bluuebunny/crossref_metadata_2025 huggingface dataset:
Latitudinal temperature gradients and climate change
Authors: Rind D.
Published: February 2004

The effects of a change in the latitudinal sea surface temperature gradient are investigated in several GCM experiments. Sea surface temperatures are increased/decreased in the tropics and polar regions, with little change in the global average surface air temperature. Then the experiments are repeated with colder/warmer conditions globally. Expectations generated from these runs are compared with the resulting climate changes in a doubled CO2 experiment and show overall agreement. Results show that the latitudinal temperature gradient governs the Hadley cell intensity, eddy energy properties, and eddy transports other than latent heat. The global mean temperature governs moisture and cloud cover, Hadley cell extent, and total rainfall. The degree of tropical and subtropical moisture changes depend on both the latitudinal gradient and the mean temperature. The Aleutian low is particularly sensitive to gradient changes, while the Icelandic low (and therefore the Greenland ice core region) is not, possibly due to orographically induced constraints in the North Atlantic. The results are then compared with paleoclimate evidence to deduce what has happened to latitudinal gradients and climate in the past. It is estimated that low‐latitude temperature gradients similar to today's may have occurred in the Mesozoic and in the Little Ice Age; reduced gradients were more likely in the Pliocene, Eocene, Younger Dryas, and Last Glacial Maximum. At higher latitudes, warm climates likely had reduced temperature gradients, and cold climates increased gradients. Observed equator to pole gradients were increased in the 1980s relative to the 1950s, and the simulated climate changes consistent with observations include warming of Alaska and Asia, drying in the subtropics, and moisture variability in the United States. Assignment of causes to past latitudinal gradient changes is problematic due to uncertainties concerning CO2 and ocean heat transports, but tentative conclusions based on this analysis support the likelihood of a future, higher‐CO2 climate exhibiting a large low‐latitude gradient and ample precipitation at middle latitudes.
Trend analysis of the homogenized total ozone series of Arosa (Switzerland), 1926–1996
Authors: Staehelin Johannes , Kegel Rainer , Harris Neil R. P.
Published: February 2004

Total ozone measurements have been made at Arosa, Switzerland (47°N), from 1926 through the present day, forming the longest total ozone series in the world. The record has been recently homogenized. Ozone trends are calculated to be −(2.3±0.6)% per decade for annual means (larger losses are found in winter and spring, approximately −4% per decade for trends in January, February, and March) when a simple linear change from 1970 to 1996 is assumed. In addition, total ozone trends are calculated using multiple regression models involving combinations of explanatory variables for the 11‐year solar cycle, local meteorological conditions (the Mount Säntis high‐altitude temperature record), stratospheric aerosol loading from volcanoes, and stratospheric chlorine loading. When the terms for the solar cycle, the stratospheric aerosol loading and the high mountain temperature record were included, the annually averaged ozone trends were found to be −(1.9±0.6)% per decade. While a statistically significant relation is found between total ozone and indices of aerosol loadings of the stratosphere, the recent decrease in total ozone cannot be accounted for by the higher average aerosol content in the second half of the century. Finally, the decrease in ozone in the stratosphere is estimated to be approximately 30% larger than that found for total ozone, when a crude estimate of the increase in tropospheric ozone is included. The acceleration observed in total ozone trends between the 1970s and the 1980s over northern midlatitudes [e.g., Harris et al., 1997] might be partially attributed to the larger increase in tropospheric ozone in the 1970s.
Tropospheric ozone production and transport in the springtime in east Asia
Authors: Carmichael Gregory R. , Uno Itsushi , Phadnis Mahesh J. , Zhang Yang , Sunwoo Young
Published: February 2004

Ozone transport and chemistry in the springtime in east Asia are studied by use of the STEM‐II (Sulfur Transport Eulerian Model) regional‐scale transport/chemistry model. Three‐dimensional simulations are performed for the period May 1–15, 1987. This was a period of strong downward transport of ozone in east Asia, associated with traveling low‐pressure systems. Elevated ozone levels were observed at high‐altitude surface sites in Japan during this period. Model simulations both with and without photochemical processes are performed in order to assess the relative importance of the transport and chemical sources of tropospheric ozone. The model results are compared with measured values at a network of stations in Japan and are found to accurately capture most of the important observed features. Near‐surface ozone levels are found to be strongly influenced both by continental outflow of precursors occurring behind the cold fronts as they move out over the Pacific Ocean and by the strong downward transport of ozone‐rich air from the upper troposphere which occurs in association with these weather systems.
High northern latitude forest fires and vegetation emissions over the last millennium inferred from the chemistry of a central Greenland ice core
Authors: Savarino Joel , Legrand Michel
Published: February 2004

We have analyzed the soluble portion of impurities trapped in solid precipitation that accumulated at Summit (central Greenland) from 1193 A.D. to the present. Seventy‐three ice layers show elevated concentrations of ammonium and formate, caused by high‐latitude biomass burning debris reaching Greenland. While a mixture of ammonium and formate close to the molar ratio is generally observed in these ice layers, a large depletion of formate relative to ammonium is found in a few cases. The chemical composition of such layers indicates the presence of a mixture of ammonium, formate, and nitrate with a NH4+/(HCOO−+NO3−) molar ratio close to 1. These differences may be related to the fire type (flaming versus smoldering) or to meteorological conditions encountered by plumes during their transport toward Greenland. The high‐resolution ammonium and formate profiles are used to reconstruct the frequency and the intensity of high‐latitude biomass burning input having reached central Greenland since 1193 A.D. Three periods of enhanced biomass burning input over central Greenland are identified: 1200–1350 A.D., 1830–1930 A.D., and to a lesser extent 1500–1600 A.D. The 1200–1350 A.D. time period coincides with warm and dry conditions which characterized the Medieval Warm Period. After a period of infrequent biomass burning input during the coldest period of the Little Ice Age (1600–1850 A.D.), the frequency was enhanced at the turn of the last century and then decreased throughout this last century. Aside from high‐latitude biomass burning, the background levels of formate show a slight and persistent decreasing trend over the last 800 years probably reflecting the deterioration of the boreal vegetation from North America.
Chemical conversion of subsonic aircraft emissions in the dispersing plume: Calculation of effective emission indices
Authors: Petry H. , Hendricks J. , Möllhoff M. , Lippert E. , Meier A. , Ebel A. , Sausen R.
Published: February 2004

A box model representative for a mesoscale volume and three different plume models are used to estimate the chemical conversion of exhaust species of a subsonic aircraft at cruise altitude. Clearly deviating results have been obtained for instantaneous mixing of the exhaust in a box and gradual dispersion of a plume. The effect of varying daytime of release as well as the impact of changing dispersion time is studied with emphasis on the aircraft‐induced O3 production. Effective emission indices are calculated which enable a correction for expanding plume effects in global or mesoscale models.
Formation mechanisms and chemical characteristics of elevated photochemical layers over the northeast United States
Authors: Berkowitz Carl M. , Fast Jerome D. , Springston Stephen R. , Larsen Richard J. , Spicer Chester W. , Doskey Paul V. , Hubbe John M. , Plastridge Robert
Published: February 2004

The chemical composition of layers of trace gas mixtures within the lower troposphere and their relationship to surface trace gas concentrations are investigated using airborne chemistry and meteorological measurements made over eastern Connecticut and central Massachusetts. Layers of photochemically aged material were identified by maxima above the surface stable layer in the profiles of O3, NOy, CO, aerosols, peroxyacetyl nitrate (PAN), and the ratio of highly to lesser reactive hydrocarbons (e.g., benzene and toluene). Observations suggest that strong diurnal variations in surface‐ozone mixing ratios are associated with elevated layers of ozone and other trace gases. The elevated layers were also associated with strong gradients of NOx both vertically, across the mixed layer, and horizontally, between urban and rural regions, providing evidence for the dominant role of localized anthropogenic NOx emissions over North America on ozone production in urban regions. On days when elevated layers were detected, isoprene's late‐morning propene‐equivalent mixing ratio (a measure of nonmethane hydrocarbon reactivity with OH) was an order of magnitude greater than that of the next most reactive species up to an altitude of 650 m mean sea level. Four‐dimensional data assimilation was used within a mesoscale model to study the formation mechanism and history of these layers, with a key result being that no unique “age” or source region could generally be attributed to these layers as a consequence of turbulent mixing and transport leading to their formation.
Eruption constraints on tube‐fed planetary lava flows
Authors: Sakimoto Susan E. H. , Crisp Joy , Baloga Stephen M.
Published: February 2004

We examine the role of pressure and gravity as driving forces in planetary lava tubes for Newtonian and power law rheologies. The tubes are assumed to have been filled with lava that was emplaced in constant diameter circular tubes in the laminar flow regime and had constant density, heat capacity, thermal conductivity, and viscosity. Our model provides relationships between tube dimensions, driving forces, and effusion rates and rheology parameters. In general, the pressure term in the driving force dominates for very small slopes, but the gravity term eclipses the pressure term as the slope increases. Applying the model to Alba Patera tube flows suggests effusion rates somewhere between 2 and 105 m3/s and viscosities between 102 and 106 Pa s, with tighter constraints (2 to 4 orders of magnitude) for specific tube sizes and travel times. These effusion rate results are lower and the viscosity ranges are higher than those found in previous studies. This allows eruptions that are closer in style to terrestrial basaltic eruptions, although the flows are still considerably larger in scale than the Hawaiian tube flows. We find that very low lava viscosities are not essential for Alba Patera lava tubes and that tube formation may be a better indicator of the steadiness of the eruption and the presence of low slopes than it is of low viscosities (e.g., 102 Pa s). In addition, this analysis suggests that the tube systems on the steep flanks of Olympus Mons are fundamentally different from those at Alba Patera. The Olympus Mons flows could not have roofed over, been continuously full, or maintained a continuous lava tube transport system in the assumed full, steady, and fully developed conditions.
Chemical studies of H chondrites 8. On contemporary meteoroid streams
Authors: Wolf Stephen F. , Wang Ming‐Sheng , Dodd Robert T. , Lipschutz Michael E.
Published: February 2004

Using date and time of fall and petrographic classification as criteria, many equilibrated H chondrites that fell during September and October from 1812 to the present form four significant clusters, denoted as Cluster 2 through Cluster 5, on day‐year plots. Using radiochemical neutron activation analysis, we determined 15 trace elements, U, Au, Co, Sb, Ga, Rb, Ag, Se, Cs, Te, Zn, Cd, Bi, Tl, and In (ordered by increasing putative volatility during nebular condensation), in 27 members of these four clusters. We used model‐dependent and model‐independent multivariate statistical techniques to compare contents of the 10 most volatile elements separately in the four clusters with those of a 33‐member suite of random H chondrite falls (from 1773 to 1970). The Clusters 2 and 5 suites (that fell in September 1880–1991 and October, 1919–1984, respectively), each of which is represented by 10 H chondrite falls, are not compositionally distinguishable from the suite of random falls. However, the 17‐member combined suite of Clusters 3 and 4 chondrites (that fell during September–October, 1812–1992) proves compositionally distinguishable from random falls at moderate to strong significance levels of 0.01–0.001. This 17‐member suite is less readily distinguished from random falls than are the previously reported suite of Cluster 1 falls (May 1855–1895), or Antarctic H chondrites with nominal terrestrial ages >50 kyr, each of which is highly significant at <0.001 levels. All suites are genomict and exhibit a range of cosmic ray exposure ages with a plurality having 6–8 Ma ages. Inconclusive results are obtained in the cases of Clusters 2 and 5. However, three H chondrite suites (Clusters 1,3, and 4) distinguishable from the random background by one property (time of fall) are also distinguishable by another (contents of volatile trace elements or thermal history). Temporal change of H chondrite sources sampled by Earth are indicated by these data.
A biwavelength analysis of Pioneer Venus polarization observations
Authors: Knibbe Willem Jan J. , de Haan Johan F. , Hovenier Joop W. , Travis Larry D.
Published: February 2004

A new method for analyzing Pioneer Venus polarimetry data on a pixel‐wise basis is presented. Quasi‐simultaneous observations at two wavelengths (550 and 935 nm) are combined and compared with results of multiple scattering calculations. In this manner, hypotheses about particle size distributions in the upper part of the Venus atmosphere are tested. Particles composed of a sulfuric acid solution are considered, and a distinction is made between large and small particles, called cloud and haze particles, respectively. Three model atmospheres have been investigated: (1) a single layer containing cloud particles, (2) a single layer containing a mixture of cloud and haze particles, and (3) a two layer model with an upper layer composed of haze particles and a lower layer containing cloud particles. It is found that all three models agree with the observations at phase angles near 20°, but that the first model cannot be made to agree with the observations for phase angles near 90°. This confirms the presence of haze particles in the Venus atmosphere found earlier by Kawabata et al. [1980]. We find that the haze particles may be situated either above or mixed within the main cloud deck of Venus. We derived effective radii between 0.85 and 1.15 μm for the cloud particles, and effective radii of 0.2 or 0.3 μm for the haze particles. When the haze particles are situated above the cloud layer, the haze optical thickness can take values of up to 0.6 at 550 nm. When the haze particles are mixed with the cloud particles, their contribution to the total atmospheric scattering coefficient at 550 nm can become as large as 70%.
A carbon and nitrogen isotope study of Zagami
Authors: Grady Monica M. , Wright I. P. , Pillinger C. T.
Published: February 2004

Samples from the two major lithologies (fine‐ and coarse‐grained) in Zagami have been analyzed for the abundance of carbon and nitrogen and their isotopic compositions. Using the technique of stepped combustion, it was possible to evaluate the distribution of carbon and nitrogen within different species (organic, carbonate, nitrate, etc.) in the samples. Separates of shock‐produced glass and pigeonite were also analyzed for carbon. The majority of the carbon and nitrogen in each sample arises from contaminants (organic materials, absorbed gases, etc.). However, carbon and nitrogen of magmatic origin is released above 600°C (δ13C ∼−24‰; δ15N ∼−5‰). The glass separates contain a minor contribution from trapped Martian atmospheric CO2, in addition to the magmatic component. Zagami appears to contain two generations of carbonate, an isotopically light end‐member with minimum δ13C around −23‰, plus a more 13C‐enriched carbonate. The latter is typical of Martian carbonates formed from fluid in contact with Martian atmospheric CO2, while the former might represent a more primitive source of carbon, and possibly emanate from the carbonate anion present within silicates or phosphates. The spread in δ13C values of carbonates in Martian meteorites clearly points to the operation of at least two processes, each imparting a characteristic carbon isotopic signature. These processes are interpreted within the framework of models that describe the evolution of Zagami‐type basalts on Mars.
On the role of thermal conductivity on thermal erosion by lava
Authors: Bussey D. B. J. , Guest J. E. , Sørensen S.‐A.
Published: February 2004

Lava channels are abundant on the surface of both the Moon and Venus. There is evidence that erosion may have played a part in their formation. Here a study of the relationship between thermal conductivity and erosion rate is presented. A numerical model is used to investigate the sensitivity of the erosion rate to the relative value of the thermal conductivity of the lava, solid substrate and liquid substrate boundary layer. Results show that the highest rates for thermal erosion are achieved by a high liquid substrate and low solid substrate thermal conductivity, and that the thermal erosion process is most sensitive to the liquid substrate's thermal conductivity.
Solar‐like trapped noble gases in the Brenham pallasite
Authors: Mathew K. J. , Begemann F.
Published: February 2004

The isotopic composition of trapped neon in the Brenham pallasite is solar (20Ne/22Ne=12.9±0.3), with contributions from a cosmogenic component. The carrier of the solar neon is an acid‐soluble minor phase of the meteorite that is inhomogeneously distributed. There are excesses at 4He over the cosmogenic component, presumably radiogenic; the highest measured 4He, however, is lower than what is expected from bulk uranium and thorium concentrations. Trapped Ar is more retentively sited than the solar Ne component. Trapped Kr is isotopically similar to that in the terrestrial atmosphere, to solar, or to ureilite Kr with contributions from spallation and (n, γ)‐capture reactions on Br. The trapped Xe in this meteorite is solar, with about 20% atmospheric Xe. The heavy Xe isotopic ratios are modified by in situ decay of 244Pu, and the light Xe isotopic ratios by low‐energy proton induced production of these isotopes from Te. The presence of this component is an indication that a low‐energy proton environment prevailed in the early solar system. More detailed analysis of Brenham samples, in particular, determining whether the excesses at light Xe isotopes are correlated with trapped Xe or with Te content may provide clues to the conditions under which the proton irradiation took place. Overabundances at 129Xe from now extinct 129I are marginal. Since the trapping of noble gases necessarily preceded the formation of the meteorite itself, it is suggested that the trapped Ne isotopic composition as measured in Brenham represents the Ne isotopic composition of ancient solar gases. Elemental ratios suggest noble gases to be a mixture of “planetary” and solar components. The Kr and Xe isotopic compositions of Springwater pallasite are markedly modified by contributions from a cosmogenic component, and the light noble gases are dominated by spallation products. This meteorite does not show any evidence for trapped Ne, solar or otherwise.
Initial data from the Mars Global Surveyor thermal emission spectrometer experiment: Observations of the Earth
Authors: Christensen Philip R. , Pearl John C.
Published: February 2004

The thermal emission spectrometer (TES) on the Mars Global Surveyor spacecraft acquired observations of the Earth from a distance of 4.7 million km for instrument performance characterization on November 24, 1996. The data were calibrated using an internal reference surface and deep space in a manner identical to that which will be used in Mars orbit, and scaled to account for the fact the Earth filled only 9.3% of the field of view. These first, calibrated, in‐flight spectra from the TES confirm the expected instrument performance and radiometric accuracy and precision. The data provide the first known whole‐disk thermal infrared spectral observations of the Earth. These spectra represent how an Earth‐like planet would appear during a search for “extrasolar” planets. Spectral features in the Earth's atmosphere are readily apparent; CO2 (centered at 668 cm−1), ozone (1000–1075 cm−1), and water vapor (200–550 and 1260–1650 cm−1) absorptions are evident. Radiation at the center of the CO2 band arises mainly from the lower stratosphere; near 650 and 700 cm−1 from near the tropopause; and further into the band wings from the troposphere and surface. Thus, in the disk‐averaged sense, the spectrum indicates a warm stratosphere above a tropopause somewhat colder than 215 K, in good agreement with results from similar instruments previously flown in low Earth orbit. The atmospheric window between approximately 800 and 1200 cm−1 is relatively featureless, as expected, given the observing geometry centered over the Pacific Ocean and the partial obscuration by clouds. The derived window brightness temperature, assuming an emissivity of unity, is 270 K, a reasonable average temperature of the ocean surface, the polar regions, and the cloud tops, especially given the uncertainties in the exact scaling to account for the fact that the Earth did not fill the field of view.
A new interpretation of scattered light measurements at Titan's limb
Authors: Rannou Pascal , Cabane Michel , Botet Robert , Chassefière Eric
Published: February 2004

Images of Titan, taken by Voyager 2 at phase angles Φ=140° and Φ=155° have provided radial intensity profiles at the bright and dark limbs, which provide information on the vertical and latitudinal distribution of organic hazes. In previous work, the deduced extinction coefficient, using ad hoc particle sizes, was obtained without help of microphysics, and it appeared difficult to compare it with coefficients computed from theoretical models. We use here our fractal approach of microphysical modeling and optics of agregates to compute intensity profiles of the main haze at the bright limb, and compare to the Voyager observations. Fractal aerosol distributions are obtained using different production altitudes and rates. Scattering and absorption of light are described by an improved model, based on the use of fractal aggregates made of spherical (Mie) particles. We show that the fractal dimension of aggregates has to be Df≈2, as predicted by microphysical arguments. Only a production altitude z0≈385±60 km, corresponding to a monomer radius rm≈0.066 μm, is fully consistent with both phase angle data. We also point out that the production rate of the aerosols decreases by a factor ≈2 between 30°S and the midnorthern latitude and further, increases up to 80°N. The average value of the production rate is Q≈1.4×10−13 kg/m2/s; we give arguments in favor of dynamical processes rather than of a purely microphysical mechanisms to explain such latitudinal variations.
Regolith composition and structure in the lunar maria: Results of long‐wavelength radar studies
Authors: Campbell Bruce A. , Hawke B. Ray , Thompson Thomas W.
Published: February 2004

Radar measurements at 70‐cm and 7.5‐m wavelengths provide insight into the structure and composition of the upper 5–100 m of the lunar regolith and crust. We combine high‐resolution (3–5 km) 70‐cm radar data for the nearside with earlier calibrated full‐disk observations at the same wavelength to provide a reasonable estimate of the lunar backscatter coefficient. These data are tested against models for echoes from a buried substrate and Mie scattering from surface and buried rocks. These mechanisms are expected to dominate the 70‐cm radar echo, with their relative importance determined by the rock population, regolith depth, substrate roughness, and the loss tangent of the soil. Results indicate that the 70‐cm radar echo for the maria comes largely from Mie scattering by rocks buried within the fine soil. Radar scattering from a buried substrate is not likely to greatly affect the observed return. We also compared the 70‐cm and 7.5‐m radar images to infrared eclipse temperature maps, crater‐population age estimates for the maria, and to TiO2 and FeO abundances inferred from Earth‐based telescopic and Clementine multispectral observations. These data imply that (1) the TiO2 (ilmenite) content of the regolith controls variations in 70‐cm depolarized echo strength among mare units, with higher titanium abundance leading to lower echoes; (2) changes in the average 70‐cm return for a given TiO2 abundance between maria of different ages do occur, but uncertainties in the current radar data do not allow us to uniquely distinguish between variations in rock population with age and calibration effects; (3) the 7.5‐m radar echoes are controlled by the age of the mare basalt flows, with older deposits having a greater degree of fracturing and higher backscatter. Future mapping at 12.6‐cm and 70‐cm wavelengths will help to resolve some of the issues raised here.
The NEAR laser ranging investigation
Authors: Zuber M. T. , Smith D. E. , Cheng A. F. , Cole T. D.
Published: February 2004

The objective of the Near‐Earth Asteroid Rendezvous (NEAR) laser ranging investigation is to obtain high integrity profiles and grids of topography for use in geophysical, geodetic and geological studies of asteroid 433 Eros. The NEAR laser rangefinder (NLR) will determine the slant range of the NEAR spacecraft to the asteroid surface by measuring precisely the round trip time of flight of individual laser pulses. Ranges will be converted to planetary radii measured with respect to the asteroid center of mass by subtracting the spacecraft orbit determined from X band Doppler tracking. The principal components of the NLR include a 1064 nm Cr:Nd:YAG laser, a gold‐coated aluminum Dall‐Kirkham Cassegrain telescope, an enhanced silicon avalanche photodiode hybrid detector, a 480‐MHz crystal oscillator, and a digital processing unit. The instrument has a continuous in‐flight calibration capability using a fiber‐optic delay assembly. The single shot vertical resolution of the NLR is <6 m, and the absolute accuracy of the global grid will be ∼ 10 m with respect to the asteroid center of mass. For the current mission orbital scenario, the laser spot size on the surface of Eros will vary from ∼4–11 m, and the along‐track resolution for the nominal pulse repetition rate of 1 Hz will be approximately comparable to the spot size, resulting in contiguous along‐track profiles. The across‐track resolution will depend on the orbital mapping scenario, but will likely be <500 m, which will define the spatial resolution of the global topographic model. Planned science investigations include global‐scale analyses related to collisional and impact history and internal density distribution that utilize topographic grids as well as spherical harmonic topographic models that will be analyzed jointly with gravity at commensurate resolution. Attempts will be made to detect possible subtle time variations in internal structure that may be present if Eros is not a single coherent body, by analysis of low degree and order spherical harmonic coefficients. Local‐ to regional‐scale analyses will utilize high‐resolution three‐dimensional topographic maps of specific surface structures to address surface geologic processses. Results from the NLR investigation will contribute significantly to understanding the origin, structure, and evolution of Eros and other asteroidal bodies.
Photochemical mapping of Mars
Authors: Krasnopolsky Vladimir A.
Published: February 2004

The O2(1Δg) dayglow produced at 1.27 μm by ozone photolysis is ideal for ground‐based mapping of high‐altitude ozone using long‐slit high‐resolution spectrographs like CSHELL, CGS4, and Phoenix. Coupled to mapping H2O at 1.13 μm and CO and CO2 at 1.57 μm with the same instruments, it is possible to map hygropause using the rotational temperatures of CO2 and O2(1Δg). Strong seasonal variations of hygropause (from 10 to 40 km) and associated variations of high‐altitude ozone (by an order of magnitude above 20 km) are important novel concepts which may be studied in detail by these observations. Showing even greater promise is the combination of O2(1Δg) dayglow mapping with mapping of water abundance and temperature profiles by the thermal emission spectrometer onboard the Mars Global Surveyor. A list of problems which may be solved or improved upon by these observations is included.
High‐temperature life without photosynthesis as a model for Mars
Authors: Shock Everett L.
Published: February 2004

Discoveries in biology and developments in geochemistry over the past two decades have lead to a radical revision of concepts relating to the upper temperature at which life thrives, the genetic relationships among all life on Earth, links between organic and inorganic compounds in geologic processes, and the geochemical supply of metabolic energy. It is now apparent that given a source of geochemical energy, in the form of a mixture of compounds that is far from thermodynamic equilibrium, microorganisms can take advantage of the energy and thrive without the need for photosynthesis as a means of primary productivity. This means that life can exist in the subsurface of a planet such as Mars without necessarily exhibiting a surface expression. Theoretical calculations quantify the geochemically provided metabolic energy available to hyperthermophilic organisms in submarine hydrothermal systems on the Earth, and help to explain the enormous biological productivity of these systems. Efforts to place these models in the context of the early Earth reveal that substantial geochemical energy would have been available and that organic synthesis would have been thermodynamically favored as hydrothermal fluids mix with seawater.
Acidic volatiles and the Mars soil
Authors: Banin A. , Han F. X. , Kan I. , Cicelsky A.
Published: February 2004

Large portions of Mars' surface are covered with deposits of fine, homogeneous, weathered dusty‐soil material. Nanophase iron oxides, silicate mineraloids, and salts prevail in the soil. The mode of formation of this somewhat peculiar type of soil is still far from being clear. One scenario suggests that weathering took place during early epochs when Mars may have been “warm and wet”. The properties of the soil are not easily reconciled with this scenario. We propose another possible scenario that attributes, in part, the peculiar nature of the Martian dust and soil to a relatively “young” weathering product formed during the last few hundreds of millions of years in a process that involves acidic volatiles. We tested this hypothesis in an experimental study of the first step of acidolytic weathering of a partly palagonitized volcanic tephra of hawaiitic lava origin, using sulfuric, hydrochloric and nitric acids and their mixtures. The tephra effectively “neutralize” the added acidity. The protonic acidity added to the tephra attacks the primary minerals, releasing Fe, Al, and Mg, which control the pH, acting as Lewis‐acid species of varying acid strengths. The full amount of acidity added to the tephra is stored in it, but only a very small fraction is preserved as the original protonic acidity. The majority of the added sulfate and chloride were present as salts and easily solubilized minerals. Well‐crystallized sulfate salt minerals of aluminum and calcium were detected by powder X ray diffractometry, whereas secondary magnesium and iron minerals were not detected, due probably to lack of crystallinity. The presence of gypsum (CaSO4·2 H2O) and alunogen (Al2(SO4)3·17 H2O) is probably responsible for the observed increased hygroscopicity of the acidified tephra and their tendency to form hardened crusts. We suggest that if this mechanism is of importance on Mars, then the chemically weathered component of the Martian soil consists of a salt‐rich mineral mixture containing the salts of the anionicligands SO4 and Cl resulting from volatiles emitted from volcanoes during more recent eruptions (up to 109 years B.P.). The lack of liquid water on Mars surface during that time slowed or halted mineralogical evolution into highly crystallized minerals having large mineral grains. The chemically weathered components are mixed with the products of physical weathering. The recently formed soil may cover and coat more evolved, hydrothermally modified, mineral deposits formed in earlier epochs of Mars.
Clementine images of the lunar sample‐return stations: Refinement of FeO and TiO2 mapping techniques
Authors: Blewett David T. , Lucey Paul G. , Hawke B. Ray , Jolliff Bradley L.
Published: February 2004

Clementine UVVIS images of the lunar sample‐return sites have been processed and used to produce refined calibrations for the iron and titanium determination algorithms of Lucey et al. [1995, 1996]. The high spatial resolution of the Clementine data permits individual sampling stations to be resolved at the Apollo 15, 16, and 17 landing sites. We find an excellent, linear correlation between the spectral Fe and Ti parameters and the average FeO and TiO2 contents of soils sampled at each site or station. This correlation demonstrates that these techniques can confidently be applied to other areas of the Moon. The Luna 24 site does not fit the Ti relation found for other sites, suggesting that either its sample is nonrepresentative or the reported landing coordinates are incorrect.
An overview of the NEAR multispectral imager‐near‐infrared spectrometer investigation
Authors: Veverka J. , Bell J. F. , Thomas P. , Harch A. , Murchie S. , Hawkins S. E. , Warren J. W. , Darlington H. , Peacock K. , Chapman C. R. , McFadden L. A. , Malin M. C. , Robinson M. S.
Published: February 2004

The combined MSI‐NIS investigation on NEAR consists of a Multi‐Spectral Imager (MSI) and a Near‐Infrared Spectrometer (NIS). MSI covers the spectral range from 0.4 to 1.1 μm in seven narrow passbands and one broad filter. MSI has a field of view of 2.25° by 2.90° and will achieve an image scale of about 3 m/pixel at the surface of Eros. NIS covers the spectral interval from 0.8 to 2.6 μm: the range between 0.804 and 1.506 μm is measured by a 32‐element Germanium detector; a 32‐element Indium‐Gallium‐Arsenide detector observes wavelengths between 1.348 and 2.600 μm. The instrument has a selectable field of view of either 0.38°×0.76° or 0.76°×0.76°. A spatial resolution of about 300 m (100 times coarser than MSI) can be achieved at Eros. A major goal of the MSI‐NIS investigation is to determine the fundamental global properties of Eros, including spin state, size, and shape. Precise size and shape measurements are necessary to determine an accurate volume and thereby a mean density from mass measurements. MSI‐NIS spectral data will be combined with abundance determinations of key rock‐forming elements obtained by the X ray/gamma ray spectrometers (XGRS) to infer the distribution of minerals on Eros and constrain models of the asteroid's geochemical evolution. On approach to Eros, a search will be made for satellites: objects as small as 12 m (some 100 times smaller than Ida's Dactyl) could be detected.
Chemical zoning of olivine in several pallasites
Authors: Miyamoto M.
Published: February 2004

Chemical zoning profiles of olivines in the Esquel, Imilac, and Yamato 8451 pallasites were measured by using an electron probe microanalyzer in order to study their cooling histories. Pallasite olivines are considered to be compositionally uniform but show faint zoning for Fe‐Mg, CaO, Al2O3, Cr2O3, and MnO within a few hundred micrometers from the rim. The CaO, Al2O3, and Cr2O3 contents of olivines in pallasites decrease gradually toward the rim. The Fe‐Mg zoning and the MnO enrichment in olivine rims of pallasite olivines may reflect a redox process. On the basis of diffusion calculations to estimate the cooling rate by using chemical zoning of pallasite olivine, the formation process of chemical zoning was discussed. Similar cooling rates obtained for the Fe‐Mg, CaO, and MnO profiles of an olivine imply that these zoning patterns formed during the same event.
Determination of Martian meteorite lithologies and mineralogies using vibrational spectroscopy
Authors: Hamilton Victoria E. , Christensen Philip R. , McSween Harry Y.
Published: February 2004

We have acquired thermal infrared emission spectra of four Martian meteorite samples, ALH77005, Nakhla, Zagami, and EET79001, representing three major lithologies (Iherzolite, clinopyroxenite, and basalt). The spectra of these meteorites are significantly different from each other, and we can distinguish the three lithologies easily on the basis of their spectral morphologies. Using a linear deconvolution model, the modal mineralogies of ALH77005, Nakhla, and Zagami were derived from their spectra to within 2–19% of the modes derived by optical methods. For Zagami and EET79001, the correct mineral types were identified as present using the linear method, although an exact spectral match using available end‐member spectra was not obtained, probably due to the lack of a pigeonite end‐member spectrum or shock effects in the meteorites. The meteorite spectra we have acquired will be used for comparison with data to be returned by the thermal emission spectrometer (TES) on the Mars Global Surveyor orbiter and would also be useful for comparing to future rover‐ or lander‐based thermal IR spectra. Based on our results, comparisons of mineral end‐member and meteorite spectra with TES spectra of coarse regolith and rocky regions should aid identification and mapping of Martian surface lithologies and unit mineralogy.
The limits of life on Earth and searching for life on Mars
Authors: Nealson Kenneth H.
Published: February 2004

Considerations of basic properties of bacteria such as size, structure, and metabolic versatility allow one to understand how these remarkable life‐forms are so adaptable to environments previously thought to be uninhabitable. It is now appreciated that bacteria on Earth can utilize almost any redox couple that yields energy, taking advantage of this energy, while transforming the elements during metabolism. The ability to grow at the expense of inorganic redox couples allows the microbes to occupy niches not available to the more metabolically constrained eukaiyotes. Furthermore, the simplicity of the bacterial structure allows them considerably more resistance to environmental variables (pH, salinity, temperature) that are toxic or lethal to more complex organisms. This information can be used to explain the predominance of prokaryotes in extreme environments on Earth, and to speculate as to simple types of metabolism and biogeochemical cycles that may exist on this planet, Mars, and perhaps other non‐Earth environments.
Variations in Martian surface composition and cloud occurrence determined from thermal infrared spectroscopy: Analysis of Viking and Mariner 9 data
Authors: Christensen Philip R.
Published: February 2004

Viking infrared thermal mapper (IRTM) and Mariner 9 infrared interferometer spectrometer (IRIS) data were examined for evidence of spatial variations in the composition of surface materials and the abundance of atmospheric condensates. The IRTM instrument collected broadband spectral radiance in bands centered at 7, 9, 11, and 20 μm. These measurements were converted to emissivities at 9, 11, and 20 μm and used to construct multispectral images at five seasons (Ls 90–180°, 180–360°, 0–90°, 90–180°, and 180–360°) and at local times of 6–8, 8–10, 10–12, 12–14, and 14–16 H (24 H equals one Martian day). During dusty periods (Ls 180–360°), these images clearly revealed the presence of suspended dust. During clear periods (Ls 0–180°) the seasonal and diurnal variations in water‐ice cloud occurrence could be mapped using the 11 μm IRTM band. Clouds tended to occur over the Tharsis region and the region between 0 and 60°W near the equator, and to evolve from dispersed hazes to more localized hazes during the day. As northern summer progressed during the Viking period, the northern clouds transitioned from a diffuse haze to a more concentrated zone of clouds in the equatorial region with a well‐defined northern boundary. During clear periods the IRTM multispectral data reveal significant absorptions at 9, 11, and 20 μm that are strongly correlated with surface albedo. These absorptions are produced by surface materials, and individual four‐point spectra show compositional variations within both dark and bright material types. The IRIS instrument collected high‐spectral resolution (2.4 cm−1) data from 6 to 50 μm. Unfortunately, only ∼85 daytime spectra out of the ∼21,000 total collected were acquired after the intense global dust storm of 1971 subsided (after Ls 330°). The close agreement of these spectra, convolved to IRTM resolution, with the IRTM surface spectra confirms that they also represent surface, rather than atmospheric, materials. The IRTM four‐point spectra show similarities with plagioclase feldspar minerals, clays, and pyroxenes, although the low spectral resolution of IRTM prevents definitive mineral identification. Carbonates do not compose a significant fraction of the dark‐region materials. The IRIS surface spectra show similarities with feldspars, clays, and pyroxenes in the 8–12 μm region but do not match any of these minerals well in the 18–25 μm region. Overall, the IRTM and IRIS data are consistent with previous suggestions of mafic to ultramafic compositions, but data provide stronger evidence that unweathered plagioclase feldspars may be significant components of the present surface. Together, the IRTM and IRIS reveal the presence of absorption features associated with surface materials which should permit detailed surface compositional mapping using future thermal IR spectral measurements.
The lunar mascons revisited
Authors: Arkani‐Hamed Jafar
Published: February 2004

The entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high‐resolution Clementine data. The negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported. Both elastic support and viscous decay models are examined. For the elastic support models, the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential. An elastic layer thickness of about 50 km is required to support Imbrium, Serenitatis, and Nectaris mascons, about 35 km for Crisium mascon, and about 30 km for Smythii and Humorum mascons. A layer of about 20 km thickness can support Orientale mascon. The strength envelopes of the upper 100 km of the Moon within 4–3 Gyr ago show that the elastic layer was not thick enough to support the mascons in the early history. They decayed through viscous deformation of the lunar interior. A lower limit of 6×1024 Pa s is estimated for the lunar viscosity within 3.6–3 Gyr ago. We also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation. The crust beneath the mascon basins is about 30–40 km except for Crisium and Orientale, where the crust is about 20 km. The mare flows of about 3–6 km are obtained for almost all of the mascon basins. The topography and gravitational potential of Aitken basin shows that the basin is compensated at 52–54 km depth. The mantle beneath the basin has rebounded upward by about 20–30 km and is overlain by about 20–25 km of a mixture of the excavated crustal and mantle material. The lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation.
Mapping the FeO and TiO2 content of the lunar surface with multispectral imagery
Authors: Lucey Paul G. , Blewett David T. , Hawke B. Ray
Published: February 2004

The derivation of quantitative elemental concentrations from multispectral imaging of the Moon has long been a goal of lunar remote sensing. Concentration maps at the spatial resolutions available from the recent Clementine mission would provide a revolutionary new tool for understanding the origin and evolution of the lunar crust. Lucey et al. [1995] presented a method for extracting the concentration of Fe from multispectral imaging of the Moon. This paper examines and quantifies important aspects ofthat technique left unexamined by Lucey et al. which had the potential to severely limit its utility. These aspects include the effects of maturity, grain size, mineralogy, shading due to topography, and the presence of glass. We also present a new algorithm for derivation of TiO2 from multispectral imaging of both mare and highland units. We find that both techniques are only weakly sensitive to maturity and that they have about 1 wt % accuracy based on examination of the spectral properties and compositions of resolved lunar sampling stations presented by Blewett et al. [1997]. We also discuss these findings in the context of two contrasting views of the effect of composition on lunar spectral properties presented by Pieters and coworkers and Hapke and coworkers. We find the view of Hapke and coworkers to be more consistent with our observations. Using a global mosaic of Clementine multispectral data and these element derivation algorithms, we find that the global modal abundance of FeO is 4.5 wt %±1 wt % and the global modal abundance of TiO2 is 0.45 wt %±1 wt. %.