Search

A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance-compositional-structural relations for this group of minerals. Sulfates exhibit diverse spectral properties, and absorption-band assignments have been developed for the 0.3-26 [micro]m range. Sulfate absorption features can be related to the presence of transition elements, OH, [H.sub.2]O, and S[O.sub.4] groups. The number, wavelength position, and intensity of these bands are a function of both composition and structure. Cation substitutions can affect the wavelength positions of all major absorption bands. Hydroxo-bridged [Fe.sup.3+] results in absorption bands in the 0.43, 0.5, and 0.9 [micro]m regions, while the presence of [Fe.sup.2+] results in absorption features in the 0.9-1.2 [micro]m interval. Fundamental S-O bending and stretching vibration absorption bands occur in the 8-10, 13-18, and 19-24 [micro]m regions (1000-1250, 550-770, and 420-530 [cm.sup.- 1]). The most intense combinations and overtones of these fundamentals are found in the 4-5 [micro]m (2000-2500 [cm.sup.-1]) region. Absorption features seen in the 1.7-1.85 [micro]m interval are attributable to H-OH/O-H bending and translation/rotation combinations, while bands in the 2.1-2.7 [micro]m regions can be attributed to [H.sub.2]O- and OH-combinations as well as overtones of S-O bending fundamentals. OH- and [H.sub.2]O-bearing sulfate spectra are fundamentally different from each other at wavelengths below ~6 [micro]m. Changes in [H.sub.2]O/OH content can shift S-O band positions due to change in bond lengths and structural rearrangement. Differences in absorption band wavelength positions enable discrimination of all the sulfate minerals used in this study in a number of wavelength intervals. Of the major absorption band regions, the 4-5 [micro]m region seems best for identifying and discriminating sulfates in the presence of other major rock-forming minerals. Keywords: Asteroids, composition; Europa; Mars, surface; Meteorites; Mineralogy; Spectroscopy

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.01.015 Byline: Ashley Gerard Davies, Dennis L. Matson, Glenn J. Veeder, Torrence V. Johnson, Diana L. Blaney Abstract: The modeling of thermal emission from active lava flows must account for the cooling of the lava after solidification. Models of lava cooling applied to data collected by the Galileo spacecraft have, until now, not taken this into consideration. This is a flaw as lava flows on Io are thought to be relatively thin with a range in thickness from [approximately equal to]1 to 13 m. Once a flow is completely solidified (a rapid process on a geological time scale), the surface cools faster than the surface of a partially molten flow. Cooling via the base of the lava flow is also important and accelerates the solidification of the flow compared to the rate for the 'semi-infinite' approximation (which is only valid for very deep lava bodies). We introduce a new model which incorporates the solidification and basal cooling features. This model gives a superior reproduction of the cooling of the 1997 Pillan lava flows on Io observed by the Galileo spacecraft. We also use the new model to determine what observations are necessary to constrain lava emplacement style at Loki Patera. Flows exhibit different cooling profiles from that expected from a lava lake. We model cooling with a finite-element code and make quantitative predictions for the behavior of lava flows and other lava bodies that can be tested against observations both on Io and Earth. For example, a 10-m-thick ultramafic flow, like those emplaced at Pillan Patera in 1997, solidifies in [approximately equal to]450 days (at which point the surface temperature has cooled to [approximately equal to]280 K) and takes another 390 days to cool to 249 K. Observations over a sufficient period of time reveal divergent cooling trends for different lava bodies [examples: lava flows and lava lakes have different cooling trends after the flow has solidified (flows cool faster)]. Thin flows solidify and cool faster than flows of greater thickness. The model can therefore be used as a diagnostic tool for constraining possible emplacement mechanisms and compositions of bodies of lava in remote-sensing data. Author Affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA

The modeling of thermal emission from active lava flows must account for the cooling of the lava after solidification. Models of lava cooling applied to data collected by the Galileo spacecraft have, until now, not taken this into consideration. This is a flaw as lava flows on Io are thought to be relatively thin with a range in thickness from ~1 to 13 m. Once a flow is completely solidified (a rapid process on a geological time scale), the surface cools faster than the surface of a partially molten flow. Cooling via the base of the lava flow is also important and accelerates the solidification of the flow compared to the rate for the 'semi-infinite' approximation (which is only valid for very deep lava bodies). We introduce a new model which incorporates the solidification and basal cooling features. This model gives a superior reproduction of the cooling of the 1997 Pillan lava flows on Io observed by the Galileo spacecraft. We also use the new model to determine what observations are necessary to constrain lava emplacement style at Loki Patera. Flows exhibit different cooling profiles from that expected from a lava lake. We model cooling with a finite-element code and make quantitative predictions for the behavior of lava flows and other lava bodies that can be tested against observations both on Io and Earth. For example, a 10-m-thick ultramafic flow, like those emplaced at Pillan Patera in 1997, solidifies in ~450 days (at which point the surface temperature has cooled to ~280 K) and takes another 390 days to cool to 249 K. Observations over a sufficient period of time reveal divergent cooling trends for different lava bodies [examples: lava flows and lava lakes have different cooling trends after the flow has solidified (flows cool faster)]. Thin flows solidify and cool faster than flows of greater thickness. The model can therefore be used as a diagnostic tool for constraining possible emplacement mechanisms and compositions of bodies of lava in remote-sensing data. Keywords: Jupiter; Io; Volcanism; Lava flow; Lava lake; Thermal; Modeling

Near-infrared spectroscopic imaging of a bright region within the Mars seasonal south polar cap was conducted during southern spring ([L.sub.s] = 231) near the 2003 opposition, using the NASA Infrared Telescope Facility. The measured spectra are well represented by C[O.sub.2] ice with grain radius of 13 mm and admixed dust and water ice concentrations of 0.005 and 0.002 wt%, respectively. We present a representative spectral (0.2-100 [micro]m) surface albedo for the bright region. Keywords: Mars; Ices; Infrared observations; Spectroscopy

Polar brightness temperatures on Io are higher than expected for any passive surface heated by absorbed sunlight. This discrepancy implies large scale volcanic activity from which we derive a new component of Io's heat flow. We present a 'Three Component' thermal background, infrared emission model for Io that includes active polar regions. The widespread polar activity contributes an additional ~0.6 W [m.sup.-2] to Io's heat flow budget above the ~2.5 W [m.sup.-2] from thermal anomalies, Our estimate for Io's global average heat flow increases to ~3 [+ or -] 1 W [m.sup.-2] and ~1.3 [+ or -] 0.4 x [10.sup.14] watts total. Keywords: Io; Volcanism; Thermal; Infrared

We report high-spectral-resolution ([lambda]/[delta][lambda])t = 800-2300) near-infrared mapping observations of Mars at [L.sub.s] = 130[degrees] (April 1999), which were obtained by drift-scanning the cryogenic long-slit spectrometer at the KPNO 2.2-m telescope across the disk. Data were reformatted into calibrated spectral image cubes (x,y,[lambda]) spanning 2.19 to 4.12 [micro]m, which distinguish atmospheric C[O.sub.2] features, solar lines, and surface and aerosol features. Maps of relative band depth between 3.0 and 3.5 [micro]m trace water ice clouds and show the diurnal evolution of features in the persistent northern summer aphelion cloud belt, which was mapped contemporaneously but at fixed local time by the Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES). Cloud optical depth, particle sizes, and ice aerosol content were estimated using a two-stream, single-layer scattering model, with Mie coefficients derived from recently published ice optical constants, followed by a linear spectral deconvolution process. A comparison of data and model spectra shows evaporating nighttime clouds in the morning followed by afternoon growth of a prominent orographic cloud feature on the west flank of Elysium Mons. Cloud optical depth at 3.2/am evolved to 0.28 [+ or -] 0.13 and ice aerosol column abundance to 0.9 [+ or -] 0.3 pr [micro] in the afternoon. Column abundances as large as 0.17 pr [micro]m were retrieved in nonorographic clouds within the aphelion cloud band around midday. These clouds exhibit a modest decline in optical depth during the afternoon. Results show that ice particle radii from 4 [micro]m exist in both cloud types. However, large particles dominate the spectra, consistent with recent MGS/TES emission phase function measurements of aphelion cloud aerosol properties. Keywords: Mars; Mars atmosphere; infrared observations

A 10 [[micro]meter] silicate emission feature has been discovered in the spectra of comets P/Borrelly and P/Faye at R [approximately] 1.5 AU. These are the first short period comets in which silicate emission has definitely been detected. The broad emission features are about 25% above the continuum. No emission feature was present in the spectrum of P/Schaumasse; it is possible that the nucleus of P/Schaumasse was directly detected. If all of the observed flux originated from the nucleus, then the effective radius is about 3 km; the observed color temperature is consistent with a rapidly rotating nucleus. We present models that show how the shape of the silicate feature can depend on the way in which silicate and absorbing material are mixed in the grains.

Modeling of an infrared outburst on the Jovian satellite reveals that the outburst is caused by the flow of lava from a large volcanic eruption. The lava has an initial temperature of 1,225 Kelvin, which later cools down to 555 Kelvin. Many volcanic eruptions such as this have contributed to the absence of intact craters on the Jovian satellite.