The stability of Ti-bearing crystalline phases such as rutile and ilmenite in the Earth's interior can be dependent on the solubility behavior of TiO2 in aqueous fluids. Natural and experimental evidence indicate that significant TiO2 mobility is possible in this environment.

Bisulfite (HSO3-) and sulfite (SO32-) compounds play key roles in numerous geochemical and biochemical processes extending from the atmosphere to the subseafloor biosphere. Despite decades of spectroscopic investigations, the molecular composition of HSO3-in solution remains uncertain and, thus, the role of bisulfite in (bio) chemical and isotope fractionation processes is unclear. We report new experimental estimates for the bisulfite isomer quotient (Q(i) = [(HO)SO2-]/[(HS)O-3(-)]; [] = concentration) as a function of temperature from the interpretation of Raman spectra collected from aqueous NaHSO3 solutions contained in fused silica capsules. In pure NaHSO3 solutions (1Na(+): 1HSO(3)(-), stoichiometric) over [NaHSO3] = 0.2-0.4 m (moles/kg H2O), the following relationship is obtained:

The terrestrial nitrogen budget, distribution, and evolution are governed by biological and geological recycling. The biological cycle provides the nitrogen input for the geological cycle, which, in turn, feeds some of the nitrogen into the Earth's interior. A portion of the nitrogen also is released back to the oceans and the atmosphere via N-2 degassing. Nitrogen in silicate minerals (clay minerals, mica, feldspar, garnet, wadsleyite, and bridgmanite) exists predominantly as NH4+. Nitrogen also is found in graphite and diamond where it occurs in elemental form. Nitrides are stable under extremely reducing conditions such as those that existed during early planetary formation processes and may still persist in the lower mantle. From experimentally determined nitrogen solubility in such materials, the silicate Earth is nitrogen undersaturated. The situation for the core is more uncertain, but reasonable Fe metal/silicate nitrogen partition coefficients (>10) would yield nitrogen contents sufficient to account for the apparent nitrogen deficiency in the silicate Earth compared with other volatiles. Transport of nitrogen takes place in silicate melt (magma), water-rich fluids, and as a minor component in silicate minerals. In melts, the N solubility is greater for reduced nitrogen, whereas the opposite appears to be the case for N solubility in fluids. Reduced nitrogen species (NH3, NH2-, and NH2+) dominate in most environments of the modern Earth's interior except the upper similar to 100 km of subduction zones where N-2 is the most important species. Nitrogen in magmatic liquids in the early Earth probably was dominated by NH3 and NH2-, whereas in the modern Earth, the less reduced, NH2+ functional group is more common. N-2 is common in magmatic liquids in subduction zones. Given the much lower solubility of N-2 in magmatic liquids compared with other nitrogen species, nitrogen dissolved as N-2 in subduction zone magmas is expected to be recycled and returned to the oceans and the atmosphere, whereas nitrogen in reduced form(s) likely would be transported to greater depths. This solubility difference, controlled primarily by variations in redox conditions, may be a factor resulting in increased nitrogen in the Earth's mantle and decreasing abundance in its oceans and atmosphere during the Earth's evolution. Such an abundance evolution has resulted in the decoupling of nitrogen distribution in the solid Earth and the hydrosphere and atmosphere.

An understanding of the mechanisms of Ti is incorporation into silicate glasses and melts is critical for the field of petrology. Trace-element thermobarometry, high-field-strength element partitioning, and the physical properties of magmas are all be influenced by Ti incorporation into glasses and changes therein in response to changes in composition and temperature. In this study, we combine Si-29 solid state NMR and Ti K-edge XAFS spectroscopy to investigate how Ti is incorporated into quenched Na-silicate glasses, and the influence of Ti on the structure of silicate species in these glasses. Si-29 NMR shows that in both Ti-bearing Na2O center dot 4SiO(2) (NS4) and Na2O center dot 8SiO(2) (NS8) glasses, increasing the amount of Ti in the melt results in a shift of Si Q(4) peak in the Si-29 NMR spectra reflecting Ti nearest neighbors for Si in Q(4) speciation. The Ti XAFS results from NS8 glass indicate that Ti is primarily incorporated in [5]-fold coordination. At higher Ti content, there is a shift of the XAFS pre-edge feature suggesting mixing of [4]-fold Ti into the spectra. Combined, the Si-29 NMR and XAFS pre-edge data are consistent with Ti incorporation as isolated Ti-[5] atoms and the formation of Ti-[5] clusters at relatively low Ti concentrations, with no evidence for Ti-Na interactions as suggested by previous studies. As the Ti content increases, the Ti atoms begin to occupy 4-fold coordinated sites interacting primarily with Si in Q(4) speciation (no significant Na-([4]) Ti bonding). The internal consistency of these two techniques provides a uniquely complete snapshot of the complexity of Ti incorporation in silicate melts and underlies the importance of understanding Ti incorporation mechanisms in natural magmatic systems.

An estimate of TiO2 activity (alpha(melt-sat)(TiO2)) is necessary for the application of trace-element thermobarometry of magmatic systems where melts are typically undersaturated with respect to rutile/anatase. Experiments were performed in the system SiO2-Na2O-TiO2 to develop two independent methods of estimating alpha(melt-sat)(TiO2)-one based on the commonly applied rutile-saturation technique and another utilizing a novel Ti-in-tridymite thermometer. It is demonstrated that the rutile-saturation model can lead to an overestimate of alpha(melt-sat)(TiO2) relative to TiO2 activity calculated using the solubility of Ti in tridymite (SiO2) coexisting with rutile. Overestimation via the rutile-saturation technique is due to variations in the solubility mechanisms of Ti in the melt phase as a function of Ti content. In natural systems, overestimates of alpha(melt-sat)(TiO2) will lead to an underestimation of crystallization temperatures by Ti-based trace-element thermobarometers. Although this study is not directly applicable to natural systems, it lays the groundwork for future research on natural composition magmas to constrain TiO2 activity in melts.

Aluminosilicate glasses and melts are of paramount importance for geo-and materials sciences. They include most mag-mas, and are used to produce a wide variety of everyday materials, from windows to smartphone displays. Despite this impor-tance, no general model exists with which to predict the atomic structure, thermodynamic and viscous properties of aluminosilicate melts. To address this, we introduce a deep learning framework, 'i-Melt', which combines a deep artificial neu-ral network with thermodynamic equations. It is trained to predict 18 different latent and observed properties of melts and glasses in the K2O-Na2O-Al2O3-SiO2 system, including configurational entropy, viscosity, optical refractive index, density, and Raman signals. Viscosity can be predicted in the 10(0)-10(15) log(10) Pa.s range using five different theoretical frameworks (Adam-Gibbs, Free Volume, MYEGA, VFT, Avramov-Milchev), with a precision equal to, or better than, 0.4 log(10) Pa.s on unseen data. Density and optical refractive index (through the Sellmeier equation) can be predicted with errors equal or lower than 0.02 and 0.006, respectively. Raman spectra for K2O-Na2O-Al2O3-SiO2 glasses are also predicted, with a rel-atively high mean error of similar to 25% due to the limited data set available for training. Latent variables can also be predicted with good precisions. For example, the glass transition temperature, T-g, can be predicted to within 19 K, while the melt configu-rational entropy at the glass transition, S-conf(T-g), can be predicted to within 0.8 J mol(-1) K-1.

In peralkaline and meta-aluminous melts, essentially all Al3+ (> 95%) occupy tetrahedral coordination, whereas for peraluminous melts, complex mixtures of aluminum triclusters with 4-fold coordinated Al3+ and Al3+ in 5- and 6-fold coordination with oxygen describe the structure. Aluminum in tetrahedral coordination requires electrical charge-balance. With alkali metals (M+) in this role, the proportions are M+=Al3+. The overall structure is dominated by three-dimensionally interconnected tetrahedra to form 6-membered rings of tetrahedra. The Al/(Al+Si) of these tetrahedra are simple positive functions of the bulk melt Al/(Al+Si). When tetrahedrally-coordinated Al3+ is charge-balanced by divalent cations, the M2+ cation charge-balances 2Al(3+) tetrahedrally coordinated cations. This structure is dominated by SiO4, (Si,Al)O-4, and AlO4 entities.

We have surveyed the Hill sphere of Mars for irregular satellites. Our search covered nearly the entire Hill sphere, but scattered light from Mars excluded the inner few arcminutes where the satellites Phobos and Deimos reside. No new satellites were found to an apparent limiting red magnitude of 23.5, which corresponds to radii of about 0.09 km using an albedo of 0.07.

We present a deep optical survey of Uranus's Hill sphere for small satellites. The 8 m Subaru Telescope was used to survey about 3.5 square degrees with a 50% detection efficiency at limiting red magnitude m(R) = 26.1. This magnitude corresponds to objects that are about 7 km in radius (assuming an albedo of 0.04). We detected ( without prior knowledge of their positions) all previously known outer satellites and discovered two new irregular satellites (S/2001 U2 and S/2003 U3). The two inner satellites Titania and Oberon were also detected. One of the newly discovered bodies (S/2003 U3) is the first known irregular prograde satellite of the planet. The population, size distribution, and orbital parameters of Uranus's irregular satellites are remarkably similar to those of the irregular satellites of gas giant Jupiter. Both have shallow size distributions (power-law indices q similar to 2 for radii larger than 7 km) with no correlation between the sizes of the satellites and their orbital parameters. However, unlike those of Jupiter, Uranus's irregular satellites do not appear to occupy tight, distinct dynamical groups in semimajor-axis versus inclination phase space. Two groupings in semimajor-axis versus eccentricity phase space appear to be statistically significant.

A detailed description of the Halley-type Comet C/2001 OG(108) (LONEOS) has been derived from visible, near-infrared, and mid-infrared observations obtained in October and November 2001. These data represent the first high-quality ground-based observations of a bare Halley-type comet nucleus and provide the best characterization of a Halley-type comet other than 1P/Halley itself. Analysis of time series photometry suggests that the nucleus has a rotation period of 57.2 +/- 0.5 h with a minimum nuclear axial ratio of 1.3, a phase-darkening slope parameter G of -0.01 +/- 0.10, and an estimated H = 13.05 +/- 0.10. The rotation period of C/2001 OG(108) is one of the longest observed among comet nuclei. The V-R color index for this object is measured to be 0.461 +/- 0.02, which is virtually identical to that of other cometary nuclei and other possible extinct comet candidates. Measurements of the comet's thermal emission constrain the projected elliptical nuclear radii to be 9.6 +/- 1.0 km and 7.4 +/- 1.0 km, which makes C/2001 OG(108) one of the larger cometary nuclei known. The derived geometric albedo in V-band of 0.040 +/- 0.010 is typical for comet nuclei. Visible-wavelength spectrophotometry and near-infrared spectroscopy were combined to derive the nucleus's reflectance spectrum over a 0.4 to 2.5 mu m wavelength range. These measurements represent one of the few nuclear spectra ever observed and the only known spectrum of a Halley-type comet. The spectrum of this comet nucleus is very nearly linear and shows no discernable absorption features at a 5% detection limit. The lack of any features, especially in the 0.8 to 1.0 mu m range such as are seen in the spectra of carbonaceous chondrite meteorites and many low-albedo asteroids, is consistent with the presence of anhydrous rather than hydrous silicates on the surface of this comet. None of the currently recognized meteorites in the terrestrial collections have reflectance spectra that match C/2001 OG(108). The near-infrared spectrum, the geometric albedo, and the visible spectrophotometry all indicate that C/2001 OG(108) has spectral properties analogous to the D-type, and possibly P-type asteroids. Comparison of the measured albedo and diameter of C/2001 OG(108) with those of Damocloid asteroids reveals similarities between these asteroids and this comet nucleus, a finding which supports previous dynamical arguments that Damocloid asteroids could be composed of cometary-like materials. These observations are also consistent with findings that two Jupiter-family comets may have spectral signatures indicative of D-type asteroids. C/2001 OG(108) probably represents the transition from a typical active comet to an extinct cometary nucleus, and, as a Halley-type comet, suggests that some comets originating in the Oort cloud can become extinct without disintegrating. As a near-Earth object, C/2001 OG(108) supports the suggestion that some fraction of the near-Earth asteroid population consists of extinct cometary nuclei. (c) 2005 Elsevier Inc. All rights reserved.