bluuebunny/crossref_metadata_2025 huggingface dataset:
Verification plan of ocean color and temperature scanner atmospheric correction and phytoplankton pigment by moored optical buoy system
Authors: Kishino Motoaki , Ishizaka Joji , Saitoh Sei‐ichi , Senga Yasuhiro , Utashima Masayoshi
Published: February 2004

A moored optical buoy system has been developed by the National Space Development Agency of Japan (NASDA) for verification of ocean‐observing remote sensing sensors of the Advanced Earth Observing Satellite (ADEOS). An underwater spectral radiometer was specifically designed for this optical system. The two upward radiance and downward irradiance correctors were connected with fiber optical system and were placed at the depth of 1.5 m and 6.5 m. The collector parts of the radiometer were extended from the center of the buoy system in order to avoid self shading with 3 m and 1.2 m arms at the depth of 1.5 m and 6.5 m, respectively. Spectral incident irradiance was measured at top of the buoy system. Phytoplankton pigment concentrations were monitored by Aquatracka‐III fluorometer placed at the bottom of the surface float. Atmospheric temperature, pressure, humidity, wind speed and direction, water temperature at a depth of 1.2 m and 6.5 m, and wave height and direction were also monitored. In this paper, we present results from test deployment during January 16 to March 15, 1995, in the Suruga Bay, off Shizuoka, Japan, and compare the water‐leaving radiance obtained by buoy with one observed by ship. The chlorophyll a concentrations calculated from water‐leaving radiance were also compared with chlorophyll fluorescence measured by fluorometer. It was proved that the self shading and wind affected the radiance and irradiance in the sea. It becomes clear that the quality check of the buoy data is very important for verification of the satellite data. We present also the verification plan of atmospheric correction and phytoplankton pigment for ADEOS/ocean color and temperature scanner (OCTS) using the sea truth data obtained from this buoy system and ships.
Stellar coronograph on the Come‐on‐Plus adaptive optics system: Description and preliminary results
Authors: Lagrange A.‐M. , Beuzit J.‐L. , Mouillet D.
Published: February 2004

We describe a coronograph built to work with the European Southern Observatory (ESO) adaptive optics system, which enables studies at IR wavelengths of the 1–7 arcsec environment of stellar objects, at high angular resolution (0.12 arcsec at 2.2 μ). We present preliminary results from the observation of two main sequence IR excess stars: HR 4796 and β Pictoris.
Search for extrasolar planets around radio‐emitting stars by very long baseline interferometry astrometry
Authors: Lestrade Jean‐François , Phillips Robert B. , Jones Dayton L. , Preston Robert A.
Published: February 2004

A planet orbiting a radio‐emitting star can be indirectly detected by high‐precision very long baseline interferometry (VLBI) astrometry through the reflex orbit of the star. We have observed the radio‐emitting star σ2 CrB at 15 epochs over 7.5 years by VLBI and fitted its five astrometric parameters to the measured VLBI coordinates. The postfit coordinate residuals have an rms scatter of 0.33 milliarcsecond (mas) when all 15 epochs are used. However, when only the seven epochs at which the star was in its radio quiescent regime are used, the postfit rms drops to 0.20 mas, indicating that the radio centroid is more stable than during outbursts. The systematic errors in these VLBI astrometric observations are estimated to be 0.1 mas only. The larger rms scatter found (0.20 mas) might be caused by either a random jitter of the radio source or a planetary perturbation that is not sampled sufficiently to be recognized by visual inspection of the postfit position residuals. This will be tested by more frequent VLBI observations of this star in the future. Finally, the theoretical (signal‐to‐noise ratio‐limited) astrometric precision of VLBI observations of radio‐emitting stars is ∼10 μarc sec and corresponds to an interesting limit to search for giant planets around stars up to 200 pc and even for an Earth‐like planet but around the nearest radio‐emitting star UV Ceti.
Applications of an energy transfer model to three problems in planetary regoliths: The solid‐state greenhouse, thermal beaming, and emittance spectra
Authors: Hapke Bruce
Published: February 2004

Several problems of interest in planetary infrared remote sensing are investigated using a new radiative‐conductive model of energy transfer in regoliths: the solid‐state greenhouse effect, thermal beaming, and reststrahlen spectra. The results of the analysis are as follows: (1) The solid‐state greenhouse effect is self‐limiting to a rise of a few tens of degrees in bodies of the outer solar system. (2) Non‐Lambertian directional emissivity can account for only about 20% of the observed thermal beaming factor. The remainder must have another cause, presumably surface roughness effects. (3) The maximum in a reststrahlen emissivity spectrum does not occur exactly at the Christiansen wavelength where, by definition, the real part of the refractive index equals one, but rather at the first transition minimum in reflectance associated with the transition from particle scattering being dominated by volume scattering to that dominated by strong surface scattering. The transparency feature is at the second transition minimum and does not require the presence of a second band at longer wavelength for its occurance. Subsurface temperature gradients have only a small effect on emissivity bands.
Thermal infrared observations of the condensing Martian polar caps: CO2 ice temperatures and radiative budget
Authors: Forget François , Pollack James B.
Published: February 2004

The physical processes that control the formation of the Martian seasonal polar caps are not completely understood. On the one hand, climate models reproducing the annual variations in atmospheric pressure caused by the condensation of the polar caps have shown that the amount of CO2 actually trapped in the polar regions in winter is lower than expected from simple energy balance considerations. On the other hand, the available spacecraft observations of the condensing polar caps are complex and puzzling. They are characterized by highly variable low‐emission zones exhibiting anomalously cold brightness temperatures. To better understand these results, we have carefully reanalyzed the Viking infrared thermal mapper (IRTM) measurements obtained during the polar night in both hemispheres. First, by removing the signature of the low‐emission zones in the data, we have retrieved the actual surface temperatures of the polar caps. We find that they were lower than the frost point of CO2 for the topography of the polar regions usually used in models, especially in the south polar region. However, our analysis reveals that the low‐emission zones were more frequent and more intense in the northern hemisphere. They strongly altered the polar radiative budget which is computed and analyzed here, and thus the CO2 condensation rate. We conclude that the models' tendency to overestimate the amount of CO2 ice condensing in the polar caps is explained by different causes in each hemisphere. In the north, the models did not simulate the low‐emission zones and underestimated the heat advected to the polar cap region during the dust storms, especially by the upper atmosphere polar warming. In the south, they overestimated the polar cap surface temperatures and also did not simulate the low‐emission zones.
Impact crater lakes on Mars
Authors: Newsom Horton E. , Brittelle Gregory E. , Hibbitts Charles A. , Crossey Laura J. , Kudo Albert M.
Published: February 2004

The robotic search for life on Mars centers on identifying accessible environments where the biological catalyst, water, has existed. The formation of large impact craters on Mars (>65 km diameter) may have resulted in the creation of ice‐covered impact crater lakes, which would not freeze for thousands of years, even under present climatic conditions. Water could be supplied from deep confined aquifers penetrated by the impact craters, without the need for surface melt water. Freezing of the lakes is postponed owing to heat from impact generated melt‐bearing deposits, from impact‐related uplift of hotter rocks from depth, and from the latent heat of freezing of a deep crater lake. Abundant morphologic evidence for ancient crater lakes has not been found in Viking images, except for craters associated with outflow channels. However ice‐covered crater lakes could have formed, and further searches for evidence of these lakes are warranted. The lake deposits from dissected impact craters may represent one of the best targets for future surface exobiology investigations or sample return missions from Mars.
Volcanic eruptions and intrusions on the asteroid 4 Vesta
Authors: Wilson Lionel , Keil Klaus
Published: February 2004

We use basic principles of fluid mechanics to explore the intrusive and eruptive consequences of early, large‐scale silicate melting within the asteroid 4 Vesta and relate our findings to the properties of the howardite‐eucrite‐diogenite meteorites. Surface lava flows on Vesta would commonly have had widths ranging from a few hundred meters to a few kilometers, and lengths lying between a few kilometers and at least several tens of kilometers. Flow thicknesses would have occupied a much narrower range, lying between about 5 and 20 m. These thicknesses imply cooling rates and plagioclase crystal growth rates which are extremely similar to those measured in the eucrite meteorites. Intrusions may have formed at very shallow depths, as cooling dikes failed to erupt their contents completely to the surface, or at the base of the crust, where rising magmas would have been neutrally buoyant as the density structure of Vesta's crust evolved. Deep intrusions would have had lateral extents up to 30 km and thicknesses up to 3 m; shallow intrusions would have had vertical extents less than 10 km and widths of ∼1 m. None of these intrusions and surface flows would have been thick enough or have formed frequently enough at a given location to have caused extensive thermal alteration of earlier eruptives, lending support to the idea that burial and subsequent long‐term exposure to the rising geothermal gradient was the main mechanism of thermal metamorphism.
Eclipses of Saturn's moons
Authors: Mallama Anthony , Krobusek Bruce
Published: February 2004

CCD photometric data for eclipses of Tethys, Dione, and Rhea are fit to model light curves that represent the geometry and radiometry of the events. Comparison of our midevent timings with modern ephemerides indicates that the predictions are typically accurate to about 300 km. We also present results from our model that allow eclipse and occultation photometry of Mimas through Phoebe to be used for precise astrometry of those satellites.
Shuttle imaging radar (SIR‐C/X‐SAR) reveals near‐surface properties of the South Patagonian Icefield
Authors: Forster Richard R. , Isacks Bryan L. , Das Sarah B.
Published: February 2004

Shuttle imaging radar C/X band synthetic aperture radar (SIR‐C/X‐SAR) views of the South Patagonian Icefield in southern Chile and Argentina demonstrate the ability of spaceborne multiparameter radar to detect climatically driven, intra‐annual changes in the snow and ice conditions on glaciers. The SIR‐C/X‐SAR system aboard space shuttle Endeavor acquired images during two 11‐day missions in April and October 1994. The radar signatures of differing snow and ice conditions are distinctive and homogeneous over large areas of the ice fields. The signatures are characterized mainly by (1) backscatter amplitude levels, (2) relative amplitudes of the C and L bands (wavelengths of 5.7 and 24 cm, respectively), and (3) polarization properties indicative of volumetric or surface scattering. The radar signatures are interpreted by correlating the radar characteristics with elevation of the snow and ice surfaces and with changes in the meteorological conditions. We are able to define four “radar glacier zones”: (zone A) a relatively dry snow zone with dominant C band returns; (zone B) a moderately wet snow zone with dominant L band returns; (zone C) a wet snow zone with weak returns in all bands; and (zone D) bare ice and/or heavily crevassed surfaces with strong returns in all bands. The spatial changes in the radar glacier zones between April and October are consistent with colder temperatures recorded in October, producing drier snow conditions at lower elevations than in April.
Detection of structural and lithological features underneath a vegetation canopy using SIR‐C/X‐SAR data in Zhao Qing test site of southern China
Authors: Guo Huadong , Zhu Liangpu , Shao Yun , Lu Xinqiao
Published: February 2004

In a subtropical region, the application of remote sensing in geological survey and mapping is limited by the dense vegetation and soil cover and poor data availability due to clouds and rain. This study emphasizes the detection of structural and lithological features underneath a vegetation canopy using shuttle imaging radar C/X band synthetic aperture radar (SIR‐C/X‐SAR) data. Zhao Qing test site in southern China was selected for this study. The SIR‐C/X‐SAR data have advantages including all weather, all time imaging capability, high altitude, and wide swath along with the expanded information from multifrequency and multipolarization that improves the geological interpretibility, especially in a moist, vegetated region. This paper presents interpretations of structures, beds, and lithostratigraphic units from the shuttle imaging radar data, and makes an assessment of SIR‐C/X‐SAR data for geological mapping.
Martian water vapor, 1988–1995
Authors: Sprague A. L. , Hunten D. M. , Hill R. E. , Rizk B. , Wells W. K.
Published: February 2004

We report new measurements of Martian atmospheric water vapor for the period 1991–1995 and discuss implications of these and earlier measurements from 1988 to 1989. Our measurements indicate abundances (precipitable micrometers (pr μm)) that show some departures from those of the Viking Mars atmospheric water detector (MAWD) experiment and other ground‐based measurement programs. Variation of water abundance within Martian season is sometimes as large as a factor of 3 from one year to the next. However, the seasonal shifts and variations between hemispheres show the same trends as observed by MAWD. Column abundances of water vapor varied from barely detectable, <1 (at Ls 320–340) to 36.4 pr μm (Ls 100) at high northern latitudes. Strong latitude variations were observed for all Ls seasons, with late spring and summers wet in both hemispheres. Northern latitudes are up to 5 times wetter than southern latitudes. Equatorial regions (30°S–30°N) show a rather stable abundance of atmospheric water varying between 2 and 20 pr μm, while much larger variations are observed at high latitudes. Southern atmospheric water drops below 10 pr μm rapidly in early autumn and is below our measurement threshold by late autumn. Strong diurnal variations show lowest water column abundance near the evening terminator.
Convection‐driven subsolidus crustal thickening on Venus
Authors: Kidder Jennifer G. , Phillips Roger J.
Published: February 2004

We analyze the phenomenon of subsolidus crustal flow in response to mantle convection and test the hypothesis that Venusian crustal plateaus such as Ovda Regio formed over mantle downwellings. We investigate this process using results from the parameterized convection models of Solomatov and Moresi [1996] to calculate stress boundary conditions for the finite element code TECTON. The effects of a brittle crust are simulated by constraining the minimum crustal strain rates in the models with a diabase strength envelope. A series of models that could correspond to Venus ∼1 Gyr ago were created by varying such parameters as the crustal and mantle flow laws, plastic behavior of the upper crust, crustal thermal conductivity, and the temperature at the planet's surface (possibly higher due to increased interior outgassing). As expected, crustal thickening was found to be negligible in a stagnant lid regime, regardless of crustal rheology. In a small viscosity contrast regime, plateaus greater than 1 km in elevation are possible within the lifetime of a mantle downwelling only for a weak crustal flow law. Therefore it is unlikely that Venusian crustal plateaus such as Ovda Regio formed as a result of subsolidus crustal thickening over downwellings unless the crust had considerably less strength than indicated by the dry diabase measurements of Mackwell et al. [1995, 1996].
Oxygen extraction from lunar soils and pyroclastic glass
Authors: Allen Carlton C. , Morris Richard V. , McKay David S.
Published: February 2004

We have conducted experiments on 16 lunar soils and three lunar pyroclastic glass samples to study the extraction of oxygen, an important resource for a future lunar base. The samples were chosen to span the range of composition, mineralogy, and maturity represented in the Apollo sample collection. Each sample was reduced in flowing hydrogen for 3 hours at 1050°C. The dominant effect was reduction of Fe2+ (as FeO) in minerals and glass to iron metal, with concomitant release of oxygen. Oxygen extraction was strongly correlated with initial Fe2+ abundance. The data and supporting experiments also indicate extraction of oxygen from TiO2 and SiO2. No dependence of oxygen release on sample maturity could be identified. Oxygen was extracted, in decreasing order of efficiency, from ilmenite, agglutinitic and pyroclastic glass, olivine, and pyroxene. The experimental reduction of lunar soil provides a method for assessing the oxygen production potential for sites on the lunar surface from lunar orbit. Our results show that oxygen yield from the regolith can be predicted from knowledge of only one parameter, total iron content. This parameter can be measured from orbit by gamma ray spectrometry or multispectral imaging. These experimental data also support the selection of feedstocks and operating parameters for a lunar oxygen plant.
A reappraisal of the Martian 36Ar/38Ar ratio
Authors: Bogard Donald D.
Published: February 2004

The currently used value of 4.1±0.2 for the 36A/38Ar isotopic ratio in the Martian atmosphere is reappraised, and a significantly lower ratio is suggested. Previous analyses of noble gases in impact glass from some Martian meteorites demonstrate that large quantities of Martian atmospheric gases were shock‐emplaced into these samples. However, several observations indicate that this trapped Martian gas is composed of two components, one atmospheric and one probably from the Martian mantle. These observations include large variations in 36Ar/38Ar during stepwise gas release, variations in the Ar/Kr/Xe elemental ratios among Martian meteorites, and variations in the cosmogenic‐corrected, trapped 36Ar/38Ar ratios over 3.5–4.3 among shock glass samples. Uncertainties in applied corrections for cosmogenic Ar cannot explain these variations. By assuming a range of reasonable values for Martian atmospheric and mantle 40Ar/36Ar, the observed 40Ar/36Ar ratios in shock glass are used to correct for the mantle component and to derive a more precise ratio for the atmospheric component. Using this procedure, one obtains an upper limit for Martian atmospheric 36Ar/38Ar of 3.9, and a probable, but poorly defined range for Martian atmospheric 36Ar/38Ar of ∼3.0–3.6. These lower ratios imply that the degree of mass fractionation during Ar loss from Mars' upper atmosphere is considerably larger than that previously calculated.
Rocks and aeolian features in the Mars Pathfinder landing site region: Viking infrared thermal mapper observations
Authors: Edgett Kenneth S. , Christensen Philip R.
Published: February 2004

Albedo, rock abundance, and thermal inertia derived from Viking infrared thermal mapper observations provide information about the surface materials within the Mars Pathfinder landing ellipse in Ares Vallis. Relative to the rest of Mars, the site has an intermediate albedo (0.19–0.23), intermediate‐to‐high bulk thermal inertia (410–540 J m−2 s−0.5 K−1), and high rock abundance (18–25%). At local scales the actual surface distribution of rocks might be heterogeneous, as on terrestrial catastrophic flood surfaces, where rocks tend to be concentrated on fluvially armored surfaces and/or bars. Albedo increases and thermal inertia decreases from the northeast to the southwest in the ellipse, owing to (interpreted) windblown dark sand from Acidalia Planitia. If Mars Pathfinder lands at the southwest end of the landing ellipse, the scene is likely to be the most similar to that of the Viking 1 lander; while a landing at the northeast end of the ellipse is most likely to provide a view that is different from the Viking sites because of low‐albedo material. A landing at the center of the ellipse might put the spacecraft near one of two crater clusters that are interpreted to have dark sandy material in or on their ejecta. Aeolian activity during the 30‐day Primary Mission might be limited because it is mid‐northern summer, a time in which no historic dust storms have been seen in the region, and a season when regional winds should be weak relative to other times during the year.
A coupled thermal‐mechanical model for corona formation on Venus
Authors: Musser George S. , Squyres Steven W.
Published: February 2004

We develop a model of the combined thermal and mechanical evolution of diapirs in the mantle of Venus. The diapir is treated as an oblate spheroid rising through a viscous fluid and ultimately impinging on a rigid overlaying “lid”. Drag forces imposed by the lid cause the diapir to spread and flatten as it rises. We parameterize the heat loss from the rising diapir using a Nusselt number formulation and treat the resulting loss in buoyancy in our flow calculation. The model predicts the evolution timescale and degree of flattening of a diapir as it rises, as well as the stresses exerted on the underside of the lithosphere. In order to explore diapir behavior further, we check our analytical model against the predictions of the finite element code MANTLE. From the combined results of these models and observations of Venusian coronae, we are able to make a number of inferences about Venusian diapirism and mantle properties. We find that the diapirs responsible for formation of Venusian coronae have an initial size distribution extending from about 30 to 100 km in radius. Typical evolution timescales for these diapirs are 30–50 Myr. If Venus' global average resurfacing age is 300–500 Myr, then our results are consistent with a rate of diapirism that has been roughly constant over this period, and with an effective mantle viscosity of 1021 Pa s.
Thermal conductivity measurements of particulate materials 2. Results
Authors: Presley Marsha A. , Christensen Philip R.
Published: February 2004

A line‐heat source apparatus was assembled for the purpose of measuring thermal conductivities of particulate samples under low pressures of a carbon dioxide atmosphere. The primary result of this project is the compilation of the first comprehensive suite of measurements of the dependence of thermal conductivity on particle size. The thermal conductivity increases with increasing particle size and atmospheric pressure. In particular, over the range of Martian atmospheric pressures, from 1 to 7 torr, the thermal conductivity was found to be empirically related to approximately the square root of the particle diameter and the square of the cubed root of the atmospheric pressure. At the average pressure of the Martian surface (6 torr) the thermal conductivity varies from 0.011 W/m K, for particles less than 11 μm in diameter, to 0.11 W/m K, for particles 900 μm in diameter. These results differ significantly from the particle size dependence estimated for Mars from previous measurements, except for 200‐μm particles, whose thermal conductivity is 0.053 W/m K. The thermal conductivities of larger particles are lower than the previous estimate, by 40% at 900 μm, and the thermal conductivities of smaller particles are higher than the previous estimate, by 60% at 11 μm. These newer estimates agree with other lines of evidence from Martian atmospheric and surficial processes and lead to improved particle size estimates for most of the planet's surface.
Mars Pathfinder landing site assessment with Goldstone delay‐Doppler and CW radar experiments
Authors: Haldemann A. F. C. , Mitchell D. L. , Jurgens R. F. , Slade M. A. , Muhleman D. O.
Published: February 2004

We present the results of 3.5‐cm delay‐Doppler and Doppler‐only (continuous wave or CW) radar experiments to assess three potential Mars Pathfinder landing sites: Ares Vallis, Tritonis Lacus, and northwest (NW) Isidis. The regional relief at all of the landing sites is appropriate for a Pathfinder landing sequence: east‐west slopes do not exceed 3° at any of the sites. We find that Ares Vallis has a Hagfors rms slope of θrms=4.8°±1.1° as measured by delay‐Doppler radar, and θrms=6.4°±0.6° measured by CW radar. These values are similar to, or less than the previous measurements of the Viking Lander 1 region. The Tritonis Lacus landing site is rougher with delay‐Doppler, θrms=5.6°±0.6°, while the NW Isidis landing site is very smooth, both in a regional sense (slopes <0.7°) and in a Hagfors rms slope sense: θrms=1.8°±0.2°. Reflectivities at all of the sites should be sufficient to allow the radar altimeter on Pathfinder to function properly.
The interior structure of Mars: Implications from SNC meteorites
Authors: Sohl Frank , Spohn Tilman
Published: February 2004

Two end‐member models of Mars' present interior structure are presented: the first model is optimized to satisfy the geochemical data derived from the SNC meteorites in terms of the bulk chondritic ratio Fe/Si=1.71, while the second model is optimized to satisfy the most probable maximum value C=0.366×Mprp2 of the polar moment of inertia factor. Hydrostatic equilibrium and stationary heat transfer are assumed, and the basic differential equations for the mechanical and thermal structure are solved numerically together with an isothermal Murnaghan‐Birch type equation of state truncated in Eulerian strain at forth order. We obtain the radial distribution of mass, hydrostatic pressure, gravity, temperature, and heat flow density along with the corresponding density stratification, viscosity profiles, and the global seismic velocity structure of model Mars. The first model being consistent with the geochemical requirement produces C=0.357×Mprp2, whereas the second model commensurate with the geophysical constraint gives Fe/Si=1.35. The calculated central pressure is about 40 GPa in both models, and the central temperature is in the 2000 to 2200 K range. The model calculations suggest a Fe‐Ni‐FeS core a little less than one half of the planetary radius in size surrounded by a silicate mantle subdivided into lower spinel and upper olivine layers and overlain by a 100‐ to 250‐km thick basaltic crust and a surface heatflow density of 25 to 30 mW m−2. In both models the pressure in the mantle is not sufficient for the spinel to perovskite transition to occur. The present thermal lithosphere is estimated to be about 500 km thick and to be subdivided into a 300‐km‐thick outermost rheological lithosphere and an underlying thermal boundary layer of mantle convection. Given the core sulfur content of 14 wt% as derived from SNC meteorites, the Martian core is found to be entirely molten, implying the nonoperation of a self‐sustained dynamo due to the absence of sufficiently vigorous convection.
Geotraverse from Xanthe Terra to Chryse Planitia: Viking 1 Lander region, Mars
Authors: Crumpler L. S.
Published: February 2004

High‐resolution (1:500,000‐scale) geologic mapping of a 300‐km‐wide and 1500‐km‐long strip, or geotraverse, across the transition from the Xanthe Terra cratered highlands to the Chryse Planitia lowlands encompasses an area on the margin of the Chryse Basin unaffected by outflow channels. It thus characterizes the transition where it has been relatively unmodified by erosion and the stratigraphy of pre‐outflow units is well‐preserved. Two types of highland‐lowland boundary are identified: (1) a topographic boundary and (2) a geologic/morphologic boundary. The topographic boundary occurs well within the cratered highlands and separates a lower‐standing surface with characteristics transitional to cratered highlands from the true highland surface of Xanthe Terra. The lower transitional highland surface, or transition zone, is partially inundated by plains‐forming materials, interpreted to be plains type lava flows of late Noachian‐early Hesperian age similar to later basin‐fill material forming Hesperian‐aged lowland ridged plains. The geologic boundary between this transitional surface and ridged lowland plains surface is identified with the traditional highland‐lowland boundary as mapped in previous studies. Mapping in this study identifies a moat‐like region between this geologic boundary and the basin interior is filled with an easily eroded material. Erosion of the moat‐filling deposit along the outer margins of the Chryse basin accounts for the streamlined tables formed during outflow channeling throughout the margins of Chryse Planitia. The geology of the central basin interior, where the Viking 1 Lander is located, is consistent with the presence of fluvial sediments derived from both the adjacent highlands and remobilized from the marginal moat‐filling unit, and deposited near the termini of the Maja and Kasei Valles outflow channels. Because the plains‐forming lavas overlie much of the proximal portions of the highlands and moat‐filling sediments ring the margins of the basin, materials eroded from the transition zone and deposited toward the basin interior by later outflow channels may be similar to interior plains lavas and marginal moat‐filling deposits. If the transitional highland surface is typical of the basin elsewhere, true highland rocks are likely to be a small component of any outflow channel sediments, even in settings near the basin margin. Rock populations and sediments at the proposed Mars Pathfinder site, located near the geologic boundary further east, could contain a significant portion of materials typical of lowlands in addition to some highland materials.
The imager for Mars Pathfinder experiment
Authors: Smith P. H. , Tomasko M. G. , Britt D. , Crowe D. G. , Reid R. , Keller H. U. , Thomas N. , Gliem F. , Rueffer P. , Sullivan R. , Greeley R. , Knudsen J. M. , Madsen M. B. , Gunnlaugsson H. P. , Hviid S. F. , Goetz W. , Soderblom L. A. , Gaddis L. , Kirk R.
Published: February 2004

The imager for Mars Pathfinder (IMP), a stereoscopic, multispectral camera, is described in terms of its capabilities for studying the Martian environment. The camera's two eyes, separated by 15.0 cm, provide the camera with range‐finding ability. Each eye illuminates half of a single CCD detector with a field of view of 14.4×14.0° and has 12 selectable filters. The ƒ/18 optics have a large depth of field, and no focussing mechanism is required; a mechanical shutter is avoided by using the frame transfer capability of the 512×512 CCD. The resolving power of the camera, 0.98 mrad/pixel, is approximately the same as the Viking Lander cameras; however, the signal‐to‐noise ratio for IMP greatly exceeds Viking, approaching 350. This feature along with the stable calibration of the filters between 440 and 1000 nm distinguishes IMP from Viking. Specially designed targets are positioned on the Lander; they provide information on the magnetic properties of wind‐blown dust, measure the wind vectors, and provide radiometric standard reflectors for calibration. Also, eight low‐transmission filters are included for imaging the Sun directly at multiple wavelengths, giving IMP the ability to measure dust opacity and potentially the water vapor content. Several experiments beyond the requisite color panorama are described in detail: contour mapping of the local terrain, multispectral imaging of the surrounding rock and soil to study local mineralogy, viewing of three wind socks, measuring atmospheric opacity and water vapor content, and estimating the magnetic properties of wind‐blown dust. This paper is intended to serve as a guide to understanding the scientific integrity of the IMP data that will be returned from Mars starting on July 4, 1997.
High‐resolution spectroscopy of Mars at 3.7 and 8 μm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO
Authors: Krasnopolsky V. A. , Bjoraker G. L. , Mumma M. J. , Jennings D. E.
Published: February 2004

We report the first sensitive upper limits for H2O2, H2CO, and HCl, a sensitive upper limit for CH4, and a measured column abundance for HDO. A combination of the Kitt Peak National Observatory (KPNO) 4‐m telescope and Fourier transform spectrometer with the Goddard Space Flight Center (GSFC) postdisperser was used to observe low‐latitude regions of Mars in spectral ranges of 2650–2800 cm−1 and 1229–1237 cm−1 with resolving power v/δv=2.7×105 and 1.2×105, respectively. The main spectral features are lines of isotopic CO2 and HDO. A radiation transfer code has been developed which divides the atmosphere into 30 layers and the Voigt profile of each line in each layer into 60 intervals. This code couples the reflected solar and thermal radiations. A search for H2O2 at 1229–1237 cm−1 results in a 2‐σ upper limit of 30 ppb, close to the predictions of recent photochemical models. Our 2‐σ upper limit for HCl (<2 ppb) precludes any significant chlorine chemistry in the atmosphere. Our value for methane (70±50 ppb) is consistent with, but does not improve upon, earlier results from Mariner 9 infrared interferometer spectrometer (IRIS). Our 2‐σ upper limit for H2CO (3 ppb) is much smaller than recently claimed abundances. The observed HDO lines result in an abundance of (6.06±0.5)×1016 cm−2, which, when compared with that of H2O measured by the Viking orbiters at the same season and latitudes, yields an enrichment in the D/H ratio of a factor of 5.5±2 relative to Earth. The given uncertainty is mainly caused by possible variations of Mars' atmospheric water abundance.
Impact of a paleomagnetic field on sputtering loss of Martian atmospheric argon and neon
Authors: Hutchins Kevin S. , Jakosky Bruce M. , Luhmann Janet G.
Published: February 2004

We examine the implications of including a paleomagnetic field on sputtering loss of argon and neon from the Martian atmosphere. In a previous investigation [Hutchins and Jakosky, 1996], we found that collisional sputtering from the exobase by oxygen pickup ions dramatically modified the evolution of atmospheric argon and neon (removing greater than 85% of outgassed 36Ar over time and the present atmospheric allotment of 20Ne in <100 Myr) and could easily reproduce the anomalous isotopic fractionation of 36Ar/38Ar. However, the existence of an intrinsic magnetic field could limit sputtering loss by deflecting the solar wind around the upper atmosphere, reducing the number of oxygen pickup ions produced. Evaluation of argon and neon atmospheric evolution including a magnetic field results in lower sputtering loss rates if the magnetic field shut off between 2.5 and 3.6 Gyr. Nonetheless, the extent of sputtering loss requires atmospheric input from sources, in addition to outgassing by intrusive and extrusive volcanism, capable of providing 4–100 times more argon and 40–1800 times more neon (than provided by volcanic outgassing), dependent on the time that sputtering begins. The additional volatile source(s) must also preferentially outgas neon relative to argon by a factor of between 10 and 26.
Momentum balance of the Venusian midlatitude mesosphere
Authors: Imamura Takeshi
Published: February 2004

The downward control principle is applied to estimate the vertically integrated zonal force driving the midlatitude lower mesosphere on Venus. The distinct localization of the forcing in the midlatitude implies two candidates for the momentum carrier: Rossby wave; and internal gravity waves generated by shear instability. Rough estimates of the Eliassen‐Palm (EP) flux suggest that the meridional circulation will be driven principally by the EP flux divergence associated with a Rossby wave, although the contribution of gravity waves cannot be ruled out. It is also shown that advective transport is as important as eddy diffusion for tracer transport.
Low‐temperature reflectivity spectra of red hematite and the color of Mars
Authors: Morris Richard V. , Golden D. C. , Bell James F.
Published: February 2004

Reflectivity spectra (visible and near IR) were measured near 141, 210, and 300 K for four red and well‐crystalline powders of hematite (red hematite) used as commercial pigments, two samples of volcanic tephra from Mauna Kea volcano that contain red hematite as their dominant pigment, three samples of palagonitic tephra from the same location that contain nanophase ferric oxide as their dominant pigment, and two mixtures of the two types of pigmenting phases. Relative proportions of red hematite and nanophase ferric oxide were determined by Mössbauer spectroscopy. For samples containing red hematite as the dominant pigment, the positions of the ferric electronic transitions near 430, 500, 630, and 860 nm are essentially independent of temperature, but their widths decrease with decreasing temperature. This decrease results in a well‐defined minimum for the band at 630 nm at low temperatures and in significant increases in reflectivity in spectral regions near 1050 and 600 nm. For example, the reflectivity ratios R600/R530 and R600/R860 both increase by a factor as large as ∼1.4 between 300 and 140 K. The spectral features from nanophase ferric oxide in samples of palagonitic tephra are nearly independent of temperature. Spectral data of Martian bright regions that are characterized by a shallow band minimum near 860 nm, a reflectivity maximum near 740 nm, a distinct bend near 600 nm, and a shallow absorption edge from ∼400 to 740 nm are attributed to the presence of nanophase ferric oxide plus subordinate amounts of red hematite. The 600‐, 740‐, and 860‐nm features are associated with red hematite. Because the reflectivity of red hematite at 600 nm is strongly dependent on temperature and because this wavelength is in the red part of the visible spectrum, the color of the Martian surface may vary as a function of its temperature. A conservative upper limit for the red hematite content of the optical surface of Mars is 5%.
High‐resolution (104 years) deep‐sea foraminiferal stable isotope records of the Eocene‐Oligocene climate transition
Authors: Zachos James C. , Quinn Terrence M. , Salamy Karen A.
Published: February 2004

We have constructed high‐resolution (104– 105 years) benthic foraminiferal δ13C and δ18O records for the upper Eocene through lower Oligocene of two pelagic sequences, Deep Sea Drilling Project (DSDP) Site 522 in the Angola Basin, South Atlantic Ocean, and Ocean Drilling Program (ODP) Site 744 in the southern Indian Ocean. These records provide improved constraints on both the timing and magnitude of marine oxygen and carbon isotope events from 30 to 35 Ma. The oxygen isotope records indicate that the ubiquitous δ18O increase (Oi‐1), which marks the rapid expansion of continental ice sheets and a minimum of 3° to 4°C of cooling of bottom waters in the earliest Oligocene (33.6 Ma), occurred in <350 kyr. More than half the transition occurred over the final 40–50 kyr. This period of lower temperatures and widespread continental glaciation persisted for roughly 400 kyr (i.e., the duration of magnetochron C13n). These records also indicate that this interval was characterized by at least two ∼ 100‐kyr waxing and waning cycles (Oi‐1a and Oi‐1b) and possibly several higher‐frequency events. The benthic foraminiferal δ13C records show a positive 0.8‰ excursion that is nearly isochronous with the Oi‐1 oxygen isotope increase. Similar magnitude δ13C increases at other sites indicate this was a global phenomenon suggestive of an unusually large perturbation to the carbon cycle. This excursion was followed by smaller amplitude δ13C oscillations with periods of roughly ∼400 kyr. We suspect that the ubiquitous Oi‐1 δ13C excursion resulted from a brief but substantial increase in export production and carbon burial.
Aptian‐Albian sea level history from Guyots in the western Pacific
Authors: Röhl Ursula , Ogg James G.
Published: February 2004

Relative sea level fluctuations are an important control on patterns of sedimentation on continental margins and provide a valuable tool for regional correlations. One of the main objectives of combined Ocean Drilling Program Legs 143 and 144 was drilling the thick carbonate caps of a suite of seamounts, called guyots, scattered over the northwestern Pacific. The array of drowned Cretaceous banks includes four carbonate banks of Aptian‐Albian age. These particular carbonate banks display emergent surfaces if regional sea level falls faster than the rate of guyot subsidence, or intervals of condensed parasequences and well‐cemented peritidal crypto‐algal flats if the rate of sea level fall is slightly less than guyot subsidence. Rapid rises of sea level following these sequence boundaries are recorded as drowning of the emergent horizons or as pronounced deepening of facies. The cored lithologies and downhole geophysical and geochemical logs were used to identify depositional sequences and surfaces of exceptional shallowing or deepening. A combination of biostratigraphic datums, carbon and strontium isotope curves, relative magnitude of surfaces of emergence, relative thicknesses of depositional sequences, sea level events, and counts of upward shallowing cycles or parasequences were used to correlate sequences among the four sites. After compensating for thermal subsidence rates at each guyot, an identical pattern of major Aptian‐Albian eustatic sea level events is evident throughout this large portion of the Pacific Ocean. There are approximately 12 Aptian and 12 Albian significant sequence boundaries, of which a third were associated with major episodes of emergence. When these events are compared with Aptian‐Albian relative sea level changes observed in European shelf successions, the major sequence boundaries and transgressive surges can be easily correlated, and it appears that both regions also display the same number of minor events. Therefore we can apply the relative timing of these events from the thermal subsidence rates and parasequence counts of the Pacific banks to construct an improved scaling of the associated ammonite zones and biostratigraphic datums in the Aptian‐Albian interval.

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Rapid changes in surface and deep water conditions at the Faeroe Margin during the last 58,000 years
Authors: Rasmussen Tine L. , Thomsen Erik , van Weering Tjeerd C. E. , Labeyrie Laurent
Published: February 2004

A high‐resolution piston core, ENAM93‐21, from a water depth of 1020 m near the Faeroe‐Shetland Channel is investigated for variations in magnetic susceptibility, surface oxygen isotopes, grain size distribution, content of ice‐rafted detritus (IRD), and distribution of planktonic and benthic foraminifera. The core, covering the last 58,000 years, is correlated with the Greenland ice cores and compared with paleorecords from the Norwegian Sea and the North Atlantic Ocean. All fifteen Dansgaard‐Oeschger climatic cycles recognized from the investigated time period in the Greenland ice cores have been identified in the ENAM93‐21 core. Each cycle is subdivided into three intervals on the basis of characteristic benthic and planktonic faunas. Interstadial intervals contain a relatively warm planktonic fauna and a benthic fauna similar to the modern fauna in the Norwegian Sea. This indicates thermohaline convection as at present, with a significant contribution of deep water to the North Atlantic Deep Water (NADW). Transitional cooling intervals are characterized by more cold water planktonic foraminfera and ice‐related benthic species. The benthic fauna signifies restricted bottom water conditions and a reduced contribution to the NADW. The peak abundance of N. pachyderma (s.) and the coldest surface water conditions are found in the stadial intervals. The benthic fauna is dominated by species with an association to Atlantic Intermediate Water, suggesting an increased Atlantic influence in the Norwegian Sea, and there was probably no contribution to the NADW through the Faeroe‐Shetland Channel. The three different modes of circulation can be correlated to paleoceanographic events in the Norwegian Sea and the North Atlantic Ocean.
Rapid changes in ocean circulation and atmospheric radiocarbon
Authors: Stocker Thomas F. , Wright Daniel G.
Published: February 2004

A latitude‐depth, coupled global ocean‐ice‐atmosphere model is extended to include a simple biosphere component. A physically reasonable adjustment of runoff into the North Atlantic is invoked to achieve a transient response to glacial meltwater perturbations, which closely resembles the Younger Dryas climate event. We then investigate the evolution of the isotopic ratio of atmospheric radiocarbon, Δ14C, due to the rapid changes of deep ocean circulation. When the North Atlantic branch of the conveyor belt circulation is interrupted, the oceanic uptake of radiocarbon is reduced, resulting in an increase of atmospheric Δ14C by about 35 ‰. The reduction of ventilation in the North Atlantic is partly compensated by an increase of the 14C ratios of the biosphere, the Southern Ocean, and the upper ocean above 1000 m depth. A plateau of the 14C year/calendar year relation can be generated at the time of the rapid reinitiation of deep ocean ventilation which begins coincident with the major temperature increase and lasts for about 60 years. It is hence significantly shorter than that found by analyzing tree rings during the termination of Younger Dryas (longer than 400 years). A sensitivity study reveals that the duration of the plateau depends strongly on the transient evolution of the gas exchange rate and can increase to 150–300 years if changes of pCO2 or sea ice coverage are taken into account.