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PubMed1994

Carbonaceous components in the comet Halley dust.

Cometary grains containing large amounts of carbon and/or organic matter (CHON) were discovered by in situ measurements of comet Halley dust composition during VEGA and GIOTTO flyby missions. In this paper, we report the classification of these cometary grains by means of cluster analysis, discuss the resulting compositional groups, and compare them with substances observed or hypothesized in meteorites, interplanetary dust particles, and the interstellar medium. Grains dominated by carbon and/or organic matter (CHON grains) represent approximately 22% of the total population of measured cometary dust particles. They usually contain a minor abundance of rock-forming elements as well. Grains having organic material are relatively more abundant in the vicinity of the nucleus than in the outer regions of the coma, which suggests decomposition of the organics in the coma environment. The majority of comet Halley organic particles are multicomponent mixtures of carbon phases and organic compounds. Possibly, the cometary CHON grains may be related to kerogen material of an interstellar origin in carbonaceous meteorites. Pure carbon grains, hydrocarbons and polymers of cyanopolyynes, and multi-carbon monoxides are present in cometary dust as compositionally simple and distinctive components among a variety of others. There is no clear evidence of significant presence of pure formaldehyde or HCN polymers in Halley dust particles. The diversity of types of cometary organic compounds is consistent with the interstellar dust model of comets and probably reflects differences in composition of precursor dust. Preservation of this heterogeneity among submicron particles suggests the gentle formation of cometary nucleus by aggregation of interstellar dust in the protosolar nebula without complete mixing or chemical homogenization at the submicron level.

Astronomy↗
PubMed1988

Are there carbonate deposits in the Valles Marineris, Mars?

The thick sequences of layered deposits found in the Valles Marineris have recently been determined by S.S. Nedell, S.W. Squyres, and D.W. Andersen (1987, Icarus, 70, 409-441) to contain a minimum of approximately 10(5) km3 of material. We suggest that this material could be derived from the precipitation of 30 mbar of atmospheric CO2 as carbonates in lakes. As surface temperatures fell on Mars, the presence of an insulating ice cover would have allowed liquid water to exist, fed by transitory surface melting. Atmospheric CO2 would have accumulated in such lakes enhancing carbonate precipitation. Support for this hypothesis comes from processes that occur in the perennially frozen lakes in the dry valleys of Antarctica where the mean temperature is 253 degrees K and the lake water is supersaturated with atmospheric gases. A search of the recently reissued Mariner 6/7 infrared spectrometer data in the wavelength region between 2 and 6 micrometers failed to confirm the presence of carbonates. Due to the fact that no spectral footprints appear to directly overlie the layered deposits, and that deposits may be blanketed by an eolian mantle, this negative result is inconclusive. We feel that the canyon deposits are still a prime site for future searches for carbonates on Mars.

Antarctic Regions↗
PubMed1989

The carbon budget in the outer solar nebula.

Detailed models of the internal structures of Pluto and Charon, assuming rock and water ice as the only constituents, indicate that the mean silicate mass fraction of this two-body system is on the order of 0.7; thus the Pluto/Charon system is significantly "rockier" than the satellites of the giant planets (silicate mass fraction approximately 0.55). This compositional contrast reflects different formation mechanisms: it is likely that Pluto and Charon formed directly from the solar nebula, while the circumplanetary nebulae that produced the giant planet satellites were derived from envelopes that surrounded the forming giant planets (envelopes in which icy planetesimals dissolved more readily than rocky planetesimals). Simple cosmic abundance calculations, and the assumption that the Pluto/Charon system formed directly from solar nebula condensates, strongly suggest that the majority of the carbon in the outer solar nebula was in the form of carbon monoxide; these results are consistent with (1) inheritance from the dense molecular clouds in the interstellar medium (where CH4/CO < 10(-2) in the gas phase) and/or (2) of the Lewis and Prinn kinetic inhibition model of solar nebula chemistry. Theoretical predictions of the C/H enhancements in the atmospheres of the giant planets, when compared to the actual observed enhancements, suggest that 10%, or slightly more, of the carbon in the outer solar nebula was in the form of condensed materials (although the amount of condensed C may have dropped slightly with increasing heliocentric distance). Strict compositional limits computed for the Pluto/Charon system using the densities of CH4 and CO ices indicate that these pure ices are at best minor components in the interiors of these bodies, and imply that CH4 and CO ices were not the dominant C-bearing solids in the outer nebula. Clathrate-hydrates could not have appropriated enough CH4 or CO to be the major form of condensed carbon, although such clathrates may be necessary to explain the presence of methane on Pluto after its formation from a CO-rich nebula. Laboratory studies of carbonaceous chondrites, and spacecraft observations of Comet Halley, strongly suggest that of the remaining possibilities, organic material, rather than elemental carbon, is the most likely candidate for the dominant C-bearing solid in the outer solar nebula. We conclude that the majority of the carbon in the outer solar nebula was in gaseous CO; 10% to a few tens of percent of the C was in condensed organic materials; and at least a trace amount of carbon was in methane gas.

Carbon↗
PubMed1989

Interplanetary dust particles collected in the stratosphere: observations of atmospheric heating and constraints on their interrelationships and sources.

The majority of the interplanetary dust particles (IDPs) collected in the stratosphere belong to one of three major classes, the first two dominated by the anhydrous minerals olivine and pyroxene, and the third by hydrous layer-lattice silicates. Infrared spectroscopy and transmission electron microscopy studies show that the different IDP classes represent different types of dust that exist as individual particles in interplanetary space. The majority of the collected IDPs smaller than 30 micrometers in diameter in the layer-lattice silicate and pyroxene classes appear not to have been heated to temperatures above 600 degrees C during atmospheric entry. The relatively low maximum temperatures experienced by these IDPs during atmospheric entry imply that they arrive at the top of the atmosphere with low geocentric encounter velocities. This limits the possible encounter trajectories for these particles to relatively circular, prograde orbits. As a result, it is unlikely that these IDPs are from Earth-crossing comets or asteroids. Asteroids, and comets having low inclinations and perihelia outside 1.2 AU, appear to be the best candidates for the parent bodies of the pyroxene and layer-lattice silicate particles. Chemical and mineralogical information suggests that the pyroxene-rich IDPs are from comets and the layer-lattice silicate-rich IDPs are from asteroids. The collected IDPs dominated by olivine appear to include a larger fraction of particles heating above 600 degrees C, suggesting that these particles were captured from more eccentric orbits. This, and the observation of the infrared spectral features of olivine in several comets suggest these particles have a cometary origin. Since much of the collected dust has apparently been captured from nearly circular, prograde orbits and since there are no appropriate parent bodies presently in such orbits, these results provide an experimental confirmation that the Poynting-Robertson effect exists as a nongravitational force important in the orbital evolution of dust in the Solar System.

Atmosphere↗
PubMed1989

The thermal structure of Titan's atmosphere.

We have developed a radiative-convective model of the thermal structure of Titan's atmosphere. The model computes the solar and infrared radiation in a series of spectral intervals with vertical resolution. Sources of opacity in the visible and near infrared include stratospheric haze particles, methane cloud particles, and gaseous methane; sources of opacity in the thermal infrared include the pressure-induced opacity of N2, CH4, and H2, the permitted transitions of C2H2 and C2H6, and particulate opacity. The haze properties are determined with a simple microphysics model. The model contains a minimum of free parameters and we try to determine these by fits to independent data sets. We find that gas and haze opacity alone, with the temperatures fixed by Voyager observations, produces a model that is within a few percent of radiative convective balance everywhere in the atmosphere. In a self-consistent computation of temperatures, we find that our model calculation for the surface temperature is, in general, colder than the observed value by 5-10 degrees K. The presence or absence of methane condensation clouds only slightly alters the results. Good agreement can be obtained by adjusting the parameters in the model. The model parameters in these optimized cases are typically within 15% of the baseline values and within the limits allowed by observations. We conclude that the most important factors controlling Titan's thermal structure are absorption of sunlight by the stratospheric haze and the pressure-induced gas opacity in the infrared. Within the uncertainties of the model, these effects can explain the observed temperature profile. Condensation clouds play a minor role, if any.

Atmosphere↗
PubMed1990

The 2.5-5.0 micrometers spectra of Io: evidence for H2S and H2O frozen in SO2.

Infrared spectra of Io in the region 2.5-5.0 micrometers, including new observational data, are analyzed using detailed laboratory studies of plausible surface ices. Besides the absorption bands attributable to sulfur dioxide frosts, four infrared spectral features of Io are shown to be unidentified. These unidentified features show spatial and temporal band strength variations. One pair is centered around 3.9 micrometers (3.85 and 3.91 micrometers) and the second pair is centered around 3.0 micrometers (2.97 and 3.15 micrometers). These absorptions fall close to the fundamental stretching modes in H2S and H2O, respectively. The infrared absorption spectra of an extensive set of laboratory ices ranging from pure materials, to binary mixtures of H2S and H2O (either mixed at different concentrations or layered), to H2O:H2S:SO2 mixtures are discussed. The effects of ultraviolet irradiation (120 and 160 nm) and temperature variation (from 9 to 130 K) on the infrared spectra of the ices are examined. This comparative study of Io reflectance spectra with the laboratory mixed ice transmission data shows the following: (1) Io's surface most likely contains H2S and H2O mixed with SO2. The 3.85- and 3.91-micrometers bands in the Io spectra can be accounted for by the absorption of the S-H stretching vibration (nu 1) in H2S clusters and isolated molecules in an SO2-dominated ice. The weak 2.97- and 3.15-micrometers bands which vary spatially and temporally in the Io spectra coincide with the nu 3 and nu 1 O-H stretching vibrations of clusters of H2O molecules complexed, through hydrogen bonding and charge transfer interactions, with SO2. (2) The observations are well matched qualitatively by the transmission spectra of SO2 ices containing about 3% H2S and 0.1% H2O which have been formed by the condensation of a mixture of the gases onto a 100 K surface. (3) No new features are produced in the region 2.5 to 5.0 micrometers in the spectrum of these ices under prolonged ultraviolet irradiation or temperature variation up to 120 K. (4) Comparison of the Io spectra to transmission spectra of both mixed molecular ices and layered ices indicates that only the former can explain the shifts and splitting of the absorption bands seen in the Io spectrum and additionally can account for the fact that solid H2S is observed in the surface material of Io at temperature and pressure conditions above the sublimation point of pure H2S.

Astronomical Phenomena↗
PubMed1990

The volume- and surface-binding energies of ice systems containing CO, CO2, and H2O.

Experiments on pure CO and CO2 ices as well as on CO and CO2 in H2O-rich ices have been made in order to determine the condensation and vaporization properties of these systems. The surface- and volume-binding energies appropriate for these systems are derived, including a more precise determination of the value for CO in H2O than we have previously reported.

Carbon Dioxide↗
PubMed1990

Observations of the microwave emission of Venus from 1.3 to 3.6 cm.

Laboratory measurements of Steffes (1986) have suggested that the intensity and shape of the microwave spectrum of Venus might be especially sensitive to the subcloud abundance of constituents such as SO2 and gaseous H2SO4. It was likewise suggested that some variations of the shape of the emission spectrum might occur between 1.5 and 3 cm (10 to 20 GHz), a wavelength range which had previously only been sparsely observed. As a result, coordinated observations of Venus emission were conducted at four wavelengths between 1.35 cm (22.2 GHz) and 3.6 cm (8.42 GHz) using the 43-m NRAO antenna at Green Bank, West Virginia, and the 64-m antenna at NASA's Deep Space Communication Complex, Goldstone, California. In this paper, we report the methodology and results of these observations, and compare the results with other observations and with calculated emission spectra. We conclude that the observed emission spectrum is consistent with an average subcloud abundance of gaseous H2SO4 in equatorial and midlatitude regions which is approximately 5 ppm. It is suggested that additional measurements of atmospheric microwave opacity be made with the Pioneer-Venus Orbiter Radio Occultation experiment to search for temporal and spatial variations in gaseous H2SO4 abundance in the Venus atmosphere. An upper limit for the subcloud abundance of SO2 is also determined.

Astronomy↗
PubMed1990

Processing of refractory meteorite inclusions (CAIs) in parent-body atmospheres.

The refractory meteorite inclusions known as CAIs (calcium-aluminum rich inclusions) display melted rims that were produced by thermal events of only a few seconds duration. We show that gas dynamic deceleration in a temporary atmosphere around an accreting parent body, produced by gas release during accretion, could provide a regime of sufficiently high gas density and small scale height to achieve partial melting of the CAIs. In addition, the presence of dust in the atmosphere would increase the gradient of pressure with height (i.e., effectively reduce the scale height), lower the rate of blowoff (thus keeping more gas around the body), as well as allow dust particles to become trapped in the partially melted material as is observed in some cases. Thus, CAIs may be regarded as probes of a primitive atmosphere by virtue of the thermal and mineralogical alteration that occurred upon their passage through the atmosphere.

Aluminum↗
PubMed1990

Earth analogs for Martian life. Microbes in evaporites, a new model system for life on Mars.

The prospect of life on Mars today is daunting. Especially problematic for a potential life form is a lack of water, particularly in a liquid state; extremely cold temperatures; ultraviolet and ionizing radiation; and soil oxidants. Yet, "oases" where life might persist have been suggested to occur in rocks (in analogy with endolithic microorganisms described from deserts around the world), in polar ice caps (in analogy with snow and ice algae) and in possible volcanic regions (in analogy with chemoautotrophs living in deep sea hydrothermal vents); all are critically examined. Microorganisms are known to be able to survive in salt crystals, and recently it has been shown that organisms can metabolize while encrusted in evaporites. Because evaporites are thought to occur on Mars and can attenuate light in the UV range while being far more transparent to radiation useful for photosynthesis (400-700 nm), and because of the properties of these "endoevaporitic" organisms, I propose that such communities provide a new model system for studying potential life on Mars. On the basis of this model, I suggest possibilities for site selection for future exobiological experiments on Mars.

Atmosphere↗
PubMed1991

UV spectroscopy of Titan's atmosphere, planetary organic chemistry and prebiological synthesis. II. Interpretation of new IUE observations in the 220-335 nm range.

We report on new observations of Titan with the International Ultraviolet Explorer in the mid-UV range (lambda approximately 220-335 nm). We use these data to determine upper limits for the abundances of simple organic compounds in the gas phase and to further constrain the properties of the high altitude haze on Titan. As a baseline, we adopted the parametrized microphysical model of McKay et al. (1989) which is successful at reproducing Titan's thermal structure while satisfying several other observational constraints in the visible and IR regions. However, we find that such a model--in which all particles at a given altitude are assumed to have the same size--cannot match simultaneously the IUE observations and the visible/IR data, even when allowance is made for a wide range of values in the adjustable parameters. On the other hand, a good overall agreement is obtained when considering a biomodal size distribution, with small haze particles or "polymers" (r < 0.02 micrometer) acting as strong Rayleigh absorbers below 300 nm and larger haze particles (r approximately 0.1-0.5 micrometer) being responsible for the characteristics of the albedo spectrum in the near-UV, visible, and IR regions. This approach is consistent with the results of several previous investigations of the properties of Titan's haze, although our preferred vertical structure for the haze + polymer material somewhat differs from earlier solutions. On the basis of simple dynamical considerations, we adopted a uniformly mixed layer between 150 and 600 km. The IUE data allow us to place fairly stringent constraints on the abundance of the Rayleigh absorbers, if we assume that their optical properties are similar to those of laboratory-synthesized "tholins": The column-mass density of this material--the essential observable that can be determined from our study--is of the order of 5 micrograms cm-2. This would correspond to number-densities between 10(3) and 10(7) cm-3 in the 150-600 km altitude range, if the average particle radius is between 0.001 and 0.02 micrometer. Such high number densities are a priori at odds with the estimated coagulation lifetime for particles of that size. Thus, our proposed bimodal size distribution is plausible only if inhibiting processes act to slow down considerably the coagulation of polymers in Titan's stratosphere.

Acetylene↗
PubMed1991

Duration of liquid water habitats on early Mars.

We have employed a simple climate model of early Mars in order to estimate the duration of ice-covered lakes after the onset of freezing conditions on Mars. The critical parameter determining the existence of ice-covered lakes is the existence of peak seasonal temperatures above freezing. The peak temperature occurs at the subsolar point at perihelion. We use the weathering model of Pollack et al. (Icarus 71, 203-224, 1987) to compute the pressure and temperature evolution of the atmosphere. We have included the variability of the solar luminosity. We find that if there was a source of ice to provide meltwater, liquid water habitats could have been maintained under relatively thin ice covers for up to 700 million years after mean global temperatures fell below the freezing point. At this point, the mean annual temperature is 227 K, and the pressure of atmospheric CO2 is about 0.5 bar. Without the presence of stable bodies of liquid water, it is not clear what mechanisms were responsible for the removal of this remaining CO2. From a biological point of view, we find that the duration of liquid water habitats on early Mars exceeds the upper limit on the time required for the origin of life on Mars.

Atmosphere↗
PubMed1991

Are some chondrule rims formed by impact processes? Observations and experiments.

Observations and experimental evidence are presented to support the hypothesis that high-speed impact into a parent body regolith can best explain certain textures and compositions observed for rims on some chondrules. A study of 19 interclastic rimmed chondrules in the Weston (H 3/4) ordinary chondrite shows that two main rim types are present on porphyritic olivine-pyroxene (POP) and porphyritic pyroxene (PP) chondrules: granular and opaque rims. Granular rims are composed of welded, fine-grained host chondrule fragments. Bulk compositions of granular rims vary among chondrules, but each rim is compositionally dependent on that of the host chondrule. Opaque rims contain mineral and glass compositions distinctly different from those of the host, partially reacted chondrule mantle components, and some matrix grains. Opaque rims are greatly enriched in FeO (up to 63 wt%). The original chondrule pyroxene compositional zonation patterns and euhedral grain outlines are discontinuous at the chondrule/rim interface. Opaque rims are dominated by fayalitic olivine (Fa92-56), with high Al2O3 content (0.78-3.15%), which makes them distinctly different from primary olivine, but similar to Fe-olivine in chondrule rims of other meteorites. Thin zones of chondrule minerals adjacent to the present rims are intermediate in FeO content between the Mg-rich interior and the Fe-rich rim, which indicates a reaction relationship. Regardless of conclusions drawn regarding other types of rims, granular and opaque rim characteristics appear to be inconsistent with nebular condensation, in that host and matrix fragments are included within the rim. We have initiated a series of experiments, using the Ames two-stage light gas gun, to investigate the hypothesis that the Weston chondrule rims are the result of thermal and mechanical alteration upon impact into a low-density medium. Clusters of approximately 200-micron-sized silicate particles were fired into aerogel (density = 0.1 g cm-3) at velocities of 5.6, 4.7, and 2.2 km sec-1. Recovered grains show characteristics that range from fragmented projectile grains mixed with melted aerogel that nearly rim the grains to grains that have melted aerogel clumps mixed with partially melted projectile. These experimental results demonstrate that rim-like thermal and mechanical alteration of projectiles can result from a high-velocity encounter with a low-density target. Therefore, experiments using appropriately chosen projectile and target materials can provide a test of the hypothesis that chondrule rims common to Weston and possibly other ordinary chondrites were formed by such a process.

Astronomical Phenomena↗
PubMed1991

Urey Prize Lecture: Planetary Evolution and the Origin of Life.

The origin of life appears to be closely tied to the formation and early evolution of the solar system. Key questions deal with the source of abiotic organic material on the early Earth, the nature of interstellar organic material and its relationship to the observed organic compounds in the outer solar system, and the possible origin of life on Mars early in its history. From the perspective of planetary environments, liquid water is the essential requirement for life and serves as a surrogate indicator for life. New models and analyses in conjunction with data returned from upcoming missions promise to significantly advance our knowledge of how life originated in our solar system.

Awards and Prizes↗
PubMed1991

Laboratory studies of the newly discovered infrared band at 4705.2 cm-1 (2.1253 micrometers) in the spectrum of Io: the tentative identification of CO2.

We discuss over 120 laboratory experiments pertaining to the identification of the new absorption band discovered by Trafton et al. (1991) at 4705.2 cm-1 (2.1253 micrometers) in the spectrum of Io. It is shown that this band is not due to overtones or combinations of the fundamental bands associated with the molecules (or their chemical complexes) already identified on Io, namely, SO2, H2S, and H2O. Thus, this band is due to a new, previously unidentified, component of Io. Experiments also demonstrate that the band is not due to molecular H2 frozen in SO2 frosts. Since the frequency of this band is very close to the first overtone of the nu 3 asymmetric stretching mode of CO2, we have investigated the spectral behavior of CO2 under a variety of conditions appropriate for Io. The profile of the Io band is not consistent with the rotational envelope expected for single, freely rotating, gaseous CO2 under Io-like conditions. It was found that pure, solid CO2 and CO2 intimately mixed in a matrix of solid SO2 and H2S produce bands with similar widths (5-10 cm-1), but that these bands consistently fall at frequencies about 10-20 cm-1 (approximately 0.007 micrometer) lower than the Io band. CO2 in SO2 : H2S ices also produces several additional bands that are not in the Io spectra. The spectral fit improves, however, as the CO2 concentration in SO2 increases, suggesting that CO2-CO2 interactions might be involved. A series of Ar : CO2 and Kr : CO2 matrix isolation experiments, as well as laboratory work done elsewhere, show that CO2 clustering shifts the band position to higher frequencies and provides a better fit to the Io band. Various laboratory experiments have shown that gaseous CO2 molecules have a propensity to cluster between 80 and 100 K, temperatures similar to those found on the colder regions of Io. We thus tentatively identify the newly discovered Io band at 4705.2 cm-1 (2.1253 micrometers) with CO2 multimers or "clusters" on Io. Whether these clusters are buried within an SO2 frost, reside on the surface, or are in a residual, steady-state "atmospheric aerosol" population over local coldtraps is not entirely clear, although we presently favor the latter possibility. The size of these clusters is not well defined, but evidence suggests groups of more than four molecules are required. The absorption strength of the 2 nu 3 CO2 cluster overtone determined in the laboratory, in conjunction with the observed strength of the Io band, suggests that the disk-integrated abundance of CO2 is less than 1% that of the SO2. Studies of the sublimation behavior of CO2 indicate that it probably resides predominantly in the cooler areas (< 100 K) of Io. The relative constancy of the Io feature over a variety of orbital phases suggests that the polar regions may contain much of the material. Some consequences of the physical properties of CO2 under conditions pertinent to Io are discussed. The presence of CO2 clusters on Io could be verified by the detection of any one of several other infrared bands associated with the CO2 molecule, of which the strongest are the nu 3 12CO2 asymmetric stretch fundamental near 2350 cm-1 (4.25 micrometers) and the nu 2 bending mode fundamental near 660 cm-1 (15.1 micrometers). Weaker bands that may also be detectable include the nu 3 13CO2 asymmetric stretch fundamental near 2280 cm-1 (4.39 micrometers), the 2 nu 2 + nu 3 combination/overtone band near 3600 cm-1 (2.78 micrometers), and the nu 1 + nu 3 combination band near 3705 cm-1 (2.70 micrometers).

Astronomical Phenomena↗
PubMed1991

A new class of absorption feature in Io's near-infrared spectrum.

We report our discovery of an absorption feature in the infrared spectrum of Io centered at 2.1253 micrometers (4705.2 cm-1). This band is marginally resolved at resolving power 1200 with a deconvolved full width at half-maximum (FWHM) of about 4 cm-1. This contrasts with the 30- to 50-cm-1 widths of the broad absorption features previously detected at longer wavelengths which arise from mixtures of SO2 with H2S and H2O. This newly discovered feature is relatively weak, having a core only 5% below the continuum at this resolving power. Our survey from 1.98 to 2.46 micrometers (5050-4065 cm-1) at this same resolving power revealed no other feature greater than 1% of the continuum level shortward of 2.35 micrometers, and 3% elsewhere. The feature does not correspond to any gas- or solid-phase absorption that might be expected from previously identified constituents of Io's surface. No temporal or longitudinal variation has been detected in the course of 18 nights of observation over the past year and no significant variation in the strength of the feature was seen during an emergence from eclipse. These observations indicate that the source material of the feature is reasonably stable, and is more uniformly distributed in longitude than Io's hot spots. These characteristics all indicate that the feature belongs to a class different from those characterizing other known absorption features in Io's spectrum. Consequently, it should reveal important new information about Io's atmosphere-surface composition and interaction. A series of laboratory experiments of plausible surface ices indicates that (i) the band does not arise from overtones or combinations of any of the molecular vibrations associated with species already identified on Io (SO2, H2S, H2O) or from chemical complexes of these molecules, (ii) the band does not arise from H2 trapped in SO2, and (iii) the band may arise from the 2 nu3 mode of CO2. If the band arises from CO2, it is clear from its detailed shape and position that the molecules are not embedded in an SO2 matrix, as are H2S and H2O, but may be present as multimers or "clusters."

Atmosphere↗
PubMed1991

Solid C triple bond N bearing material on outer solar system bodies.

Using telescopic observations by ourselves and other observers, we have identified cyano-group containing molecules in the very dark solids on the surfaces of a few D-class asteroids, the dust of some comets, and low-albedo hemisphere of Iapetus, and the rings of Uranus, through spectroscopic detection of the 2.2-micrometers overtone of the C triple bond N stretching fundamental mode. The occurrence of this band on all four classes of small Solar System bodies may be diagnostic of the duration of exposure and degree of modification of surface materials, and may also establish a link between outer Solar System and interstellar materials.

Carbon↗
PubMed1992

On the possibility of chemosynthetic ecosystems in subsurface habitats on Mars.

We have reexamined the question of extant microbial life on Mars in light of the most recent information about the planet and recently discovered nonphotosynthetic microbial ecosystems on Earth--deep sea hydrothermal vent communities and deep subsurface aquifer communities. On Mars, protected subsurface niches associated with hydrothermal activity could have continued to support life even after surface conditions became inhospitable. Geochemical evidence from the SNC meteorites and geomorphological evidence for recent volcanism suggest that such habitats could persist to the present time. There are also extensive geological features that attest to the ubiquitous nature of volcano-ground ice interactions on Mars. We suggest a possible deep subsurface microbial ecology similar to those discovered to depths of several kilometers below the surface of the Earth. We focus on anaerobic systems utilizing CO2 as the primary source of carbon. Liquid water could be provided by the heat of geothermal or volcanic activity melting permafrost or other subsurface water sources. Gases from volcanic activity deep in the planet could provide reducing power (as CH4, H2, or H2S) percolating up from below and enabling the development of a microbial community based upon chemolithoautotrophy. We suggest a methanogen (or acetogen) and sulfur-based microbial ecology as one possible basis for microbial primary production. Our hypothetical ecosystem is neither supported, nor excluded, by current observations of Mars. Tests for such a subsurface system involve locating active geothermal areas associated with ground ice or detecting trace quantities of reduced atmospheric gases that would leak from such a system.

Carbon Dioxide↗