Search

The typically dark surface of the dwarf planet Ceres is punctuated by areas of much higher albedo, most prominently in the Occator crater (1). These small bright areas have been tentatively interpreted as containing a large amount of hydrated magnesium sulfate (1), in contrast to the average surface, which is a mixture of low-albedo materials and magnesium phyllosilicates, ammoniated phyllosilicates and carbonates (2-4). Here we report high spatial and spectral resolution near-infrared observations of the bright areas in the Occator crater on Ceres. Spectra of these bright areas are consistent with a large amount of sodium carbonate, constituting the most concentrated known extraterrestrial occurrence of carbonate on kilometre-wide scales in the Solar System. The carbonates are mixed with a dark component and small amounts of phyllosilicates, as well as ammonium carbonate or ammonium chloride. Some of these compounds have also been detected in the plume of Saturn's sixth-largest moon Enceladus (5). The compounds are endogenous and we propose that they are the solid residue of crystallization of brines and entrained altered solids that reached the surface from below. The heat source may have been transient (triggered by impact heating). Alternatively, internal temperatures may be above the eutectic temperature of subsurface brines, in which case fluids may exist at depth on Ceres today., Occator is a prominent, geologically young crater (1,6) (diameter ~90 km, 19.4° N, 239.0° E), and its brightest region (Fig. 1) is at the centre of the crater, close to [...]

Studies of the dwarf planet (1) Ceres using ground-based and orbiting telescopes have concluded that its closest meteoritic analogues are the volatile-rich CI and CM carbonaceous chondrites (1, 2). Water in clay minerals (3), ammoniated phyllosilicates (4), or a mixture of Mg[(OH).sub.2] (brucite), [Mg.sub.2]C[O.sub.3] and iron-rich serpentine (5, 6) have all been proposed to exist on the surface. In particular, brucite has been suggested from analysis of the mid-infrared spectrum of Ceres (6). But the lack of spectral data across telluric absorption bands in the wavelength region 2.5 to 2.9 micrometres--where the OH stretching vibration and the [H.sub.2]O bending overtone are found--has precluded definitive identifications. In addition, water vapour around Ceres has recently been reported (7), possibly originating from localized sources. Here we report spectra of Ceres from 0.4 to 5 micrometres acquired at distances from ~82,000 to 4,300 kilometres from the surface. Our measurements indicate widespread ammoniated phyllosilicates across the surface, but no detectable water ice. Ammonia, accreted either as organic matter or as ice, may have reacted with phyllosilicates on Ceres during differentiation. This suggests that material from the outer Solar System was incorporated into Ceres, either during its formation at great heliocentric distance or by incorporation of material transported into the main asteroid belt., The Visible-Infrared Mapping Spectrometer VIR (8) on the Dawn spacecraft (9) obtained multi-spectral images of Ceres' surface in the spectral range 0.4-5 µm with an instantaneous field of view of [...]

The dwarf planet (1) Ceres, the largest object in the main asteroid belt (1) with a mean diameter of about 950 kilometres, is located at a mean distance from the Sun of about 2.8 astronomical units (one astronomical unit is the Earth-Sun distance). Thermal evolution models suggest that it is a differentiated body with potential geological activity (2,3). Unlike on the icy satellites of Jupiter and Saturn, where tidal forces are responsible for spewing briny water into space, no tidal forces are acting on Ceres. In the absence of such forces, most objects in the main asteroid belt are expected to be geologically inert. The recent discovery (4) of water vapour absorption near Ceres and previous detection of bound water and OH near and on Ceres (refs 5-7) have raised interest in the possible presence of surface ice. Here we report the presence of localized bright areas on Ceres from an orbiting imager (8). These unusual areas are consistent with hydrated magnesium sulfates mixed with dark background material, although other compositions are possible. Of particular interest is a bright pit on the floor of crater Occator that exhibits probable sublimation of water ice, producing haze clouds inside the crater that appear and disappear with a diurnal rhythm. Slow-moving condensed-ice or dust particles (9,10) may explain this haze. We conclude that Ceres must have accreted material from beyond the 'snow line' (11), which is the distance from the Sun at which water molecules condense., We observed Ceres using the Framing Camera (FC) on board the Dawn spacecraft. The FC is equipped with a panchromatic (clear) filter and seven colour filters, covering the wavelength range [...]

Olivine is a major component of the mantle of differentiated bodies, including Earth. Howardite, eucrite and diogenite (HED) meteorites represent regolith, basaltic-crust, lower-crust and possibly ultramafic-mantle samples of asteroid Vesta, which is the lone surviving, large, differentiated, basaltic rocky protoplanet in the Solar System (1). Only a few of these meteorites, the orthopyroxene-rich diogenites, contain olivine, typically with a concentration of less than 25 per cent by volume (2). Olivine was tentatively identified on Vesta (3,4), on the basis of spectral and colour data, but other observations did not confirm its presence (5). Here we report that olivine is indeed present locally on Vesta's surface but that, unexpectedly, it has not been found within the deep, south-pole basins, which are thought to be excavated mantle rocks (6-8). Instead, it occurs as near-surface materials in the northern hemisphere. Unlike the meteorites, the olivine-rich (more than 50 per cent by volume) material is not associated with diogenite but seems to be mixed with howardite, the most common (7,9) surface material. Olivine is exposed in crater walls and in ejecta scattered diffusely over a broad area. The size of the olivine exposures and the absence of associated diogenite favour a mantle source, but the exposures are located far from the deep impact basins. The amount and distribution of observed olivine-rich material suggest a complex evolutionary history for Vesta., The Visible and Infrared Mapping Spectrometer (VIR) on board NASA's Dawn spacecraft (10) has been used in a global search for olivine on the Vestan surface (Supplementary Information). VIR revealed [...]

The surface of the asteroid Vesta has prominent near-infrared absorption bands characteristic of a range of pyroxenes, confirming a direct link to the basaltic howardite-eucrite-diogenite class of meteorites (1,2,3). Processes [...]

The search for water on the surface of the anhydrous Moon had remained an unfulfilled quest for 40 years. However, the Moon Mineralogy Mapper ([M.sup.3]) on Chandrayaan-1 has recently detected absorption features near 2.8 to 3.0 micrometers on the surface of the Moon. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit [M.sup.3] data with neutron spectrometer hydrogen abundance data suggests that the formation and retention of hydroxyl and water are ongoing surficial processes. Hydroxyl/water production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration. 10.1126/science.1178658

Laboratory results from a simulation of possible optical effects of impact melting and repeated crystallization on asteroidal surfaces are presented. Quick melting and crystallization of surface materials were simulated by impulse laser treatment of powdered materials in vacuum. The mafic materials used in this study were: ordinary chondrite (OC) Elenovka L5, carbonaceous chondrite Allende CV3, terrestrial olivine, clinopyroxene, and olivine-clinopyroxene mixture 1:1. The reflectance spectra of powdered samples before and after laser treatment were recorded in the range 0.3-25 [[micro]meter]. The laboratory laser alteration produced a reduction in overall reflectance and spectral contrast, a noticeable increase in spectral slope, the shifts in the wavelength positions of absorption band centers, and a decrease in band area ratio. The continuum slope of the ordinary chondrite Elenovka after laser treatment is comparable to that of S-type asteroids. Laser impulse alteration raises the spectrally derived olivine/orthopyroxene ratio of Elenovka from 2.8 to 5.4. This value is far outside the OC range, but falls within the olivine/orthopyroxene range for S-asteroids. The results suggest that quick melting and subsequent crystallization can enhance the spectral similarity between S-asteroids and ordinary chondrites.

The ultraviolet-visible camera on the Clementine spacecraft obtained high-spatial resolution images of the moon in five spectral channels. impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy. Prominent lithologic variations feldspathic versus basaltic) occur within the south wall of Copemicus (93 kilometers in diameter) on the scale of 1 to 2 kilometers. Lithologic diversity at Tycho (85 kilometers in diameter) is less apparent at this scale, although the impact melt of these two large craters is remarkably similar in this spectral range. The lunar surface within and around the smaller crater Giordano Bruno (22 kilometers in diameter) is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology., The Clementine spacecraft acquired digital images of the lunar surface using four co-aligned framing cameras sensitive to radiation from the visible to mid-infrared (1). Preliminary results derived from processed data [...]

In the course of 71 days in lunar orbit, from 19 February to 3 May 1994, the Clementine spacecraft acquired just under two million digital images of the moon at visible and infrared wavelengths. These data are enabling the global mapping of the rock types of the lunar crust and the first detailed investigation of the geology of the lunar polar regions and the lunar far side. In addition, laser-ranging measurements provided the first view of the global topographic figure of the moon. The topography of many ancient impact basins has been measured, and a global map of the thickness of the lunar crust has been derived from the topography and gravity., In early 1992, after a 4-month effort by the National Aeronautics and Space Administration (NASA), the U.S. Department of Defense, and industry, it was concluded that a mission to a [...]