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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Io's surface composition based on reflectance spectra of sulfur/salt mixtures and proton-irradiation experiments

Available full-disk reflectance spectra of Io in the range 0.3 to 2.5 microns have been used to determine a surface compositional model for Io that is consistent with Io's other known chemical and physical properties. Results indicate that the surface of Io contains abundant dehydrated salts of high Na, Mg, and Fe(3+) content such as bloedite and ferrous iron sulfate. Experiments were performed studying the irradiation damage effects from low-energy proton bombardment, since Io is immersed in Jupiter's magnetosphere.

Nash, D. B.↗
NASA NTRS1977

Io's surface composition - Observational constraints and theoretical considerations

Observations of line emission from neutral and ionic species in the Io-surrounding cloud, reflectance studies and theoretical considerations suggest Io's surface is unlike that of any other body in the solar system. The cloud has a peculiar composition which we show is probably not due to cloud/surface fractionation. Io's surface may be largely covered with an endogenically produced mixture of S and dehydrated salts, or by accretion-fractionated compounds modified by charge particle bombardment.

Fanale, F. P.↗
NASA NTRS1982

Io's surface - Its phase composition and influence on Io's atmosphere and Jupiter's magnetosphere

The evidence and interpretations pertaining to the surface phase composition of Io and the mechanisms by which Io's surface influences its atmosphere are discussed. The mechanism by which Io's surface and/or atmosphere supplies neutral and ionic species to the region around the satellite and ultimately to the Jovian magnetosphere is also discussed. A model is suggested in which the global SO2 gas abundance is primarily controlled by buffering in the brightest, coldest regions. The net SO2 flux across the disk is limited by regional cold trapping on high albedo regions and possibly by the resistance of a tenuous non-SO2 residual atmosphere. The continuing migration of SO2 toward cooler regions and those lacking SO2 sources is opposed by SO2 destruction and planetary ejection processes, including sputtering, thus preventing buildup of thick, ubiquitous SO2 coverage.

Fanale, F. P.↗
NASA NTRS1974

On the surface composition of Io

The wavelength dependence of the reflectivity of Io indicates the presence of two materials on the surface of this satellite of Jupiter. These materials are sulfur and an unspecified material (R1) which shows a wavelength dependence of its reflectivity for wavelengths from 0.3 to 1.0 micron similar to the non-H2O frost spectrum of the rings of Saturn. A 60/40 admixture of these two spectra matches the observed reflection spectrum of Io from 0.3 to 3.0 microns, if the spectrum of R1 is featureless for wavelengths above 1 micron. Sulfur will give rise to a posteclipse brightening. The variation with wavelength of the temperature dependence of the reflectivity of sulfur will allow an observational confirmation of the presence of sulfur on Io. The material R1 should show a large geometrical albedo. The translucency of sulfur is consistent with the polarization-phase curve of Io. The material R1 is also required to be translucent.

Wamsteker, W.↗
NASA NTRS1974

Io - A surface evaporite deposit

A model is suggested for Io's surface composition involving evaporite salt deposits, rich in sodium and sulfur. According to this model, these deposits were produced as a result of the migration of salt-saturated aqueous solutions to Io's surface from a warm or hot interior followed by loss of the water to space. This model satisfies cosmochemical constraints based on Io's initial composition, current density, and thermal history. Salt-rich assemblages are easily derivable from the leaching of carbonaceous chondritic material. The chemical and optical properties of such deposits, after modification by irradiation, can be used to explain Io's overall albedo and spectral reflectance, its dark reddish poles, and the observed sodium emission as well as or better than other currently suggested materials.

Fanale, F. P.↗
NASA NTRS1985

Photometric Analysis of Jupiter-illuminated Images of Io

Several sequences of the dark (Jupiter-illuminated) side of Io obtained during the Voyager 2 encounter present opporunity for understanding several problems relating to the surface composition of Io. The existence or absence of SO2 condensates on the night side is a sensitive indicator of an SO2 atmosphere. Preliminary analysis of the night side Io images suggests localized brightenings of approximately 25% may exist. Examination of the night side images represents an even more sensitive indicator for pure sulfur. Between 60 and 130 degrees (the minimum nighttime and maximum daytime temperatures, respectively), the relative spectral reflectance for yellow sulfur observed in the Voyager green and clear filters decreases by 25%. This decrease should be detectable on the nightside images. A search of the Voyager 2 Jupiter-illuminated images yielded a single pair of green and clear images. In these images one hemisphere of Io is Sun-illuminated and the other is Jupiter illuminated. Geologically similar regions of Io are being selected to obtain average color ratios of specific geologic units for both day and night sides.

Buratti, B. J.↗
NASA NTRS1980

Visible spectral reflectance measurements /0.33-1.1 microns/ of the Galilean satellites at many orbital phase angles

One hundred eighty-seven reflectance spectra (0.33-1.10 microns) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6 deg. Solar phase angle coefficients beyond 0.55 micron are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 micron observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambiguously attribute this particular decrease in reflectance to a change in Io's surface composition.

Mcfadden, L. A.↗
NASA NTRS2000

New Results on Io's Color and Composition

Galileo's recent high-resolution imaging provides new insights into the nature of Io's colorful surface, shedding light on the composition and origin of pyroclastic deposits and suggesting that Io's mysterious green spots are due to coating or alteration of silicate lavas.

Geissler, P.↗
NASA NTRS2002

The Diverse Surface Compositions of the Galilean Satellites

The galilean satellites represent a diverse collection, ranging from the volcanic moon Io, with a surface that is changing yearly, to Callisto, with a dark, ancient surface overlying ice. The composition of these surfaces are also quite different due to a variety of processes and influences, including tidal heating, radiolysis, gardening, a magnetic field (Ganymede), and meteoritic infall. Io's surface contains large quantities of sulfur dioxide (SO2) and colorful sulfur allotropes, both originating in plumes and flows from the tidally driven volcanoes. A broad, 1-micron band is found at high latitudes and may be due to absorption by long-chain sulfur polymers produced by SO2 radiolysis, although iron and iron sulfide compounds are candidates. An unidentified 3.15 micron absorber is equatorially distributed while a 4.62 micron band, perhaps due to a sulfate compound, exhibits a non-uniform distribution. Hot spots are generally dark, and some exhibit negative reflectance slopes (i.e., blue). The composition of these lavas has not been established spectroscopically, but the high temperatures of some volcanoes suggest ultramafic silicates or perhaps more refractory material such as oxides.

Carlson, R. W.↗
NASA NTRS1991

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

A relatively weak IR absorption feature detected at 1200 resolving power in Io at 2.1253 microns does not correspond to any gas- or solid-phase absorption expected on the basis of previously identified Io surface constituents. The source material of the feature appears to be stable and more uniformly distributed in longitude than Io's hot spots. These characteristics imply the feature's participation in a class different from those of other Io absorption spectrum features, thereby potentially serving as a major indicator of Io's atmosphere-surface composition and interactions. Results of laboratory experiments with plausible surface ices are compared with these observations.

Trafton, L. M.↗
NASA NTRS1992

Galileo Ultraviolet Spectrometer experiment

The Galileo ultraviolet spectrometer experiment uses data obtained by the Ultraviolet Spectrometer (UVS) mounted on the pointed orbiter scan platform and from the Extreme Ultraviolet Spectrometer (EUVS) mounted on the spinning part of the orbiter with the field of view perpendicular to the spin axis. The UVS is a Ebert-Fastie design that covers the range 113-432 nm with a wavelength resolution of 0.7 nm below 190 and 1.3 nm at longer wavelengths. The UVS spatial resolution is 0.4 deg x 0.1 deg for illuminated disk observations and 1 deg x 0.1 deg for limb geometries. The EUVS is a Voyager design objective grating spectrometer, modified to cover the wavelength range from 54 to 128 nm with wavelength resolution 3.5 nm for extended sources and 1.5 nm for point sources and spatial resolution of 0.87 deg x 0.17 deg. The EUVS instrument will follow up on the many Voyager UVS discoveries, particularly the sulfur and oxygen ion emissions in the Io torus and molecular and atomic hydrogen auroral and airglow emissions from Jupiter. The UVS will obtain spectra of emission, absorption, and scattering features in the unexplored, by spacecraft, 170-432 nm wavelength region. The UVS and EUVS instruments will provide a powerful instrument complement to investigate volatile escape and surface composition of the Galilean satellites, the Io plasma torus, micro- and macro-properties of the Jupiter clouds, and the composition structure and evolution of the Jupiter upper atmosphere.

Hord, C. W.↗
NASA NTRS1977

Voyager mission description

The Voyager project, which involves the 1977 launch of two advanced three-axis attitude stabilized spacecraft for the exploration of the Jovian and Saturnian systems, as well as interplanetary space, is discussed. The missions include investigation of the gravitational fields, atmospheric dynamics and magnetospheres of Jupiter and Saturn, the atmospheres, surface composition and features of Titan, the Io flux tube, the Great Red Spot of Jupiter, and earth occultation by Saturn's rings. To reduce energy required to reach Saturn, gravity-assist swingbys of Jupiter will be employed; a continuation to Uranus by the second satellite may be implemented by reliance on gravity-assist at Saturn.

Kohlhase, C. E.↗
NASA NTRS1982

Composition of the surfaces of the Galilean satellites

Sulfur chemistry on Io and the surface chemistry of the icy Galilean satellites are discussed in terms of laboratory chemical findings and spectral investigations. Gaseous, liquid, and solid allotropes of sulfur are described and related to spectral data for Io. Compounds of sulfur identified on Io's surface are given and possible mechanisms for their formation are evalutated. Laboratory studies of water frost, ice, and mixtures with other minerals are discussed and their relevance in interpreting infrared spectra of the icy Galilean satellites and the apparent solid water absorption band profiles is shown.

Sill, G. T.↗
NASA NTRS1980

The surface composition of Amalthea

It is proposed that charged particles from the Jovian magnetosphere, contaminants such as sulfur from Io, and high-velocity micrometeoritic matter, combine to darken, redden, and alter the surface of Amalthea revealed by Voyager; whose few isolated bright spots have a distinct greenish spectrum. A major finding of this analysis is that available spectral reflectance data contain little information about the bulk composition of the satellite. The effects of contamination by sulfur and its allotropes are shown to redden a variety of bulk compositions: carbonaceous material, refractory minerals, iron and iron sulfides, and moderate temperature silicates. The bright, greenish spots probably identify locations in which atypical alteration processes occur, such as variations in the amount of contaminant sulfur in micrometeoritic glasses or in the relative abundances of certain sulfur allotropes.

Gradie, J.↗
NASA NTRS1979

Preliminary geological mapping of Io

A preliminary summary of information gained by Voyager 1 on the colored, terrain and landform surface units of Io and their global distribution is presented. Colored units are classified as white to bluish-white regions which may be sulfur or sulfur dioxide deposits, red, orange, or yellow regions thought to contain various sublimates or alterations of sulfur, brownish regions limited to the polar areas and dark brown areas surrounding some vents. Terrain features observed include plains broken by scarps, isolated mountainous regions and volcanic vents resembling terrestrial caldera or pit craters. Maps of the distribution of these features, compiled by photogeological mapping techniques developed for terrestrial volcanic mapping, are presented, and the implications of the surface unit distributions for the volcanology, crustal composition, internal convection patterns and surface age of Io are discussed.

Masursky, H.↗
NASA NTRS2004

X-ray Probes of Magnetospheric Interactions with Jupiter's Auroral zones, the Galilean Satellites, and the Io Plasma Torus

Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the Jovian system is a source of x-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are powerful sources of x-ray emission. Chandra observations revealed x-ray emission from the Io Plasma Torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from these moons is certainly due to bombardment of their surfaces of highly energetic protons, oxygen and sulfur ions from the region near the Torus exciting atoms in their surfaces and leading to fluorescent x-ray emission lines. Although the x-ray emission from the Galilean moons is faint when observed fiom Earth orbit, an imaging x-ray spectrometer in orbit around these moons, operating at 200 eV and above with 150 eV energy resolution, would provide a detailed mapping (down to 40 m spatial resolution) of the elemental composition in their surfaces. Here we describe the physical processes leading to x-ray emission fiom the surfaces of Jupiter's moons and the instrumental properties, as well as energetic ion flux models or measurements, required to map the elemental composition of their surfaces. We discuss the proposed scenarios leading to possible surface compositions. For Europa, the two most extreme are (1) a patina produced by exogenic processes such as meteoroid bombardment and ion implantation, and (2) upwelling of material fiom the subsurface ocean. We also describe the characteristics of X - m , an imaging x-ray spectrometer under going a feasibility study for the JIM0 mission, with the ultimate goal of providing unprecedented x-ray studies of the elemental composition of the surfaces of Jupiter's icy moons and Io, as well as of Jupiter's auroral x-ray emission.

Elsner, R. F.↗
NASA NTRS2004

X-MIME: An Imaging X-ray Spectrometer for Detailed Study of Jupiter's Icy Moons and the Planet's X-ray Aurora

Remote observations with the Chandra X-ray Observatory and the XMM-Newton Observatory have shown that the Jovian system is a source of x-rays with a rich and complicated structure. The planet's polar auroral zones and its disk are powerful sources of x-ray emission. Chandra observations revealed x-ray emission from the Io Plasma Torus and from the Galilean moons Io, Europa, and possibly Ganymede. The emission from these moons is certainly due to bombardment of their surfaces of highly energetic protons, oxygen and sulfur ions from the region near the Torus exciting atoms in their surfaces and leading to fluorescent x-ray emission lines. Although the x-ray emission from the Galilean moons is faint when observed from Earth orbit, an imaging x-ray spectrometer in orbit around these moons, operating at 200 eV and above with 150 eV energy resolution, would provide a detailed mapping (down to 40 m spatial resolution) of the elemental composition in their surfaces. Such maps would provide important constraints on formation and evolution scenarios for the surfaces of these moons. Here we describe the characteristics of X-MIME, an imaging x-ray spectrometer under going a feasibility study for the JIMO mission, with the ultimate goal of providing unprecedented x-ray studies of the elemental composition of the surfaces of Jupiter's icy moons and Io, as well as of Jupiter's auroral x-ray emission.

Elsner, R. F.↗