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Before TES (Thermal Emission Spectrometry) spectra can be used to model surface compositions, they must have a strong atmospheric compensation applied. We explore a very different atmospheric retrieval process, and compare results and implications for the derived surface composition. Additional information is contained in the original extended abstract.
In this paper, we will provide insights into mass spectrometer requirements. In addition, we will describe the modeling of the neutrals ejected from likely surface materials and their ionization rates in the Jovian environment. We will use such models to connect the mass spectra measurements of the freshly formed ions to surface composition. We will also discuss what possible compositional signatures are for endogenic materials other than water ice. Finally, since a goal is to identify material composition with surface features, we will describe the transport of neutrals ejected from the surface prior to detection by either an ion or neutral mass spectrometer.
Recent findings of the MESSENGER mission on Mercury have brought new evidence for its reducing nature, widespread volcanism and surface compositional heteregeneity. MESSENGER also provided major elemental ratios of its surface that can be used to infer large-scale differentiation processes and the thermal history of the planet. Mercury is known as being very reduced, with very low Fe-content and high S and alkali contents on its surface. Its bulk composition is therefore likely close to EH enstatite chondrites. In order to elucidate the origin of the chemical diversity of Mercury's surface, we determined the melting properties of EH enstatite chondrites, at pressures between 1 bar and 3 GPa and oxygen fugacity of IW-3 to IW-5, using piston-cylinder experiments, combined with a previous study on EH4 melting at 1 bar. We found that the presence of Ca-rich sulfide melts induces significant decrease of Ca-content in silicate melts at low pressure and low degree of melting (F). Also at pressures lower than 3 GPa, the SiO2-content decreases with F, while it increases at 3 GPa. This is likely due to the chemical composition of the bulk silicate which has a (Mg+Fe+Ca)/Si ratio very close to 1 and to the change from incongruent to congruent melting of enstatite. We then tested whether the various chemical compositions of Mercury's surface can result from mixing between two melting products of EH chondrites. We found that the majority of the geochemical provinces of Mercury's surface can be explained by mixing of two melts, with the exception of the High-Al plains that require an Al-rich source. Our findings indicate that Mercury's surface could have been produced by polybaric melting of a relatively primitive mantle.
Surface segregation in Ni-Pd alloys has been studied using the BFS method for alloys. Not only does the method predict an oscillatory segregation profile but it also indicates that the number of Pd-enriched surface planes can vary as a function of orientation. The segregation profiles were computed as a function of temperature, crystal face, and composition. Pd enrichment of the first layer is observed in (111) and (100) surfaces, and enrichment of the top two layers occurs for (110) surfaces. In all cases, the segregation profile shows oscillations that are actually related to weak ordering tendencies in the bulk. An atom-by-atom analysis was performed to identify the competing mechanisms leading to the observed surface behaviors. Large-scale atomistic simulations were also performed to investigate the temperature dependence of the segregation profiles as well as for analysis of the bulk structures. Finally, the observed surface behaviors are discussed in relation to the bulk phase structure of Ni-Pd alloys, which exhibit a tendency to weakly order.
Despite being trace constituents of the lunar exosphere, sodium and potassium are the most readily observed species due to their bright line emission. Measurements of these species by the Ultraviolet and Visible Spectrometer (UVS) on the Lunar Atmosphere and Dust Environment Explorer (LADEE) have revealed unambiguous temporal and spatial variations indicative of a strong role for meteoroid bombardment and surface composition in determining the composition and local time dependence of the Moon's exosphere. Observations show distinct lunar day (monthly) cycles for both species as well as an annual cycle for sodium. The first continuous measurements for potassium show a more repeatable variation across lunations and an enhancement over KREEP (Potassium Rare Earth Elements and Phosphorus) surface regions, revealing a strong dependence on surface composition.
Dragonfly is a rotorcraft lander mission, selected as a finalist in NASA's New Frontiers Program, that is designed to sample materials and determine the surface composition in different geologic settings on Titan. This revolutionary mission concept would explore diverse locations to characterize the habitability of Titan's environment, to investigate how far prebiotic chemistry has progressed, and to search for chemical signatures that could be indicative of water-based and/or hydrocarbon-based life. Here we describe Dragonfly's capabilities to determine the composition of a variety of surface units on Titan, from elemental components to complex organic molecules. The compositional investigation ncludes characterization of local surface environments and finely sampled materials. The Dragonfly flexible sampling approach can robustly accommodate materials from Titan's most intriguing surface environments.
The surface of Pluto as it is understood on the eve of the encounter of the New Horizons spacecraft (mid-2015) consists of a spatially heterogeneous mix of solid N2, CH4, CO, C2H6, and an additional component that imparts color, and may not be an ice. The known molecular ices are detected by near-infrared spectroscopy. The N2 ice occurs in the hexagonal crystalline b-phase, stable at T greater than 35.6 K. Spectroscopic evidence for wavelength shifts in the CH4 bands attests to the complex mixing of CH4 and N2 in the solid state, in accordance with the phase diagram for N2 + CH4. Spectra obtained at several aspects of Plutos surface as the planet rotates over its 6.4-day period show variability in the distribution of CH4 and N2 ices, with stronger CH4 absorption bands associated with regions of higher albedo, in correlation with the visible rotational light curve. CO and N2 ice absorptions are also strongly modulated by the rotation period; the bands are strongest on the anti-Charon hemisphere of Pluto. Longer term changes in the strengths of Plutos absorption bands occur as the viewing geometry changes on seasonal time-scales, although a complete cycle has not been observed. The non-ice component of Plutos surface may be a relatively refractory material produced by the UV and cosmic-ray irradiation of the surface ices and gases in the atmosphere, although UV does not generally penetrate the atmospheric CH4 to interact with the surface. Laboratory simulations indicate that a rich chemistry ensues by the irradiation of mixtures of the ices known to occur on Pluto, but specific compounds have not yet been identified in spectra of the planet. Charons surface is characterized by spectral bands of crystalline H2O ice, and a band attributed to one or more hydrates of NH3. Amorphous H2O ice may also be present; the balance between the amorphization and crystallization processes on Charon remains to be clarified. The albedo of Charon and its generally spatially uniform neutral color indicate that a component, not yet identified, is mixed in some way with the H2O and NH3nH2O ices. Among the many known small bodies in the transneptunian region, several share characteristics with Pluto and Charon, including the presence of CH4, N2, C2H6, H2O ices, as well as components that yield a wide variety of surface albedo and color. The New Horizons investigation of the Pluto-Charon system will generate new insight into the physical properties of the broader transneptunian population, and eventually to the corresponding bodies expected in the numerous planetary systems currently being discovered elsewhere in the Galaxy.
Lunar surface composition and particle size, discussing lunar albedo and color data compatibility with rock compositions
A gradation of surface units represents either (1) an influx of basaltic sediment from southern highlands, deposited on andesitic volcanics, or (2) incompletely weathered basalt marking the geographic extent of submarine alteration of basaltic crust. Additional information is contained in the original extended abstract.
Results are presented from an AES investigation of the surface characteristics of pure Ti, Ti-14Al-21Nb (alpha-2 aluminide), and Ti-33Al-6Nb-1.4Ta (gamma aluminide) under ultrahigh vacuum conditions over the 20-1000 C temperature range. The observed variations in surface composition are noted to be dramatic and indicative of a direct relationship between the amount of retained oxygen and carbon on the surface and the quantity of Al in that surface's vicinity. While TiO2 was the main surface oxide for pure Ti and the alpha-2 and gamma aluminides, only metallic peaks were observable at 600 C; at 1000 C, metallic Al and Ti were observed.
The formation and growth processes of a bubble in the vicinity of graphite micro-fiber tips on metal-graphite composite boiling surfaces and their effects on boiling behavior are investigated. It is discovered that a large number of micro bubbles are formed first at the micro scratches and cavities on the metal matrix in pool boiling. By virtue of the non-wetting property of graphite, once the growing micro bubbles touch the graphite tips, the micro bubbles are sucked by the tips and merged into larger micro bubbles sitting on the end of the tips. The micro bubbles grow rapidly and coalesce to form macro bubbles, each spanning several tips. The necking process of a detaching macro bubble is analyzed. It is revealed that a liquid jet is produced by sudden break-off of the bubble throat. The composite surfaces not only have higher temperatures in micro- and macrolayers but also make higher frequency of the bubble departure, which increase the average heat fluxes in both the bubble growth stage and in the bubble departure period. Based on these analyses, the enhancement mechanism of pool boiling heat transfer on composite surfaces is clearly revealed.
Literature search of physical property data and composite surface work function models
Influence of time on vacuum vaporization rate and surface composition stability of tantalum carbide and hafnium carbide solid solutions above 2000 deg C
The paper investigates the bulk as well as near-surface composition of In(x)Ga(1-x)As epilayers on GaAs grown by chemical beam epitaxy (CBE) as a function of triethylindium flow rate and substrate temperature by reflection high energy electron diffraction (RHEED), X-ray diffraction, and XPS. To clarify whether the bulk stoichiometry of CBE-grown ternaries can be extracted from the growth rate change as determined by the change in the period of RHEED oscillations from binary to ternary compound growth, a systematic study of growth rate change as a function of ternary bulk composition determined by X-ray diffraction was performed at various temperatures. It is shown that for low growth temperatures there is a linear relationship between the two methods of determination, whereas no correlation is found for higher growth temperatures, in contrast to the MBE case where the two methods of determination yield identical results. In the near surface region the epilayer composition is determined in situ by XPS.
Both experimental and mechanism analysis studies about the enhanced pool boiling on the micro-configured composite surfaces have been conducted. The major study activities and results are summarized.
Using density functional theory, we find that tailoring the surface composition provides a route to stabilize the polar phases of the promising ferroelectric material, Hf x Zr 1-x O 2 . First, we show that for pure Hf O 2 , controlling the positively polarized surface to be relatively oxygen rich adequately screens the ferroelectric surface charges and stabilizes the polar orthorhombic phase. We then demonstrate that the ferroelectric polarization, as measured by the structural polar displacements, increases with decreasing thickness, leading to the emergence of a polar rhombohedral-like phase at the ultrathin limit (1.5 unit cells). Our findings extend to the cases of Hf 0.5 Zr 0.5 O 2 and Zr O 2 , both of which have surface energy landscapes similar to that of Hf O 2 . In conclusion, these findings are consistent with and offer insights into the observed absence of a ferroelectric thickness limit in Hf x Zr 1-x O 2 -based thin films.
The controversies surrounding the existing spectra of Mercury are discussed together with the various implications for interpretations of Mercury's surface composition. Special attention is given to the basic procedure used for reducing reflectance spectrophotometry data, the factors that must be accounted for in the reduction of these data, and the methodology for defining the portion of the surface contributing the greatest amount of light to an individual spectrum. The application of these methodologies to Mercury's spectra is presented.
A series of evolutionary models of 40-100 solar mass objects undergoing mass loss are constructed with the explicit inclusion of the surface composition of H, He, C, N, O elements. Mass loss rates similar to those observed in Of stars, 4 to 7 x 10 to the -6th solar masses/yr, result in an appearance at the surface of equilibrium CNO products, i.e. enhanced nitrogen and diminished carbon, while that star is still burning hydrogen in the core. This result obtains because the initial convection core is a relatively large fraction of the total mass and rather modest loss exposes levels of anomalous composition. It is suggested that these objects might reasonably be identified as those luminous late type WN stars still containing surface hydrogen.