SAM (Sample Analysis at Mars) is an experiment which may be proposed for atmospheric, ground and ... more SAM (Sample Analysis at Mars) is an experiment which may be proposed for atmospheric, ground and underground in-situ measurements. One of its main goals is to bring direct or indirect information on the possibility for life to have developed on Mars, and to detect traces of past or present biological activity. A solvent extraction-derivatization method was developed to make refractory molecules analysable (i.e. volatile) and identifiable by GC or/and MS. This method will be completed by pyrolysis and the different gaseous mixtures thus obtained are analysed by GC-MS.
AAS/Division for Planetary Sciences Meeting Abstracts #35, May 1, 2003
ABSTRACT The recent success of the "follow the water" imperative for Mars explo... more ABSTRACT The recent success of the "follow the water" imperative for Mars exploration is tempered by the fact that more than 2 decades after Viking, much remains unknown about the state of carbon at the planet's surface. Therefore, a key objective for lander missions that follow MER will be a search for the location and nature of organic molecules and other carbon containing species. Reduced or partially oxidized compounds may reveal the nature of ancient or even present biotic or prebiotic processes. Ongoing definition and development of advanced techniques and protocols to "follow the carbon" will be described. For example, an instrument suite presently under development to be proposed for inclusion on the 2009 Mars Science Laboratory consists of an advanced gas chromatograph mass spectrometer (GCMS) with derivatization capability coupled with a laser desorption time-of-flight mass spectrometer (LDMS) and a tunable laser spectrometer (TLS). The suite is designated SAM (for Sample Analysis at Mars) and is designed to carry out analysis of both atmospheric gases and volatiles released from solid phase soils, rock samples, and ices. Volatile organic molecules and their pyrolysis products are analyzed by the GCMS and TLS, and refractory organics and elements by the LDMS. Additional objectives include higher precision measurements than have been obtained, to date, of the abundances and isotope ratios of the noble gases and a range of light elements including H, C, O, and N in both the atmosphere and soil. SAM can also contribute to geochemical objectives with the identification of various minerals through evolved gas analysis (EGA) of stable thermal decomposition products such as H2O, CO2, and oxides of nitrogen and sulfur using the MS and TLS as the detector. Recent EGA studies on Mars analogue materials that illustrate this capability are described. This work is supported by funding from NASA and CNES
The Vision and Voyages Planetary Decadal Survey identified a Saturn Probe mission as one of the h... more The Vision and Voyages Planetary Decadal Survey identified a Saturn Probe mission as one of the high priority New Frontiers mission targets[1]. Many aspects of the Saturn system will not have been fully investigated at the end of the Cassini mission, because of limitations in its implementation and science instrumentation. Fundamental measurements of the interior structure and noble gas abundances of Saturn are needed to better constrain models of Solar System formation, as well as to provide an improved context for exoplanet systems. The SPRITE mission will fulfill the scientific goals of the Decadal Survey Saturn probe mission. It will also provide ground truth for quantities constrained by Cassini and conduct new investigations that improve our understanding of Saturn's interior structure and composition, and by proxy, those of extrasolar giant planets.
A Mars surface lander Gas Chromatograph Mass Spectrometer (GCMS) is described to measure the chem... more A Mars surface lander Gas Chromatograph Mass Spectrometer (GCMS) is described to measure the chemical composition of abundant and trace volatile species and isotope ratios for noble gases and other elements. These measurements are relevant to the study of atmospheric evolution and past climatic conditions. A Micromission plan is under study where a surface package including a miniaturized GCMS would be delivered to the surface by a solar heated hot air balloon based system. The balloon system would be deployed about 8 km above the surface of Mars, wherein it would rapidly fill with Martian atmosphere and be heated quickly by the sun. The combined buoyancy and parachuting effects of the solar balloon result in a surface package impact of about 5 m/sec. After delivery of the package to the surface, the balloon would ascend to about 4 km altitude, with imaging and magnetometry data being taken for the remainder of the daylight hours as the balloon is blown with the Martian winds. Total...
Chlorinated compounds highlighted by SAM on Mars could have several origins: from perchlorate and... more Chlorinated compounds highlighted by SAM on Mars could have several origins: from perchlorate and/or MTBSTFA oxidation, from Tenax® degradation with or without presence of perchlorate and/or Martian organics. We have established a list of all the compounds likely to be produced by SAM contamination and compared it with all the compounds detected by SAM.
The Sample Analysis at Mars (SAM) experiment onboard the Curiosity rover detected numerous organi... more The Sample Analysis at Mars (SAM) experiment onboard the Curiosity rover detected numerous organic compounds when analyzing the solid samples collected on the way to Mount Sharp. But MTBSTFA, the chemical reactant for the chemical treatment of the refractory molecules present in the solid samples and present in cups of SAM, was shown to be unfortunately present in the Sample Manipulation System (SMS). During the sample analysis, this chemical species reacts with the organic and inorganic molecules present in the samples. This reaction leads to the production and subsequent detection of numerous MTBSTFA derivatives which makes the treatment and the interpretation of the SAM data complex. Moreover, for the first time on Mars, the wet chemistry method was used on a Cumberland sample to help the GC separation and the MS identification of non volatile compounds. To ensure the identification of the organic molecules and try to discriminate organics generated internally to SAM from those p...
The Sample Analysis at Mars (SAM) instrument on board the Curiosity Rover has detected oxygen and... more The Sample Analysis at Mars (SAM) instrument on board the Curiosity Rover has detected oxygen and HCl gas releases from all analyzed Gale Crater sediments. The presence of perchlorate ClO4(sup-) and/or chlorates ClO3(sup-) are potential sources of the aforementioned O2 releases. The detections of O2 and HCl gas releases and chlorinated hydrocarbons by SAM coupled with the detection of perchlorates by Phoenix Lander's 2008 Wet Chemistry Laboratory all suggest that perchlorates, and possibly chorates, may be present in the Gale Crater sediments. Previous laboratory studies have attempted to replicate these O2 releases by heating perchlorates and chlorates in instruments operated similarly to those in the SAM instrument. Early studies found that pure perchlorates release O2 at temperatures higher than those observed in SAM data. Subsequently, studies were done to test the effects of mixing iron-phase minerals, analogous to those detected on Mars by ChemMin, with perchlorates. The i...
Most of the organics detected on Mars so far are aliphatic and aromatic organo-chlorine compounds... more Most of the organics detected on Mars so far are aliphatic and aromatic organo-chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976; although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO 3 −) and perchlorates (ClO 4 −), along with organic matter present at Mars' surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo-chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families-polycyclic aromatic hydrocarbons, amino acids, and carboxylic acids-in presence of calcium perchlorates. Results show that the polycyclic aromatic hydrocarbon parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the Sample Analysis at Mars instrument could come from the three chemical families studied. Plain Language Summary Organic molecules are the building blocks of life as we know it, and detecting them on the surface of Mars has been one of the major goals of Mars exploration. Viking landers in 1976, followed by the Curiosity rover in 2012, discovered simple chlorine-bearing organics on Mars. These chlorohydrocarbons are known to be mainly produced by the instrument itself, through chemical reactions at high temperatures between other organic molecules thermally extracted from solid rock and soil samples that react with the oxidizing minerals present on Mars (e.g., perchlorates). Studying the influence of the minerals like perchlorates on the thermal extraction of different parent molecules requires thorough experimental studies like this one. Our work constrains the potential parent molecules of the chlorohydrocarbons detected on Mars in the presence of calcium perchlorate, thereby shedding light on the past and present habitability of Mars.
Thermochemolysis of seven nucleobases-adenine, thymine, uracil, cytosine, guanine, xanthine, and ... more Thermochemolysis of seven nucleobases-adenine, thymine, uracil, cytosine, guanine, xanthine, and hypoxanthine-in tetramethylammonium hydroxide (TMAH) was studied individually by pyrolysis gas chromatography mass spectrometry in the frame of the Mars surface exploration. The analyses were performed under conditions relevant to the Sample Analysis at Mars (SAM) instrument of the Mars Curiosity Rover and the Mars Organic Molecule Analyzer (MOMA) instrument of the ExoMars Rover. The thermochemolysis products of each nucleobase were identified and the reaction mechanisms studied. The thermochemolysis temperature was optimized and the limit of detection and quantification of each nucleobase were also investigated. Results indicate that 600°C is the optimal thermochemolysis temperature for all seven nucleobases. The methylated products trimethyl-adenine, 1, 3-dimethyl-thymine, 1, 3-dimethyl-uracil, trimethyl-cytosine, 1, 3, 7-trimethyl-xanthine (caffeine), and dimethyl-hypoxanthine, respectively, are the most stable forms of adenine, thymine, uracil, cytosine, guanine, and xanthine, and hypoxanthine in TMAH solutions. The limits of detection for adenine, thymine, and uracil were 0.075 nmol; the limits of detection for guanine, cytosine, and hypoxanthine were higher, at 0.40, 0.55, and 0.75 nmol, respectively. These experiments allowed to well constrain the analytical capabilities of the thermochemolysis experiments that will be performed on Mars to detect nucleobases.
Dedicated in-situ measurements of Mars' exospheric Ar density by NGIMS/MAVEN highlight profiles d... more Dedicated in-situ measurements of Mars' exospheric Ar density by NGIMS/MAVEN highlight profiles displaying two slopes altitude variation. Below 230 km, the Ar density is characterized by scale height of 13.5 1.7 km and above 400 km by scale height of 156 25 km. A comparison with the model HELIOSARES suggests that the most probable origin of the Ar non-thermal component is the collisional interaction, below the exobase, between the atmospheric Ar and the non-thermal O atoms produced by the dissociative recombination of O2 +. These measurements therefore provide a new approach to constrain one of the main source of Mars' atmospheric escape. They also lead to set up an upper limit on the efficiency of pickup ion sputtering at Mars. The comparison with HELIOSARES suggests that NGIMS detection sensitivity might allow a positive detection of this mechanism if more measurements at high altitude deep in the nightside are performed.
The turbopause and homopause represent the transition from strong turbulence and mixing in the mi... more The turbopause and homopause represent the transition from strong turbulence and mixing in the middle atmosphere to a molecular-diffusion-dominated region in the upper atmosphere. We use neutral densities measured by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmospheric and Volatile EvolutioN spacecraft from February 2015 to October 2016 to investigate the temperature structure and fluctuations of the Martian upper atmosphere. We compare those with temperature measurements of the lower atmosphere from the Mars Reconnaissance Orbiter's Mars Climate Sounder. At the lowest Mars Atmospheric and Volatile EvolutioN altitudes we often observe a statically stable region where waves propagate freely. In contrast, regions from about 20 km up to at least 70 km are reduced in stability where waves are expected to dissipate readily due to breaking/saturation. We derive homopause altitudes from Neutral Gas and Ion Mass Spectrometer N 2 and Ar densities and find that it varies between 60 and 140 km. From the standard deviations in monthly averaged temperature profiles, we determine the wave turbopause altitude where applicable and find that these altitudes agree with the homopause altitudes. We show that the homopause variability is driven by order of magnitude changes in CO 2 densities, which drastically affect the altitude at which the eddy diffusion is equal to the molecular diffusion. These variations are observed as a function of local time, latitude, and season. That the turbopause/homopause does not track a fixed density level means that the eddy diffusion coefficient at the turbopause can vary significantly, suggesting differences in the dominant breaking waves and tidal modes. Plain Language Summary The gases that make up a planet's atmosphere are mixed together efficiently near the surface. But in the uppermost part of the atmosphere, gases separate by mass-heavier ones are held closer to the planet, while lighter ones are more abundant higher up. Because turbulence is responsible for the mixing in the atmosphere, the altitude where this transition occurs is called the turbopause. That turbulence is thought to be generated by atmospheric waves that lose energy (somewhat like ocean waves breaking at shore). In this work, we use measurements of the upper atmosphere from Mars Atmosphere and Volatile Evolution Mission and of the lower atmosphere from Mars Reconnaissance Orbiter to study the turbopause region during a full Mars year. Similar to Earth's atmosphere, we find that below the turbopause wave breaking is strong (which produces turbulence), but above waves can move freely. We also show that the turbopause varies significantly depending on the season and location on the planet. At Mars, gases can escape from the top of the atmosphere, so the relative amounts of escape of different gases depends on the turbopause. Understanding this altitude and why it varies is important for interpreting how the atmosphere evolved.
Journal of Geophysical Research: Space Physics, 2017
During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17-22... more During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17-22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO 2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO 2 densities associated with the longitudinal wave-2 component of nonmigrating tides in the Martian thermosphere. Here we describe the first MAVEN-based study of ionospheric variability using a comprehensive set of solar, atmospheric, and plasma parameters. To do so, we select an altitude where plasma dynamics is not important MENDILLO ET AL. MARS' SOURCES OF IONOSPHERIC VARIABILITY
SAM (Sample Analysis at Mars) is an experiment which may be proposed for atmospheric, ground and ... more SAM (Sample Analysis at Mars) is an experiment which may be proposed for atmospheric, ground and underground in-situ measurements. One of its main goals is to bring direct or indirect information on the possibility for life to have developed on Mars, and to detect traces of past or present biological activity. A solvent extraction-derivatization method was developed to make refractory molecules analysable (i.e. volatile) and identifiable by GC or/and MS. This method will be completed by pyrolysis and the different gaseous mixtures thus obtained are analysed by GC-MS.
AAS/Division for Planetary Sciences Meeting Abstracts #35, May 1, 2003
ABSTRACT The recent success of the "follow the water" imperative for Mars explo... more ABSTRACT The recent success of the "follow the water" imperative for Mars exploration is tempered by the fact that more than 2 decades after Viking, much remains unknown about the state of carbon at the planet's surface. Therefore, a key objective for lander missions that follow MER will be a search for the location and nature of organic molecules and other carbon containing species. Reduced or partially oxidized compounds may reveal the nature of ancient or even present biotic or prebiotic processes. Ongoing definition and development of advanced techniques and protocols to "follow the carbon" will be described. For example, an instrument suite presently under development to be proposed for inclusion on the 2009 Mars Science Laboratory consists of an advanced gas chromatograph mass spectrometer (GCMS) with derivatization capability coupled with a laser desorption time-of-flight mass spectrometer (LDMS) and a tunable laser spectrometer (TLS). The suite is designated SAM (for Sample Analysis at Mars) and is designed to carry out analysis of both atmospheric gases and volatiles released from solid phase soils, rock samples, and ices. Volatile organic molecules and their pyrolysis products are analyzed by the GCMS and TLS, and refractory organics and elements by the LDMS. Additional objectives include higher precision measurements than have been obtained, to date, of the abundances and isotope ratios of the noble gases and a range of light elements including H, C, O, and N in both the atmosphere and soil. SAM can also contribute to geochemical objectives with the identification of various minerals through evolved gas analysis (EGA) of stable thermal decomposition products such as H2O, CO2, and oxides of nitrogen and sulfur using the MS and TLS as the detector. Recent EGA studies on Mars analogue materials that illustrate this capability are described. This work is supported by funding from NASA and CNES
The Vision and Voyages Planetary Decadal Survey identified a Saturn Probe mission as one of the h... more The Vision and Voyages Planetary Decadal Survey identified a Saturn Probe mission as one of the high priority New Frontiers mission targets[1]. Many aspects of the Saturn system will not have been fully investigated at the end of the Cassini mission, because of limitations in its implementation and science instrumentation. Fundamental measurements of the interior structure and noble gas abundances of Saturn are needed to better constrain models of Solar System formation, as well as to provide an improved context for exoplanet systems. The SPRITE mission will fulfill the scientific goals of the Decadal Survey Saturn probe mission. It will also provide ground truth for quantities constrained by Cassini and conduct new investigations that improve our understanding of Saturn's interior structure and composition, and by proxy, those of extrasolar giant planets.
A Mars surface lander Gas Chromatograph Mass Spectrometer (GCMS) is described to measure the chem... more A Mars surface lander Gas Chromatograph Mass Spectrometer (GCMS) is described to measure the chemical composition of abundant and trace volatile species and isotope ratios for noble gases and other elements. These measurements are relevant to the study of atmospheric evolution and past climatic conditions. A Micromission plan is under study where a surface package including a miniaturized GCMS would be delivered to the surface by a solar heated hot air balloon based system. The balloon system would be deployed about 8 km above the surface of Mars, wherein it would rapidly fill with Martian atmosphere and be heated quickly by the sun. The combined buoyancy and parachuting effects of the solar balloon result in a surface package impact of about 5 m/sec. After delivery of the package to the surface, the balloon would ascend to about 4 km altitude, with imaging and magnetometry data being taken for the remainder of the daylight hours as the balloon is blown with the Martian winds. Total...
Chlorinated compounds highlighted by SAM on Mars could have several origins: from perchlorate and... more Chlorinated compounds highlighted by SAM on Mars could have several origins: from perchlorate and/or MTBSTFA oxidation, from Tenax® degradation with or without presence of perchlorate and/or Martian organics. We have established a list of all the compounds likely to be produced by SAM contamination and compared it with all the compounds detected by SAM.
The Sample Analysis at Mars (SAM) experiment onboard the Curiosity rover detected numerous organi... more The Sample Analysis at Mars (SAM) experiment onboard the Curiosity rover detected numerous organic compounds when analyzing the solid samples collected on the way to Mount Sharp. But MTBSTFA, the chemical reactant for the chemical treatment of the refractory molecules present in the solid samples and present in cups of SAM, was shown to be unfortunately present in the Sample Manipulation System (SMS). During the sample analysis, this chemical species reacts with the organic and inorganic molecules present in the samples. This reaction leads to the production and subsequent detection of numerous MTBSTFA derivatives which makes the treatment and the interpretation of the SAM data complex. Moreover, for the first time on Mars, the wet chemistry method was used on a Cumberland sample to help the GC separation and the MS identification of non volatile compounds. To ensure the identification of the organic molecules and try to discriminate organics generated internally to SAM from those p...
The Sample Analysis at Mars (SAM) instrument on board the Curiosity Rover has detected oxygen and... more The Sample Analysis at Mars (SAM) instrument on board the Curiosity Rover has detected oxygen and HCl gas releases from all analyzed Gale Crater sediments. The presence of perchlorate ClO4(sup-) and/or chlorates ClO3(sup-) are potential sources of the aforementioned O2 releases. The detections of O2 and HCl gas releases and chlorinated hydrocarbons by SAM coupled with the detection of perchlorates by Phoenix Lander's 2008 Wet Chemistry Laboratory all suggest that perchlorates, and possibly chorates, may be present in the Gale Crater sediments. Previous laboratory studies have attempted to replicate these O2 releases by heating perchlorates and chlorates in instruments operated similarly to those in the SAM instrument. Early studies found that pure perchlorates release O2 at temperatures higher than those observed in SAM data. Subsequently, studies were done to test the effects of mixing iron-phase minerals, analogous to those detected on Mars by ChemMin, with perchlorates. The i...
Most of the organics detected on Mars so far are aliphatic and aromatic organo-chlorine compounds... more Most of the organics detected on Mars so far are aliphatic and aromatic organo-chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976; although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO 3 −) and perchlorates (ClO 4 −), along with organic matter present at Mars' surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo-chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families-polycyclic aromatic hydrocarbons, amino acids, and carboxylic acids-in presence of calcium perchlorates. Results show that the polycyclic aromatic hydrocarbon parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the Sample Analysis at Mars instrument could come from the three chemical families studied. Plain Language Summary Organic molecules are the building blocks of life as we know it, and detecting them on the surface of Mars has been one of the major goals of Mars exploration. Viking landers in 1976, followed by the Curiosity rover in 2012, discovered simple chlorine-bearing organics on Mars. These chlorohydrocarbons are known to be mainly produced by the instrument itself, through chemical reactions at high temperatures between other organic molecules thermally extracted from solid rock and soil samples that react with the oxidizing minerals present on Mars (e.g., perchlorates). Studying the influence of the minerals like perchlorates on the thermal extraction of different parent molecules requires thorough experimental studies like this one. Our work constrains the potential parent molecules of the chlorohydrocarbons detected on Mars in the presence of calcium perchlorate, thereby shedding light on the past and present habitability of Mars.
Thermochemolysis of seven nucleobases-adenine, thymine, uracil, cytosine, guanine, xanthine, and ... more Thermochemolysis of seven nucleobases-adenine, thymine, uracil, cytosine, guanine, xanthine, and hypoxanthine-in tetramethylammonium hydroxide (TMAH) was studied individually by pyrolysis gas chromatography mass spectrometry in the frame of the Mars surface exploration. The analyses were performed under conditions relevant to the Sample Analysis at Mars (SAM) instrument of the Mars Curiosity Rover and the Mars Organic Molecule Analyzer (MOMA) instrument of the ExoMars Rover. The thermochemolysis products of each nucleobase were identified and the reaction mechanisms studied. The thermochemolysis temperature was optimized and the limit of detection and quantification of each nucleobase were also investigated. Results indicate that 600°C is the optimal thermochemolysis temperature for all seven nucleobases. The methylated products trimethyl-adenine, 1, 3-dimethyl-thymine, 1, 3-dimethyl-uracil, trimethyl-cytosine, 1, 3, 7-trimethyl-xanthine (caffeine), and dimethyl-hypoxanthine, respectively, are the most stable forms of adenine, thymine, uracil, cytosine, guanine, and xanthine, and hypoxanthine in TMAH solutions. The limits of detection for adenine, thymine, and uracil were 0.075 nmol; the limits of detection for guanine, cytosine, and hypoxanthine were higher, at 0.40, 0.55, and 0.75 nmol, respectively. These experiments allowed to well constrain the analytical capabilities of the thermochemolysis experiments that will be performed on Mars to detect nucleobases.
Dedicated in-situ measurements of Mars' exospheric Ar density by NGIMS/MAVEN highlight profiles d... more Dedicated in-situ measurements of Mars' exospheric Ar density by NGIMS/MAVEN highlight profiles displaying two slopes altitude variation. Below 230 km, the Ar density is characterized by scale height of 13.5 1.7 km and above 400 km by scale height of 156 25 km. A comparison with the model HELIOSARES suggests that the most probable origin of the Ar non-thermal component is the collisional interaction, below the exobase, between the atmospheric Ar and the non-thermal O atoms produced by the dissociative recombination of O2 +. These measurements therefore provide a new approach to constrain one of the main source of Mars' atmospheric escape. They also lead to set up an upper limit on the efficiency of pickup ion sputtering at Mars. The comparison with HELIOSARES suggests that NGIMS detection sensitivity might allow a positive detection of this mechanism if more measurements at high altitude deep in the nightside are performed.
The turbopause and homopause represent the transition from strong turbulence and mixing in the mi... more The turbopause and homopause represent the transition from strong turbulence and mixing in the middle atmosphere to a molecular-diffusion-dominated region in the upper atmosphere. We use neutral densities measured by the Neutral Gas and Ion Mass Spectrometer on the Mars Atmospheric and Volatile EvolutioN spacecraft from February 2015 to October 2016 to investigate the temperature structure and fluctuations of the Martian upper atmosphere. We compare those with temperature measurements of the lower atmosphere from the Mars Reconnaissance Orbiter's Mars Climate Sounder. At the lowest Mars Atmospheric and Volatile EvolutioN altitudes we often observe a statically stable region where waves propagate freely. In contrast, regions from about 20 km up to at least 70 km are reduced in stability where waves are expected to dissipate readily due to breaking/saturation. We derive homopause altitudes from Neutral Gas and Ion Mass Spectrometer N 2 and Ar densities and find that it varies between 60 and 140 km. From the standard deviations in monthly averaged temperature profiles, we determine the wave turbopause altitude where applicable and find that these altitudes agree with the homopause altitudes. We show that the homopause variability is driven by order of magnitude changes in CO 2 densities, which drastically affect the altitude at which the eddy diffusion is equal to the molecular diffusion. These variations are observed as a function of local time, latitude, and season. That the turbopause/homopause does not track a fixed density level means that the eddy diffusion coefficient at the turbopause can vary significantly, suggesting differences in the dominant breaking waves and tidal modes. Plain Language Summary The gases that make up a planet's atmosphere are mixed together efficiently near the surface. But in the uppermost part of the atmosphere, gases separate by mass-heavier ones are held closer to the planet, while lighter ones are more abundant higher up. Because turbulence is responsible for the mixing in the atmosphere, the altitude where this transition occurs is called the turbopause. That turbulence is thought to be generated by atmospheric waves that lose energy (somewhat like ocean waves breaking at shore). In this work, we use measurements of the upper atmosphere from Mars Atmosphere and Volatile Evolution Mission and of the lower atmosphere from Mars Reconnaissance Orbiter to study the turbopause region during a full Mars year. Similar to Earth's atmosphere, we find that below the turbopause wave breaking is strong (which produces turbulence), but above waves can move freely. We also show that the turbopause varies significantly depending on the season and location on the planet. At Mars, gases can escape from the top of the atmosphere, so the relative amounts of escape of different gases depends on the turbopause. Understanding this altitude and why it varies is important for interpreting how the atmosphere evolved.
Journal of Geophysical Research: Space Physics, 2017
During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17-22... more During the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission's deep-dip #2 campaign of 17-22 April 2015, spacecraft instruments observed all of the physical parameters needed to assess the photo-chemical-equilibrium (PCE) explanation for ionospheric variability at a fixed altitude (135 km) near the peak of the Martian ionosphere. MAVEN measurements of electron density, electron temperature, neutral CO 2 density, and solar irradiance were collected during 28 orbits. When inserted into the PCE equation, the measurements of varying PCE drivers correlated with the observed electron density variations to within instrumental uncertainty levels. The dominant source of this positive correlation was the variability of CO 2 densities associated with the longitudinal wave-2 component of nonmigrating tides in the Martian thermosphere. Here we describe the first MAVEN-based study of ionospheric variability using a comprehensive set of solar, atmospheric, and plasma parameters. To do so, we select an altitude where plasma dynamics is not important MENDILLO ET AL. MARS' SOURCES OF IONOSPHERIC VARIABILITY
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