Carbonaceous chondrites as analogs for the composition and alteration of Ceres

The mineralogy and geochemistry of Ceres, as constrained by Dawn's instruments, are broadly consistent with a carbonaceous chondrite (CM/CI) bulk composition. Differences explainable by Ceres’s more advanced alteration include the formation of Mg‐rich serpentine and ammoniated clay; a greater proportion of carbonate and lesser organic matter; amounts of magnetite, sulfide, and carbon that could act as spectral darkening agents; and partial fractionation of water ice and silicates in the interior and regolith. Ceres is not spectrally unique, but is similar to a few other C‐class asteroids, which may also have suffered extensive alteration. All these bodies are among the largest carbonaceous chondrite asteroids, and they orbit in the same part of the Main Belt. Thus, the degree of alteration is apparently related to the size of the body. Although the ammonia now incorporated into clay likely condensed in the outer nebula, we cannot presently determine whether Ceres itself formed in the outer solar system and migrated inward or was assembled within the Main Belt, along with other carbonaceous chondrite bodies.     

Mineralogy and temperature of crater Haulani on Ceres

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH₄‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na₂CO₃ may be still ongoing.     

Lunar surface agglutinates: Mapping composition anomalies

From the Clementine UVVIS imagery of the lunar surface, the abundance of agglutinates in the lunar regolith and their composition in terms of FeO and Al₂O₃ oxides have been predicted. Data on the spectral, chemical, and mineralogic measurements of about 30 lunar soil samples from the Lunar Samples Characterization Consortium (LSCC) collection were used. The fulfilled prognosis confirms that the mare agglutinates are enriched in Al₂O₃ and depleted of FeO, while the highland agglutinates are depleted of Al₂O₃ and enriched in FeO. This behavior can be caused by the global transport of the lunar surface material induced by cosmogenic factors.     

Evidence of space weathering in regolith breccias I: Lunar regolith breccias

Abstract— We have analyzed a suite of lunar regolith breccias in order to assess how well space weathering products can be preserved through the lithification process and therefore whether or not it is appropriate to search for space weathering products in asteroidal regolith breccia meteorites. It was found that space weathering products, vapor/sputter deposited nanophase‐iron‐bearing rims in particular, are easily identified in even heavily shocked/compacted lunar regolith breccias. Such rims, if created on asteroids, should thus be preserved in asteroidal regolith breccia meteorites. Two additional rim types, glass rims and vesicular rims, identified in regolith breccias, are also described. These rims are common in lunar regolith breccias but rare to absent in lunar soils, which suggests that they are created in the breccia‐forming process itself. While not “space weathering products” in the strictest sense, these additional rims give us insight into the regolith breccia formation process. The presence or absence of glass and/or vesicular rims in asteroidal regolith breccias will likewise tell us about environmental conditions on the surface of the asteroid body on which the breccia was created.     

Spectral properties of simulated impact glasses produced from martian soil analogue JSC Mars-1

To simulate the formation of impact glasses on Mars, an analogue of martian bright soil (altered volcanic soil JSC Mars-1) was melted at relevant oxygen fugacities using a pulsed laser and a resistance furnace. Reduction of Fe³⁺ to Fe²⁺ and in some cases formation of nanophase Fe⁰ in the glasses were documented by Mössbauer spectroscopy and TEM studies. Reflectance spectra for several size fractions of the JSC Mars-1 sample and the glasses were acquired between 0.3 and 25 μm. The glasses produced from the JSC Mars-1 soil show significant spectral variability depending on the method of production and the cooling rate. In general, they are dark and less red in the visible compared to the original JSC Mars-1 soil. Their spectra do not have absorption bands due to bound water and structural OH, have positive spectral slopes in the near-infrared range, and show two broad bands centered near 1.05 and 1.9 μm, typical of glasses rich in ferrous iron. The latter bands and low albedo partly mimic the spectral properties of martian dark regions, and may easily be confused with mafic materials containing olivine and low-Ca pyroxene. Due to their disordered structures and vesicular textures, the glasses show relatively weak absorption features from the visible to the thermal infrared. These weak absorption bands may be masked by the stronger bands of mafic minerals. Positive near-infrared spectral slopes typical of fresh iron-bearing impact or volcanic glasses may be masked either by oxide/dust coatings or by aerosols in the Mars' atmosphere. As a result, impact glasses may be present on the surface of Mars in significant quantities that have been either misidentified as other phases or masked by phases with stronger infrared features. Spectrometers with sufficient spatial resolution and wavelength coverage may detect impact glasses at certain locations, e.g., in the vicinity of fresh impact craters. Such dark materials are usually interpreted as accumulations of mafic volcanic sand, but the possibility of an impact melt origin of such materials also should be considered. In addition, our data suggest that high contents of feldspars or zeolites are not necessary to produce the transparency feature at 12.1 μm typical of martian dust spectra.     

Dawn Mission to Vesta and Ceres

The initial exploration of any planetary object requires a careful mission design guided by our knowledge of that object as gained by terrestrial observers. This process is very evident in the development of the Dawn mission to the minor planets 1 Ceres and 4 Vesta. This mission was designed to verify the basaltic nature of Vesta inferred both from its reflectance spectrum and from the composition of the howardite, eucrite and diogenite meteorites believed to have originated on Vesta. Hubble Space Telescope observations have determined Vesta’s size and shape, which, together with masses inferred from gravitational perturbations, have provided estimates of its density. These investigations have enabled the Dawn team to choose the appropriate instrumentation and to design its orbital operations at Vesta. Until recently Ceres has remained more of an enigma. Adaptive-optics and HST observations now have provided data from which we can begin to confidently plan the mission. These observations reveal a rotationally symmetric body with little surface relief, an ultraviolet bright point that can be used as a control point for determining the pole and anchoring a geographic coordinate system. They also reveal albedo and color variations that provide tantalizing hints of surface processes.     

Definition and detailed characterization of Lunar surface units using remote observations

Remote sensing techniques and data may be subdivided into three principal types according to how they are used: (1) defining techniques help to define unit boundaries and extent; (2) characterizing techniques allow classification and characterization of physical features, lithology, or chemical composition; (3) supporting techniques provide additional useful information but are not fundamental to the definition or characterization of units. Defined units represent a fundamental subdivision of the rocks in a planetary crust and thus represent processes and sequences of events. The definition and characterization of units provides a framework for the interpretation of planetary processes and history. Detailed consideration of unit definition and characterization is presented using the mare deposits of the Imbrium basin as an example. This example provides guidelines for the utilization of remote sensing techniques in geologic mapping of the Moon and other planets.     

Climate change and population history in the Pacific Lowlands of Southern Mesoamerica

Core MAN015 from Pacific coastal Guatemala contains sediments accumulated in a mangrove setting over the past 6500 yr. Chemical, pollen, and phytolith data, which indicate conditions of estuarine deposition and terrigenous inputs from adjacent dry land, document Holocene climate variability that parallels the Maya lowlands and other New World tropical locations. Human population history in this region may be driven partly by climate variation: sedentary human populations spread rapidly through the estuarine zone of the lower coast during a dry and variable 4th millennium B.P. Population growth and cultural florescence during a long, relatively moist period (2800–1200 B.P.) ended around 1200 B.P., a drying event that coincided with the Classic Maya collapse.     

Spectroscopy of Yamato 984028

Comprehensive spectroscopic characterization of interior and exterior chips of the lherzolitic shergottite Y-984028 has been performed using results from six techniques. Data from UV–visible–near-IR reflectance spectra, thermal (mid-IR) emission spectra, attenuated total reflectance (ATR) spectra, transmission FTIR spectra, Raman microprobe spectra, and Mössbauer spectra of whole rock and mineral separates from this meteorite are integrated and compared. Five of these analytical techniques accurately determined the ～Fo₆₅ composition of the olivine within ±10 mol%. Both transmission FTIR and ATR spectra show broad features near 3500 cm^?1 indicating the presence of OH/H₂O that does not arise from surface water adsorption. The brown color of the Y-984028 olivine is likely due to the presence of nanophase metallic iron particles (npFe⁰) dispersed throughout the olivine during a major shock event on Mars. Y-984028 olivine also contains a significant amount of Fe³⁺, but this cannot be distinguished from Fe³⁺ that is present in pyroxene and possibly clay minerals. This meteorite and the nakhlite MIL03346 are the two most oxidized of the SNC meteorites studied to date, with Fe³⁺ contents consistent with high-temperature equilibration near the QFM oxygen buffer.