasses have been interpreted as mixtures containing a Martian atmospheric component, based partly on distinctive14N/15N and40Ar/14N ratios. Recent MSL/SAM measurements of the40Ar/14N ratio (0.51 ± 0.01) are incompatible with the Viking ratio (0.35 ± 0.08). The meteorite mixing line is more consistent with the atmospheric composition measured by Viking than by MSL.
Key Points
MSL's more precise results on Mars nitrogen isotopes agree with Viking
Atmospheric gas in Mars meteorites differs from MSL atmospheric composition
Geologically rapid change in atmospheric composition is a possible explanation
The presence and distribution of preserved organic matter on the surface of Mars can provide key information about the Martian carbon cycle and the potential of the planet to host life throughout its ...history. Several types of organic molecules have been previously detected in Martian meteorites1 and at Gale crater, Mars. Evaluating the diversity and detectability of organic matter elsewhere on Mars is important for understanding the extent and diversity of Martian surface processes and the potential availability of carbon sources1,5,6. Here we report the detection of Raman and fluorescence spectra consistent with several species of aromatic organic molecules in the Máaz and Séítah formations within the Crater Floor sequences of Jezero crater, Mars. We report specific fluorescence-mineral associations consistent with many classes of organic molecules occurring in different spatial patterns within these compositionally distinct formations, potentially indicating different fates of carbon across environments. Our findings suggest there may be a diversity of aromatic molecules prevalent on the Martian surface, and these materials persist despite exposure to surface conditions. These potential organic molecules are largely found within minerals linked to aqueous processes, indicating that these processes may have had a key role in organic synthesis, transport or preservation.
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