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At least 163 records · Page 9

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NASA NTRS2007

Astrobiological Significance of Microbial Extremophiles

The microflora of the cryosphere of planet Earth provides the best analogs for life forms that might be found in the permafrost or polar ice caps of Mars, near the surface of the cometary nuclei, or in the liquid water beneath and the ice crusts of icy moons of Jupiter and Saturn. The importance of study alkaliphilic microorganisms for astrobiology was enhanced by the findings of abundant carbonates and carbonate globules rimmed with possibly biogenic magnetites in association with the putative microfossils in the ALH84001 meteorite. Although the ALH84001 "nanofossils" were to small and simple to be unambiguously recognized as biogenic, they stimulated Astrobiology research and studies of microbial extremophiles and biomarkers in ancient rocks and meteorites. Recent studies of CI and CM carbonaceous meteorites have resulted in the detection of the well-preserved mineralized remains of coccoidal and filamentous microorganisms in cyanobacterial mats. Energy Dispersive X-ray Analysis has shown anomalous biogenic element ratios clearly indicating they are not recent biological contaminants. This paper reviews microbial extremophiles in context of their significance to Astrobiology. The study of halophilic microorganisms was started from work with saline soils and lakes, and one of the record of good growth for Haloferax mediterranei was shown at 30 percent NaC1. Although alkali-tolerant nitrifying bacteria had previously been reported, the first described alkaliphilic microorganism was the bacterium Streptococcus faecalis. Halophilic and alkaliphilic forms are relevant to conditions that might be found in closed impact basins and craters on Mars filled with evaporite deposits. The first obligately acidophilic bacterium described was Acidithiobacillus ferrooxydans (formally Thiobacillus ferrooxidans). Later thermophilic lithotrophic acidophiles were found, and the hyperacidophilic moderately thermophilic species of the genus Picrophilus were found to grow at negative pH. The epoch of study of thermophilic microorganisms starts with the discovery of Thermus aquaticus, and presently the maximum temperature for growth at 113 C was found for Pyrolobus fumarii. The microorganisms capable of growth at high temperatures and in hyperacidic environments on Earth are good analogs for life that might be able to survive in hot acidic droplets in the upper regimes of the atmosphere of Venus. The study of barophiles was made possible by engineering achievements leading to the development of the submersible crafts used to study the Black Smokers of the Deep-sea Hydrothermal vents. The first described radioresistant bacterium Deinococcus radiodurans can survive ionizing irradiation and other DNA-damaging assaults at doses that are lethal to all other organisms. These microbes are models for life that might endure high radiation environments in the ice near the surface of comets or on the icy moons of Jupiter and Saturn and in the seafloor deep beneath icy crusts Europa and Enceladus. This paper presents ESEM and FESEM images showing intact microbes preserved in the deep ice cores extracted from just above Lake Vostok, Antarctica that are considered analogs for life forms that might survive on comets and icy moons.

Pikuta, Elena V.↗

NASA NTRSDate not supplied

TPSAS-NF1676L-13393-DND

In the two plus decades since it became evident that polar stratospheric clouds (PSCs) play a major role in the springtime depletion of polar ozone, the detailed composition and morphology of PSCs has been an area of interest. Although our PSC knowledge base is substantial, there is still considerable uncertainty in specific key areas related to their composition and formation. Probably the least well understood of these is the nucleation process responsible for the formation of nitric acid trihydrate (NAT) particles and the circumstances under which NAT formation and growth leads to stratospheric denitrification. CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) is an excellent instrument for observing PSCs and has already produced an extensive set of PSC observations with unprecedented spatial and temporal resolution covering five winters. These observations are providing new insight into the key remaining questions regarding PSC composition and formation mechanisms. In this paper, we examine the CALIOP PSC observations in combination with a microphysical model in attempt to better understand the underlying physical mechanisms for NAT nucleation. Of particular interest is the early phase of the 2009-2010 Arctic winter when CALIOP frequently observed extended regions of tenuous NAT clouds, clearly before ice was present in the polar vortex. This provides unprecedented large-scale evidence that ice particles are not the only nuclei on which NAT may form. Microphysical model calculations along backward trajectories from these CALIOP NAT cloud observations are used to investigate possible ice-independent, heterogeneous NAT nucleation mechanisms. These analyses will then be expanded to other winters to assess the overall significance of an ice-independent nucleation mechanism for NAT PSCs.

M C Pitts↗

DOE OSTI2024

SAIL Supermicron Bioaerosol (SSB) Field Campaign Report

The Surface Atmosphere Integrated Field Laboratory (SAIL) Supermicron Bioaerosol (SSB) study was designed to complement the larger Atmospheric Radiation Measurement (ARM) SAIL science goals to understand aerosol processes and aerosol-cloud interactions in the Colorado River’s East River Watershed Basin. Supermicron aerosol, particles larger than one micron in diameter, and bioaerosols, primary particles containing biological material, are important for understanding atmospheric processes and sources within high mountainous terrain. For example, they can interact with clouds and the water cycle such as by serving as nuclei for cloud droplets and ice crystals that can eventually result in precipitation events. These particles can also be recycled back to the surface via wet and dry deposition, where they can alter plant and microbial growth and/or be reemitted again, forming a positive feedback loop within the Earth system known as bioprecipitation.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2025

Elucidating Processes Controlling Arctic Atmospheric Aerosol Sources, Aging, and Mixing States (Final Report)

Atmospheric aerosols play critical roles in the Earth’s energy budget, directly by scattering or absorbing solar and terrestrial radiation and indirectly by serving as seeds (nuclei) for cloud droplet and ice crystal formation and by depositing on snow and ice surface, thereby changing the surface albedo. These effects are dependent on aerosol particle size and chemical composition and impact the hydrological cycle as well. This project provided single-particle size and chemical composition measurements across the entire annual cycle in the high Arctic and in the Alaskan Arctic during fall – winter, addressing the most significant gaps in Arctic aerosol observational data. These needs were based on recent rapid sea ice loss across the entire Arctic, as well as the major annual delays in sea ice freeze-up during fall in the Chukchi Sea and increased wintertime sea ice fracturing in the Beaufort Sea, both off the North Slope of Alaska. Two DOE Atmospheric Radiation Measurement (ARM) field campaigns were conducted for atmospheric aerosol sampling. The Aerosols during the Polar Utqiagvik Night (APUN – ‘snow on ground’ in Iñupiaq) ARM field campaign at Utqagivik, Alaska was conducted from Oct. 28 – Dec. 22, 2018. Aerosol sizing instrumentation and a single-particle mass spectrometer were successfully deployed for size-resolved number concentration measurements and measurements of individual particle size and chemical composition, respectively. These results show the influence of locally-produced sea spray aerosol, with high cloud-forming potential, due to delayed sea ice freeze-up in the fall. During the 2019‐2020 international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, daily atmospheric aerosol particles were collected aboard the German icebreaker Polarstern in the Central Arctic from Nov. 2019 – Oct. 2020. Sea salt aerosol and marine organics were observed year-round during MOSAiC with varying morphologies and sources. These findings are important because most Arctic models do not include a sea spray aerosol source, despite this source increasing with declining sea ice extent. In addition to collecting new samples and data, this project also conducted further analysis of previously collected single-particle chemical composition measurements within the North Slope of Alaska oil fields and at Utqiaġvik, AK, during Aug. – Sep. 2015 and 2016 field campaigns. This work resulted in the discovery of chemical reactions of oil field combustion emissions occurring within fog droplets across the North Slope of Alaska and forming secondary aerosol, showing the impact of Arctic oil field emissions beyond black carbon aerosol and greenhouse gases. In addition, the distribution of chemical species across the aerosol population within the oil fields was quantified, using these data and a previously development framework. We also presented the first ambient evidence of the collision of two atmospheric particles resulting in formation of an organic-coated ammonium sulfate particle of marine origin, which has implications for cloud formation with declining sea ice extent. Overall, this project has elucidated connections between seawater biogeochemistry, resource extraction activities, atmospheric composition, clouds, and the energy budget of the Arctic region. The results of this project are expected to improve weather and sea ice forecasting for security and development in the Arctic and beyond.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1974

Cometary coma ions

For comets whose nuclei are composed of water ice conglomerates it is shown that the ion H3O(+) can predominate to distances of 5000 km in the subsolar direction. Beyond this distance H2O(+) is the most important ion. The crossover point is a sensitive function of the rate of evaporation from the nucleus. The presence of ammonia or metals such as sodium, in concentrations greater than 0.1% H2O, can lead to NH4(+) and Na(+) ions.

Aikin, A. C.↗

NASA NTRS1974

Cometary coma ions

Aikin, A. C.↗

NASA NTRS1976

Neutral temperature of cometary atmospheres

Spectral analyses of the coma and type I tails of a comet indicate that the main constituent of a cometary atmosphere is H2O and that cometary nuclei are composed of dirty ice containing mainly CO and N2. Thermochemical calculations on strong infrared coupling between H2O and dust grains explain the dependence of atmospheric temperature on the distance of the comet from the sun considering the strong cooling effect of H2O. It is concluded that atmospheric temperatures of comets cannot be so high as 1500 K.

Shimizu, M.↗

NASA NTRS1986

A fractal model of a cometary nucleus formed by random accretion

Numerical simulations of the structure of aggregates of grains in the solar system show they are fractals with low density and irregular shapes. Comet nuclei forming from a mixture of ice and dust grains are likely to have nonuniform composition as well as structure. Such a nucleus appears to account for observed characteristic of comets. The structure has significant implications for the evolution of cometary nuclei.

Donn, Bertram↗

NASA NTRS1981

Thermal modeling of cometary nuclei

A model of the sublimation of volatile ices from a cometary nucleus is presented which includes the effects of (1) diurnal heating and cooling, (2) rotation period and pole orientation, (3) the thermal properties of the ice and subsurface layers, and (4) the contributions from coma opacity, scattering and thermal emission where the properties of the coma are derived from the integrated rate of volatile production by the nucleus. In applying the model to the case of the 1986 apparition of Halley's comet, it is found that the generation of a cometary dust coma increases the total energy reaching the Halley nucleus due to the greater geometrical cross-section of the coma as compared with the bare nucleus. The calculated coma opacity of Halley is about 0.2 at 1 AU from the sun and 1.2 at perihelion. Possible consequences of the results obtained for the generation of nongravitational forces, volatile production rates for comets and cometary lifetimes against sublimation are discussed.

Weissman, P. R.↗

NASA NTRS2012

The Mars Dust Cycle: Investigating the Effects of Radiatively Active Water Ice Clouds on Surface Stresses and Dust Lifting Potential with the NASA Ames Mars General Circulation Model

The dust cycle is a critically important component of Mars' current climate system. Dust is present in the atmosphere of Mars year-round but the dust loading varies with season in a generally repeatable manner. Dust has a significant influence on the thermal structure of the atmosphere and thus greatly affects atmospheric circulation. The dust cycle is the most difficult of the three climate cycles (CO2, water, and dust) to model realistically with general circulation models. Until recently, numerical modeling investigations of the dust cycle have typically not included the effects of couplings to the water cycle through cloud formation. In the Martian atmosphere, dust particles likely provide the seed nuclei for heterogeneous nucleation of water ice clouds. As ice coats atmospheric dust grains, the newly formed cloud particles exhibit different physical and radiative characteristics. Thus, the coupling between the dust and water cycles likely affects the distributions of dust, water vapor and water ice, and thus atmospheric heating and cooling and the resulting circulations. We use the NASA Ames Mars GCM to investigate the effects of radiatively active water ice clouds on surface stress and the potential for dust lifting. The model includes a state-of-the-art water ice cloud microphysics package and a radiative transfer scheme that accounts for the radiative effects of CO2 gas, dust, and water ice clouds. We focus on simulations that are radiatively forced by a prescribed dust map, and we compare simulations that do and do not include radiatively active clouds. Preliminary results suggest that the magnitude and spatial patterns of surface stress (and thus dust lifting potential) are substantial influenced by the radiative effects of water ice clouds.

Kahre, Melinda A.↗

NASA NTRS1989

What if chondritic porous interplanetary dust particles are not the real McCoy

To select a target comet for a Comet Nucleus Sample Return Mission (CNSRM) it is necessary to have an experimental data base to evaluate the extent of diversity and similarity of comets. For example, the physical properties (e.g., low density) of chondritic porous (CP) interplanetary dust particles (IDPs) are believed to resemble these properties of cometary dust although it is yet to be demonstrated that the porous structure of CP IDPs is inherent to presolar dust particles stored in comet nuclei. Porous structures of IDPs could conceivably form during sublimation at the surface of active comet nuclei. Porous structures are also obtained during annealing of amorphous Mg-SiO smokes which initially forms porous aggregates of olivine + platey tridymite and which, upon continued annealing, react to fluffy enstatite aggregates. It is therefore uncertain that CP IDPs are entirely composed of unmetamorphosed presolar dust. Conceivably, new minerals and textures may form in situ in nuclei of active comets as a function of their individual thermal history. Unmetamorphosed comet dust is probably structurally amorphous. Thermal annealing of this dust can produce ultra fine-grained minerals and this ultrafine grain size of CP IDPs should be considered in assessments of aqueous alterations that could affect presolar dust in comet nuclei between 200 and 400 K. Devitrification and hydration may occur in situ in ice-dust mixtures and the mantle of active comet nuclei. Devitrification, or uncontrolled crystallization, of amorphous precursor dust can produce a range of chemical compositions of ultrafine-grained minerals and (non-equilibrium) mineral assemblages and textures in dust contained in comet nuclei as a function of period and trajectory of orbit and number of perihelion passages (not considering internal heating). Thus, experimental data on relevant processes and reaction rates between 200 and 400 K are needed in order to evaluate comet selection, penetration depth for sampling device and curation of samples for CNSRM.

Rietmeijer, Frans J. M.↗

NASA NTRS1991

Outer planets and icy satellites

The resources offered by the outer bodies in the Solar System, starting with the main belt asteroids and Jovian System, are not only larger and more diverse but may even be easier to reach than, say, those of Mars. The use of their material, including water and organic matter, depends exclusively on the general strategy of exploration of the Solar System. Of major interest in this respect are the large ice satellites - Titan, Ganymede, and Callisto. Motion through the planetary magnetospheres excites in their ice envelopes megampere currents which, in the presence of rocky, etc., inclusions with electronic conduction should lead to the bulk electrolysis of ice and accumulation in it of 2H2 + O2 in the form of a solid solution. With the concentration of 2H2 + O2 reaching about 15 wt. percent, the solution becomes capable of detonation by a strong meteoritic impact. An explosion of Ganymede's ice envelope about 0.5 By ago could account for the formation of the Trojans and irregular satellites, all known differences between Ganymede and Callisto, and many other things. The explosion of a small icy planet with M approx less than 0.5 Moon created the asteroid belt. Two to three explosions occurred on Io, and two on Europa. The specific features of the longperiod comets close to Saturn's orbit permit dating Titan's envelope explosion as 10,000 yr ago, which produced its thick atmosphere, young Saturn's rings, as well as a reservoir of ice fragments saturated by 2H2 + O2, i.e., cometary nuclei between the orbits of Jupiter and Saturn. Thus these nuclei should contain, besides organic matter, also 2H2 + O2, which could be used for their transportation as well as for fuel for spaceships. Ices of such composition can reside deep inside Deimos, the Trojans, C-asteroids, etc. The danger of a future explosion of Callisto's electrolyzed ices, which would result in a catastrophic bombardment of the Earth by comets, may be high enough to warrant a revision of the priorities and strategy of space exploration.

Drobyshevski, E. M.↗

DOE OSTI2022

Equal abundance of summertime natural and wintertime anthropogenic Arctic organic aerosols

Aerosols play an important yet uncertain role in modulating the radiation balance of the sensitive Arctic atmosphere. Organic aerosol is one of the most abundant, yet least understood, fractions of the Arctic aerosol mass. Here we use data from eight observatories that represent the entire Arctic to reveal the annual cycles in anthropogenic and biogenic sources of organic aerosol. We show that during winter, the organic aerosol in the Arctic is dominated by anthropogenic emissions, mainly from Eurasia, which consist of both direct combustion emissions and long-range transported, aged pollution. In summer, the decreasing anthropogenic pollution is replaced by natural emissions. These include marine secondary, biogenic secondary and primary biological emissions, which have the potential to be important to Arctic climate by modifying the cloud condensation nuclei properties and acting as ice-nucleating particles. Their source strength or atmospheric processing is sensitive to nutrient availability, solar radiation, temperature and snow cover. Our results provide a comprehensive understanding of the current pan-Arctic organic aerosol, which can be used to support modelling efforts that aim to quantify the climate impacts of emissions in this sensitive region.

58 GEOSCIENCES↗

NASA NTRS1978

On the nature and origin of comets and their contribution to planets

The rotation of cometary nuclei and certain properties of cometary ices are discussed. Observations show that comets were formed at extremely low temperatures and probably contain amorphous ices that give off exothermal energy on mild heating. While a large comet has a slow rotation period, many smaller typical comets appear to be rotating rapidly, indicating that encounters among them were frequent during formation. An estimate for the product of the relaxation time for encounters and the mean space density near the end of comet formation is presented, and a time scale of approximately 1,000,000 yr for comet accumulation is suggested. Some probable and possible contribution of comets to the solar system are summarized.

Whipple, F. L.↗

NASA NTRS2010

A Comparison of Oxidized Carbon Abundances among Comets

Comets contain relatively well preserved icy material remaining from the epoch of Solar System formation, however the extent to which these ices are modified from their initial state remains a fundamental question in cometary science. As a comet approaches the Sun, sublimation of the ices contained in its nucleus (termed " native ices") releases parent volatiles into the coma, where they can be measured spectroscopically. One means of assessing the degree to which interstellar ices were processed prior to their incorporation into cometary nuclei is to measure the relative abundances of chemically-related parent volatiles. For example, formation of C2H6 by hydrogen atom addition (e.g., to C2H2) on surfaces of ice-mantled grains was proposed to explain the high C2H6 to CH4 abundance observed in C/1996 B2 (Hyakutake) [1]. The large C2H6/CH4 abundance ratios measured universally in comets, compared with those predicted by gas phase production of C2H6, establishes H-atom addition as an important and likely ubiquitous process. CO should also be hydrogenated on grain surfaces. Laboratory irradiation experiments on interstellar ice analogs indicate this to require very low temperatures (T approx. 10-25 K), the resulting yields of H2CO and CH3OH being highly dependent both on hydrogen density (i.e., fluence) and on temperature ([2],[3]). This relatively narrow range in temperature reflects a lack of mobility below 8-10 K on the one hand, and reduced sticking times for H-atoms as grain surfaces are warmed above 20 K on the other. The relative abundances of these three chemically-related molecules in comets provides one measure of the efficiency of H-atom addition to CO on pre-cometary grains (Fig. 1).

DiSanti, M. A.↗

NASA NTRS1998

Modeling Macro- and Micro-Scale Turbulent Mixing and Chemistry in Engine Exhaust Plumes

Simulation of turbulent mixing and chemical processes in the near-field plume and plume-vortex regimes has been successfully carried out recently using a reduced gas phase kinetics mechanism which substantially decreased the computational cost. A detailed mechanism including gas phase HOx, NOx, and SOx chemistry between the aircraft exhaust and the ambient air in near-field aircraft plumes is compiled. A reduced mechanism capturing the major chemical pathways is developed. Predictions by the reduced mechanism are found to be in good agreement with those by the detailed mechanism. With the reduced chemistry, the computer CPU time is saved by a factor of more than 3.5 for the near-field plume modeling. Distributions of major chemical species are obtained and analyzed. The computed sensitivities of major species with respect to reaction step are deduced for identification of the dominant gas phase kinetic reaction pathways in the jet plume. Both the near field plume and the plume-vortex regimes were investigated using advanced mixing models. In the near field, a stand-alone mixing model was used to investigate the impact of turbulent mixing on the micro- and macro-scale mixing processes using a reduced reaction kinetics model. The plume-vortex regime was simulated using a large-eddy simulation model. Vortex plume behind Boeing 737 and 747 aircraft was simulated along with relevant kinetics. Many features of the computed flow field show reasonable agreement with data. The entrainment of the engine plumes into the wing tip vortices and also the partial detrainment of the plume were numerically captured. The impact of fluid mechanics on the chemical processes was also studied. Results show that there are significant differences between spatial and temporal simulations especially in the predicted SO3 concentrations. This has important implications for the prediction of sulfuric acid aerosols in the wake and may partly explain the discrepancy between past numerical studies (that employed parabolic or temporal approximations) and the measured data. Finally to address the major uncertainty in the near-field plume modeling related to the plume processing of sulfur compounds and advanced model was developed to evaluate its impact on the chemical processes in the near wake. A comprehensive aerosol model is developed and it is coupled with chemical kinetics and the axisymmetric turbulent jet flow models. The integrated model is used to simulate microphysical processes in the near-field jet plume, including sulfuric acid and water binary homogeneous nucleation, coagulation, non-equilibrium heteromolecular condensation, and sulfur-induced soot activation. The formation and evolution of aerosols are computed and analyzed. The computed results show that a large number of ultra-fine (0.3--0.6 nm in radius) volatile HSO4 - HO embryos are generated in the near-field plume. These embryos further grow in size by self coagulation and condensation. Soot particles can be activated by both heterogeneous nucleation and scavenging of H2SO4-H2O aerosols. These activated soot particles can serve as water condensation nuclei for contrail formation. Conditions under which ice contrails can form behind aircrafts are studied. The sensitivities of the threshold temperature for contrail formation with respect to aircraft propulsion efficiency, relative humidity, and ambient pressure are evaluated. The computed aerosol properties for different extent of fuel sulfur conversion to S(VI) (SO3 and H2SO4) in engine are examined and the results are found to be sensitive to this conversion fraction.

Menon, Suresh↗

NASA NTRS1995

Comets, impacts, and atmospheres

We are proposing a model for the delivery of volatiles to the inner planets by icy planetesimals (comets). Laboratory studies of the trapping of gases in ice forming at low temperatures simulate the formation of comet nuclei at various distances from the Sun in the solar nebula. The total gas content as well as the relative proportions of gases trapped in the ice are strong functions of temperature. As they trap N2 inefficiently, all planetesimals formed interior to Neptune are deficient in nitrogen, acquiring values of C/N resembling those found in the inner planet volatile inventories. A mixture of three basic types of comets appears capable of accounting for the observed volatile inventories on Venus, Earth, and Mars, with the caveat that impact erosion is necessary to explain the present condition of the martian atmosphere. The model includes the possibility of several epochs of clement conditions on early Mars. Some tests of these ideas are suggested, including measurements in Jupiter's atmosphere by the Galileo probe.

Non-NASA Center↗

NASA NTRS1991

Water/rock interactions in experimentally simulated dirty snowball and dirty iceball cometary nuclei

In the dirty snowball model for cometary nuclei, comet-nucleus materials are regarded as mixtures of volatile ices and relatively non-volatile minerals or chemical compounds. Carbonaceous chondrite meteorites are regarded as useful analogs for the rocky component. To help elucidate the possible physical geochemistry of cometary nuclei, preliminary results are reported of calorimetric experiments with two-component systems involving carbonaceous chondrites and water ice. Based on collective knowledge of the physics of water ice, three general types of interactions can be expected between water and minerals at sub-freezing temperatures: (1) heterogeneous nucleation of ice by insoluble minerals; (2) adsorption of water vapor by hygroscopic phases; and (3) freezing- and melting-point depression of liquid water sustained by soluble minerals. The relative and absolute magnitude of all three effects are expected to vary with mineral composition.

Gooding, James L.↗