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Adams D, Luo Y, Wong ML, Dunn P, Christensen M, Dong C, Hu R, Yung Y. Nitrogen Fixation at Early Mars. ASTROBIOLOGY 2021; 21:968-980. [PMID: 34339294 DOI: 10.1089/ast.2020.2273] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The Mars Science Laboratory (MSL) recently discovered nitrates in Gale Crater (e.g., Stern et al., 2015; Sutter et al., 2017). One possible mechanism for ancient nitrate deposition on Mars is through HNOx formation and rain out in the atmosphere, for which lightning-induced NO is likely the fundamental source. This study investigates nitrogen (N2) fixation in early Mars' atmosphere, with implications for early Mars' habitability. We consider a 1 bar atmosphere of background CO2, with abundance of N2, hydrogen, and methane varied from 1% to 10% to explore a swath of potential early Mars climates. We derive lightning-induced thermochemical equilibrium fluxes of NO and HCN by coupling the lightning-rate parametrization from the study of Romps et al. (2014) with chemical equilibrium with applications, and we use a Geant4 simulation platform to estimate the effect of solar energetic particle events. These fluxes are used as input into KINETICS, the Caltech/JPL coupled photochemistry and transport code, which models the chemistry of 50 species linked by 495 reactions to derive rain-out fluxes of HNOx and HCN. We compute equilibrium concentrations of cyanide and nitrate in a putative northern ocean at early Mars, assuming hydrothermal vent circulation and photoreduction act as the dominant loss mechanisms. We find average oceanic concentrations of ∼0.1-2 nM nitrate and ∼0.01-2 mM cyanide. HCN is critical for protein synthesis at concentrations >0.01 M (e.g., Holm and Neubeck, 2009), and our result is astrobiologically significant if secondary local concentration mechanisms occurred. Nitrates may act as high-potential electron acceptors for early metabolisms, although the minimum concentration required is unknown. Our study derives concentrations that will be useful for future laboratory studies to investigate the habitability at early Mars. The aqueous nitrate concentrations correspond to surface nitrate precipitates of ∼1-8 × 10-4 wt % that may have formed after the evaporation of surface waters, and these values roughly agree with recent MSL measurements.
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Affiliation(s)
- Danica Adams
- Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
| | - Yangcheng Luo
- Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
| | - Michael L Wong
- Department of Astronomy and Astrobiology Program, University of Washington, Seattle, Washington, USA
- Virtual Planet Laboratory, University of Washington, Seattle, Washington, USA
| | - Patrick Dunn
- Space Sciences Laboratory, University of California, Berkeley, Berkeley, California, USA
| | - Madeline Christensen
- Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
- Bellarmine Preparatory, Tacoma, Washington, USA
| | - Chuanfei Dong
- Department of Astrophysical Sciences, Princeton University, Princeton, California, USA
| | - Renyu Hu
- Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Yuk Yung
- Department of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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Yeung LY, Li S, Kohl IE, Haslun JA, Ostrom NE, Hu H, Fischer TP, Schauble EA, Young ED. Extreme enrichment in atmospheric 15N 15N. SCIENCE ADVANCES 2017; 3:eaao6741. [PMID: 29159288 PMCID: PMC5693561 DOI: 10.1126/sciadv.aao6741] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 10/26/2017] [Indexed: 06/07/2023]
Abstract
Molecular nitrogen (N2) comprises three-quarters of Earth's atmosphere and significant portions of other planetary atmospheres. We report a 19 per mil (‰) excess of 15N15N in air relative to a random distribution of nitrogen isotopes, an enrichment that is 10 times larger than what isotopic equilibration in the atmosphere allows. Biological experiments show that the main sources and sinks of N2 yield much smaller proportions of 15N15N in N2. Electrical discharge experiments, however, establish 15N15N excesses of up to +23‰. We argue that 15N15N accumulates in the atmosphere because of gas-phase chemistry in the thermosphere (>100 km altitude) on time scales comparable to those of biological cycling. The atmospheric 15N15N excess therefore reflects a planetary-scale balance of biogeochemical and atmospheric nitrogen chemistry, one that may also exist on other planets.
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Affiliation(s)
- Laurence Y. Yeung
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
| | - Shuning Li
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90089, USA
| | - Issaku E. Kohl
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90089, USA
| | - Joshua A. Haslun
- Department of Integrative Biology and Department of Energy Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Nathaniel E. Ostrom
- Department of Integrative Biology and Department of Energy Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA
| | - Huanting Hu
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, USA
| | - Tobias P. Fischer
- Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
| | - Edwin A. Schauble
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90089, USA
| | - Edward D. Young
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA 90089, USA
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Nier AO, McElroy MB. Composition and structure of Mars' Upper atmosphere: Results from the neutral mass spectrometers on Viking 1 and 2. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/js082i028p04341] [Citation(s) in RCA: 412] [Impact Index Per Article: 34.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Masursky H, Boyce JM, Dial AL, Schaber GG, Strobell ME. Classification and time of formation of Martian channels based on Viking data. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/js082i028p04016] [Citation(s) in RCA: 234] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Binder AB, Arvidson RE, Guinness EA, Jones KL, Morris EC, Mutch TA, Pieri DC, Sagan C. The geology of the Viking Lander 1 site. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/js082i028p04439] [Citation(s) in RCA: 140] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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7
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McElroy MB, Kong TY, Yung YL. Photochemistry and evolution of Mars' atmosphere: A Viking perspective. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/js082i028p04379] [Citation(s) in RCA: 224] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Owen T, Biemann K, Rushneck DR, Biller JE, Howarth DW, Lafleur AL. The composition of the atmosphere at the surface of Mars. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/js082i028p04635] [Citation(s) in RCA: 464] [Impact Index Per Article: 38.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Jull AJT, Eastoe CJ, Xue S, Herzog GF. Isotopic composition of carbonates in the SNC meteorites Allan Hills 84001 and Nakhla. ACTA ACUST UNITED AC 2012. [DOI: 10.1111/j.1945-5100.1995.tb01129.x] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Niles PB, Boynton WV, Hoffman JH, Ming DW, Hamara D. Stable Isotope Measurements of Martian Atmospheric CO
2
at the Phoenix Landing Site. Science 2010; 329:1334-7. [PMID: 20829484 DOI: 10.1126/science.1192863] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Paul B. Niles
- Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
| | - William V. Boynton
- Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - John H. Hoffman
- Physics Department, University of Texas, Dallas, TX 75080, USA
| | - Douglas W. Ming
- Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA
| | - Dave Hamara
- Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721, USA
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Abstract
One of the goals of the present Martian exploration is to search for evidence of extinct (or even extant) life. This could be redefined as a search for carbon. The carbon cycle (or, more properly, cycles) on Earth is a complex interaction among three reservoirs: the atmosphere; the hydrosphere; and the lithosphere. Superimposed on this is the biosphere, and its presence influences the fixing and release of carbon in these reservoirs over different time-scales. The overall carbon balance is kept at equilibrium on the surface by a combination of tectonic processes (which bury carbon), volcanism (which releases it) and biology (which mediates it). In contrast to Earth, Mars presently has no active tectonic system; neither does it possess a significant biosphere. However, these observations might not necessarily have held in the past. By looking at how Earth's carbon cycles have changed with time, as both the Earth's tectonic structure and a more sophisticated biology have evolved, and also by constructing a carbon cycle for Mars based on the carbon chemistry of Martian meteorites, we investigate whether or not there is evidence for a Martian biosphere.
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Affiliation(s)
- Monica M Grady
- Planetary and Space Sciences Research Institute, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK.
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Wright IP, Grady MM, Pillinger CT. Stable isotopic measurements of the low-temperature nitrogen components in ALH 84001. ACTA ACUST UNITED AC 1999. [DOI: 10.1029/1998je900023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Grady MM, Wright IP, Pillinger CT. A nitrogen and argon stable isotope study of Allan Hills 84001: implications for the evolution of the Martian atmosphere. METEORITICS & PLANETARY SCIENCE 1998; 33:795-802. [PMID: 11543078 DOI: 10.1111/j.1945-5100.1998.tb01686.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The abundances and isotopic compositions of N and Ar have been measured by stepped combustion of the Allan Hills 84001 (ALH 84001) Martian orthopyroxenite. Material described as shocked is N-poor ([N] approximately 0.34 ppm; delta 15N approximately +23%); although during stepped combustion, 15N-enriched N (delta 15N approximately +143%) is released in a narrow temperature interval between 700 degrees C and 800 degrees C (along with 13C-enriched C (delta 13C approximately +19%) and 40Ar). Cosmogenic species are found to be negligible at this temperature; thus, the isotopically heavy component is identified, in part, as Martian atmospheric gas trapped relatively recently in the history of ALH84001. The N and Ar data show that ALH84001 contains species from the Martian lithosphere, a component interpreted as ancient trapped atmosphere (in addition to the modern atmospheric species), and excess 40Ar from K decay. Deconvolution of radiogenic 40Ar from other Ar components, on the basis of end-member 36Ar/14N and 40Ar/36Ar ratios, has enabled calculation of a K-Ar age for ALH 84001 as 3.5-4.6 Ga, depending on assumed K abundance. If the component believed to be Martian palaeoatmosphere was introduced to ALH 84001 at the time the K-Ar age was set, then the composition of the atmosphere at this time is constrained to: delta 15N > or = +200%, 40Ar/36Ar < or = 3000 and 36Ar/14N > or = 17 x 10(-5). In terms of the petrogenetic history of the meteorite, ALH 84001 crystallised soon after differentiation of the planet, may have been shocked and thermally metamorphosed in an early period of bombardment, and then subjected to a second event. This later process did not reset the K-Ar system but perhaps was responsible for introducing (recent) atmospheric gases into ALH 84001; and it might mark the time at which ALH 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages.
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Affiliation(s)
- M M Grady
- Department of Mineralogy, The Natural History Museum, London, UK.
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Sauke TB, Becker JF. Stable isotope laser spectrometer for exploration of Mars. PLANETARY AND SPACE SCIENCE 1998; 46:805-812. [PMID: 11541820 DOI: 10.1016/s0032-0633(98)00014-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
On Earth, measurements of the ratios of stable carbon isotopes have provided much information about geological and biological processes. For example, fractionation of carbon occurs in biotic processes and the retention of a distinctive 2-4% contrast in 13C/12C between organic carbon and carbonates in rocks as old as 3.8 billion years constitutes some of the firmest evidence for the antiquity of life on the Earth. We have developed a prototype tunable diode Laser spectrometer which demonstrates the feasibility of making accurate in situ isotopic ratio measurements on Mars. This miniaturized instrument, with an optical path length of 10 cm, should be capable of making accurate 13C/12C and 15N/14N measurements. Gas samples for measurement are to be produced by pyrolysis using soil samples as small as 50 mg. Measurements of 13C/12C, 18O/16O and 15N/14N have been made to a precision of better than 0.1% and various other isotopes are feasible. This laser technique, which relies on the extremely narrow emission linewidth of tunable diode lasers (<0.001 cm(-1)) has favorable features in comparison to mass spectrometry, the standard method of accurate isotopic ratio measurement. The miniature instrument could be ready to deploy on the 2003 or other Mars lander missions.
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Affiliation(s)
- T B Sauke
- SETI Institute, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
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17
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Fox JL, Hać A. Spectrum of hot O at the exobases of the terrestrial planets. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97ja02089] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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18
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Fox JL, Hać A. The15N/14N isotope fractionation in dissociative recombination of N2+. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97je00086] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Jull AJT, Eastoe CJ, Cloudt S. Isotopic composition of carbonates in the SNC meteorites, Allan Hills 84001 and Zagami. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/96je03111] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Grady MM, Wright IP, Pillinger CT. A search for nitrates in Martian meteorites. ACTA ACUST UNITED AC 1995. [DOI: 10.1029/94je02803] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
The average tilt of Mars' equator with respect to its orbital plane may have increased significantly over the age of the solar system. Obliquity oscillations might have induced changes in the climate, which altered the mass distribution and hence the solar torque on the planet. Viscous deformation attributable to loading by the large polar caps expected at low obliquity may have induced secular changes in the axial tilt. Earth-like effective viscosities can account for virtually the entire present obliquity of 24.4 degrees. Thus the present average tilt of Mars may not be primordial.
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Wright IP, Grady MM, Pillinger CT. The evolution of atmospheric CO2on Mars: The perspective from carbon isotope measurements. ACTA ACUST UNITED AC 1990. [DOI: 10.1029/jb095ib09p14789] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Fanale FP, Cannon WA. Mars: CO2adsorption and capillary condensation on clays—significance for volatile storage and atmospheric history. ACTA ACUST UNITED AC 1979. [DOI: 10.1029/jb084ib14p08404] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Fanale FP, Cannon WA. Mars: The role of the regolith in determining atmospheric pressure and the atmosphere's response to insolation changes. ACTA ACUST UNITED AC 1978. [DOI: 10.1029/jb083ib05p02321] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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27
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Abstract
Mars, like Earth, may have received its volatiles in the final stages of accretion, as a veneer of volatile-rich material similar to C3V carbonaceous chondrites. The high (40)Ar/(36)Ar ratio and low (36)Ar abundance on Mars, compared to data for other differentiated planets, suggest that Mars is depleted in volatiles relative to Earth-by a factor of 1.7 for K and 14 other moderately volatile elements and by a factor of 35 for (36)Ar and 15 other highly volatile elements. Using these two scaling factors, we have predicted martian abundances of 31 elements from terrestrial abundances. Comparison with the observed (36)Ar abundance suggests that outgassing on Mars has been about four times less complete than on Earth. Various predictions of the model can be checked against observation. The initial abundance of N, prior to escape, was about ten times the present value of 0.62 ppb, in good agreement with an independent estimate based on the observed enhancement in the martian (15)N/(14)N ratio (78,79). The initial water content corresponds to a 9-m layer, close to the value of >/=13 m inferred from the lack of an (18)O/(16)O fractionation (75). The predicted crustal Cl/S ratio of 0.23 agrees exactly with the value measured for martian dust (67); we estimate the thickness of this dust layer to be about 70 m. The predicted surface abundance of carbon, 290 g/cm(2), is 70 times greater than the atmospheric CO(2) value, but the CaCO(3) content inferred for martian dust (67) could account for at least one-quarter of the predicted value. The past atmospheric pressure, prior to formation of carbonates, could have been as high as 140 mbar, and possibly even 500 mbar. Finally, the predicted (129)Xe/(132)Xe ratio of 2.96 agrees fairly well with the observed value of 2.5(+2)(-1) (85). From the limited data available thus far, a curious dichotomy seems to be emerging among differentiated planets in the inner solar system. Two large planets (Earth and Venus) are fairly rich in volatiles, whereas three small planets (Mars, the moon, and the eucrite parent body-presumably the asteroid 4 Vesta) are poorer in volatiles by at least an order of magnitude. None of the obvious mechanisms seems capable of explaining this trend, and so we can only speculate that the same mechanism that stunted the growth of the smaller bodies prevented them from collecting their share of volatiles. But why then did the parent bodies of the chondrites and shergottites fare so much better? One of the driving forces behind the exploration of the solar system has always been the realization that these studies can provide essential clues to the intricate network of puzzles associated with the origin of life and its prevalence in the universe. In our own immediate neighborhood, Mars has always seemed to be the planet most likely to harbor extraterrestrial life, so the environment we have found in the vicinity of the two Viking landers is rather disappointing in this context. But the perspective we have gained through the present investigation suggests that this is not a necessary condition for planets at the distance of Mars from a solar-type central star. In other words, if it turns out that Mars is completely devoid of life, this does not mean that the zones around stars in which habitable planets can exist are much narrower than has been thought (114). Suppose Mars had been a larger planet-the size of Earth or Venus-and therefore had accumulated a thicker veneer and had also developed global tectonic activity on the scale exhibited by Earth. A much larger volatile reservoir would now be available, there would be repeated opportunities for tapping that reservoir, and the increased gravitational field would limit escape from the upper atmosphere. Such a planet could have produced and maintained a much thicker atmosphere, which should have permitted at least an intermittently clement climate to exist. How different would such a planet be from the present Mars? Could a stable, warm climate be maintained? It seems conceivable that an increase in the size of Mars might have compensated for its greater distance from the sun and that the life zone around our star would have been enlarged accordingly.
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Abstract
The two Viking missions to Mars have been extraordinarily successful. Thirteen scientific investigations yielded information about the atmosphere and surface. Two orbiters and landers operating for several months photographed the surface extensively from 1500 kilometers and directly on the surface. Measurements were made of the atmospheric composition, the surface elemental abundance, the atmospheric water vapor, temperature of the surface, and meteorological conditions; direct tests were made for organic material and living organisms. The question of life on Mars remains unanswered. The Viking spacecraft are designed to continue the investigations for at least one Mars year.
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McElroy MB, Kong TY, Yung YL, Nier AO. Composition and Structure of the Martian Upper Atmosphere: Analysis of Results from Viking. Science 1976; 194:1295-8. [PMID: 17797087 DOI: 10.1126/science.194.4271.1295] [Citation(s) in RCA: 59] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Densities for carbon dioxide measured by the upper atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold with average temperatures for both Viking 1 and Viking 2 of less than 200 degrees K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.
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Nier AO, McElroy MB. Structure of the Neutral Upper Atmosphere of Mars: Results from Viking 1 and Viking 2. Science 1976; 194:1298-300. [PMID: 17797088 DOI: 10.1126/science.194.4271.1298] [Citation(s) in RCA: 94] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Neutral mass spectrometers carried on the aeroshells of Viking 1 and Viking 2 indicate that carbon dioxide is the major constituent of the martian atmosphere over the height range 120 to 200 kilometers. The atmosphere contains detectable concentrations of nitrogen, argon, carbon monoxide, molecular oxygen, atomic oxygen, and nitric oxide. The upper atmosphere exhibits a complex and variable thermal structure and is well mixed to heights in excess of 120 kilometers.
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McElroy MB, Yung YL, Nier AO. Isotopic Composition of Nitrogen: Implications for the Past History of Mars' Atmosphere. Science 1976; 194:70-2. [PMID: 17793081 DOI: 10.1126/science.194.4260.70] [Citation(s) in RCA: 146] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in (15)N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N(2) and by dissociative recombination of N(2)(+). The initial partial pressure of N(2) should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO(2) and HNO(3).
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Biemann K, Owen T, Rushneck DR, Lafleur AL, Howarth DW. The Atmosphere of Mars near the Surface: Isotope Ratios and Upper Limits on Noble Gases. Science 1976; 194:76-8. [PMID: 17793083 DOI: 10.1126/science.194.4260.76] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Several new analyses of the martian atmosphere have been carried out with the mass spectrometer in the molecular analysis experiment. The ratios of abundant isotopes of carbon and oxygen are within 10 percent of terrestrial values, whereas nitrogen-15 is considerably enriched on Mars. We have detected argon-38 and set new limits on abundances of krypton and xenon. The limit on krypton is sufficiently low to suggest that the inventories of volatile substances on Mars and on Earth may be distinctly different.
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