Experiments demonstrate that partial evaporation of solid silica at 1600-1700 degrees C and low pressure (10(-9) bar) results in enrichment of O-18/O-16,d O-17/O-16 in solid products. Evaporative residues formed in H-2 or N-2 gas at higher pressures (>10(-5) bar) exhibit limited or negligible heavy isotope enrichment. The degree of enrichment is controlled by kinetic fractionation at the ablating grain surfaces, the rate of sublimation, and the efficacy of oxygen self diffusion in the solid. Observed isotopic effects are consistent with numerical simulations, confirming that vaporization of solid silicate and oxide minerals is a viable cause for non-Rayleigh fractionation of O-16, O-17, and O-18. Experiment and theory suggest that partial melting during evaporation is not required a priori to explain mass-dependent variations in oxygen isotope ratios in primitive meteoritical materials. Experimental determinations of the rates of ablation of appropriate minerals are required to evaluate the meteoritical data.

Experiments were performed to test the viability of using isotope-ratio-monitoring gas-chromatography mass spectrometry (irm-GCMS) as a means for isotopic analysis of nanomole quantities of O-2 released in a vacuum system suitable for laser extraction and fluorination. Several sources of error were identified and eliminated, including false signals from extraneous scattered ions and adsorption of O-2 to metal surfaces. Results show that with appropriate attention to these potential impediments, coupling high-precision irm-GCMS to laser sampling of microgram quantities of silicate and oxide minerals is feasible. Copyright (C) 1998 Elsevier Science Ltd.

Alteration of the Allende meteorite caused shifts in oxygen isotope ratios along a single mass fractionation Line, if alteration was caused by aqueous fluid, the pattern of oxygen isotope fractionation can be explained only by flow of reactive water down a temperature gradient. Down-temperature flow of aqueous fluid within planetesimals is sufficient to explain the mineralogical and oxygen isotopic diversity among CV, CM, and CI carbonaceous chondrites and displacement of the terrestrial planets from the primordial slope 1.00 line on the oxygen three-isotope plot.

We analyze Spitzer and Magellan observations of a star-forming core near IRS 2 in the young cluster NGC 2264. The submillimeter source IRAS 12 S1, previously believed to be an intermediate-mass Class 0 object is shown to be a dense collection of embedded, low-mass stars. We argue that this group of stars represents the fragmenting collapse of a dense, turbulent core, using a number of indicators of extreme youth. With reasonable estimates for the velocity dispersion in the group, we estimate a dynamical lifetime of only a few times 10(4) yr. Spectral energy distributions of stars in the core are consistent with Class I or Class 0 assignments. We present observations of an extensive system of molecular hydrogen emission knots. The luminosity of the objects in the core region are consistent with roughly solar mass protostars.

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single O-17-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is O-16-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (MontgolfiSre) and possibly several landing probes to be delivered through the atmosphere.