Search

Sulfuric acid hydrate has been proposed as an important species on Europa's surface, the acid being produced by radiolysis of surficial sulfur compounds. We investigated the spectral properties of disordered and crystalline forms of sulfuric acid and suggest that the hydration properties of Europa's hypothesized sulfuric acid lie between two end members: liquid sulfuric acid and its higher crystalline hydrates. The spectra of these end members are similar except for spectral shifts at the band edges. We measured the optical constants of sulfuric acid octahydrate and used these with simple radiative transfer calculations to fit Europa spectra obtained by Galileo's Near Infrared Mapping Spectrometer (NIMS). The global distribution of the hydrate that we associate here with hydrated sulfuric acid shows a strong trailing-side enhancement with a maximum fractional hydrate abundance of 90% by volume, corresponding to a sulfur atom to water molecule ratio of 10%. The hydrate concentration spatially correlates with the ultraviolet and visible absorption of the surface and with the sulfur dioxide concentration. The asymmetric global distribution is consistent with Iogenic plasma ion implantation as the source of the sulfur, possibly modified by electron irradiation and sputtering effects. The variegated distribution also correlates with geologic forms. A high spatial resolution image shows resolved lineae with less hydrate appearing within the lineae than in nearby crustal material. The low concentration of hydrated material in these lineae argues against their conveying sulfurous material to the surface from the putative ocean.

Infrared spectral images of Jupiter's volcanic moon Io, acquired during the October and November 1999 and February 2000 flybys of the Galileo spacecraft, were used to study the thermal structure and sulfur dioxide distribution of active volcanoes. Loki Patera, the solar system's most powerful known volcano, exhibits large expanses of dark, cooling lava on its caldera floor. Prometheus, the site of long-lived plume activity, has two major areas of thermal emission, which support ideas of plume migration. Sulfur dioxide deposits were mapped at local scales and show a more complex relationship to surface colors than previously thought, indicating the presence of other sulfur compounds.

Io's volcanic activity has been monitored by instruments aboard the Galileo spacecraft since June 28, 1996. We present results from observations by the Near-Infrared Mapping Spectrometer (NIM) for the first ten orbits of Galileo, correlate them with results from the Solid State Imaging System (SSI)and from ground-based observations, and compare them to what was known about Io's volcanic activity from observations made during the two Voyager fly-bys in 1979.

The Galileo Near Infrared Mapping Spectrometer was used to investigate the distribution and properties of sulfur dioxide over the surface of Io, and qualitative results for the anti-Jove hemisphere are presented here. SO2, existing as a frost, is found almost everywhere, but with spatially variable concentration. The exceptions are volcanic hot spots, where high surface temperatures promote rapid vaporization and can produce SO2-free areas. The pervasive frost, if fully covering the cold surface, has characteristic grain sizes of 30 to 100 µm, or greater. Regions of greater sulfur dioxide concentrations are found. The equatorial Colchis Regio area exhibits extensive snowfields with large particles (250 to 500 µm diameter, or greater) beneath smaller particles. A weak feature at 3.15 µm is observed and is perhaps due to hydroxides, hydrates, or water. A broad absorption in the 1 µm region, which could be caused by iron-containing minerals, shows a concentration in Io's southern polar region, with an absence in the Pele plume deposition ring.

The Near-Infrared Mapping Spectrometer on Galileo has monitored the volcanic activity on Io since June 28, 1996. This paper presents preliminary analysis of NIMS thermal data for the first four orbits of the Galileo mission. NIMS has detected 18 new hot spots and 12 others which were previously known to be active. The distribution of the hot spots on Io's surface may not be random, as hot spots surround the two bright, SO2-rich regions of Bosphorus Regio and Colchis Regio. Most hot spots scan to be persistently active from orbit to orbit and 10 of those detected were active in 1979 during the Voyager encounters. We report the distribution of hot spot temperatures and find that they are consistent with silicate volcanism.

International audience; Recent improvements in a comprehensive non-local thermodynamic equilibrium (non-LTE) model of CO 2 atmospheres has permitted a better understanding of a number of Venusian atmospheric measurements taken more than a decade ago by the "Near Infrared Mapping Spectrometer" (NIMS) on board the Galileo spacecraft during its Venus fly-by. Those data, containing a strong non-LTE component, showed a structure in the 4.3-mum spectral region which was challenging for non-LTE models so far. The model used in this work was refined after analysis of Martian CO 2 atmospheric emission taken by the "Planetary Fourier Spectrometer" (PFS) and the "Visible and Infrared Mineralogical Mapping Spectrometer" (OMEGA) instruments on board Mars Express. Here we show that both the limb and the nadir measurements of the Venus daylight atmosphere taken at 4.3-mum by NIMS can be fitted reasonably well with the revised model. This gives confidence in the usage of such model for the analysis of the Venus Express mission, in particular for the "Visible Infrared Thermal Imaging Spectrometer" (VIRTIS) instrument which will systematically observe these emissions. We present here non-LTE simulations for VIRTIS which demonstrate its capabilities and potential for detecting atmospheric emissions of CO and CO 2 under non-LTE, both in limb and nadir observations and we discuss briefly the perspectives to use them in order to improve our understanding of the physics of the upper atmosphere of Venus.

This article discusses a study conducted on patients who underwent prophylactic endodontic treatment. It compares the incidence of flare-ups in allergic and nonallergic patients. The authors further relate this study to one conducted in a previous article.

This paper presents the analysis of hot spot observations in the Jovian North Equatorial Belt obtained with the near-infrared mapping spectrometer (NIMS) instrument on the Galileo spacecraft. The data were acquired during the closest approach sequences between June 1996 and April 1997. We focus on the spectral window between 4.5 and 5.2 [Jim determining the cloud opacity above 2 bar, the water vapor relative humidity, and the ammonia abundance between 4 and 8 bar. We find a linear relationship between the cloud opacity and the continuum level of the spectrum. For a given radiance level of an individual spectrum, significant variations in the water vapor relative humidity are seen. However, no clear evidence for a relationship between the cloud opacity and the water relative humidity is seen. A cloud structure similar to that measured by the Galileo entry probe, with no significant cloud opacity below 2 bar, is adequate. The air in the hot spots is found to be overall dry, consistent with the probe measurements. None of the considered spectra show water vapor relative humidities exceeding 10%. Significant spatial variations of the water vapor relative humidity are found, and the distribution over the observed hot spot regions is complex. Because of a low sensitivity of the NIMS spectra to ammonia, uncertainties in the derived ammonia abundance are much higher than for water. There is, however, a possible trend in all the observed hot spots toward more ammonia inside than outside the hot spots at the sounded pressure levels. Copyright 1998 by the American Geophysical Union.

Galileo's Near-Infrared Mapping Spectrometer (NIMS) observed Io during the spacecraft's three flybys in October 1999, November 1999, and February 2000. The observations, which are summarized here, were used to map the detailed thermal structure of active volcanic regions and the surface distribution of SO2 and to investigate the origin of a yet unidentified compound showing an absorption feature at ---1 m. We present a summary of the observations and results, focusing on the distribution of thermal emission and of SO2 deposits. We find high eruption temperatures, consistent with ultramafic volcanism, at Pele. Such temperatures may be present at other hot spots, but the hottest areas may be too small for those temperatures to be detected at the spatial resolution of our observations. Loki is the site of frequent eruptions, and the low thermal emission may represent lavas cooling on the caldera's surface or the cooling crust of a lava lake. High- resolution spectral observations of Emakong caldera show thermal emission and SO2 within the same pixels, implying that patches of SO2 frost and patches of cooling lavas or sulfur flows are present within a few kilometers from one another. Thermal maps of Prometheus and Amirani show that these two hot spots are characterized by long lava flows. The thermal profiles of flows at both locations are consistent with insulated flows, with the Amirani flow field having more breakouts of fresh lava along its length. Prometheus and Amirani each show a white ring at visible wavelengths, while SO2 distribution maps show that the highest concentration of SO2 in both ring deposits lies outside the white portion. Visible measurements at high phase angles show that the white deposit around Prometheus extends into the SO2 ring. This suggests that the deposits are thin and that compositional or grain size variations may occur in the radial direction. SO2 mapping of the Chaac region shows that the interior of a caldera adjacent to Chaac has almost pure SO2. The deposit appears to be topographically controlled, suggesting a possible origin by liquid flow.