Extensive water ice within Ceres' aqueously altered regolith: Evidence from nuclear spectroscopy.

The surface elemental composition of dwarf planet Ceres constrains its regolith ice content, aqueous alteration processes, and interior evolution. Using nuclear spectroscopy data acquired by NASA's Dawn mission, we determined the concentrations of elemental hydrogen, iron, and potassium on Ceres. The data show that surface materials were processed by the action of water within the interior. The non-icy portion of Ceres' carbon-bearing regolith contains similar amounts of hydrogen to those present in aqueously altered carbonaceous chondrites; however, the concentration of iron on Ceres is lower than in the aforementioned chondrites. This allows for the possibility that Ceres experienced modest ice-rock fractionation, resulting in differences between surface and bulk composition. At mid-to-high latitudes, the regolith contains high concentrations of hydrogen, consistent with broad expanses of water ice, confirming theoretical predictions that ice can survive for billions of years just beneath the surface.

Distribution of phyllosilicates on the surface of Ceres.

The dwarf planet Ceres is known to host phyllosilicate minerals at its surface, but their distribution and origin have not previously been determined. We used the spectrometer onboard the Dawn spacecraft to map their spatial distribution on the basis of diagnostic absorption features in the visible and near-infrared spectral range (0.25 to 5.0 micrometers). We found that magnesium- and ammonium-bearing minerals are ubiquitous across the surface. Variations in the strength of the absorption features are spatially correlated and indicate considerable variability in the relative abundance of the phyllosilicates, although their composition is fairly uniform. These data, along with the distinctive spectral properties of Ceres relative to other asteroids and carbonaceous meteorites, indicate that the phyllosilicates were formed endogenously by a globally widespread and extensive alteration process.

Dawn arrives at Ceres: Exploration of a small, volatile-rich world.

On 6 March 2015, Dawn arrived at Ceres to find a dark, desiccated surface punctuated by small, bright areas. Parts of Ceres' surface are heavily cratered, but the largest expected craters are absent. Ceres appears gravitationally relaxed at only the longest wavelengths, implying a mechanically strong lithosphere with a weaker deep interior. Ceres' dry exterior displays hydroxylated silicates, including ammoniated clays of endogenous origin. The possibility of abundant volatiles at depth is supported by geomorphologic features such as flat crater floors with pits, lobate flows of materials, and a singular mountain that appears to be an extrusive cryovolcanic dome. On one occasion, Ceres temporarily interacted with the solar wind, producing a bow shock accelerating electrons to energies of tens of kilovolts.

Observations of comet 19P/Borrelly by the miniature integrated camera and spectrometer aboard Deep Space 1.

The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The 8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (

Orbiting stellar interferometer for astrometry and imaging.

The orbiting stellar interferometer (OSI) is a concept for a first-generation space interferometer with astrometric and imaging goals and is responsive to the recommendations of the Astronomy and Astrophysics Survey Committee for an astrometric interferometer mission. The OSI, as developed at the Jet Propulsion Laboratory over the past several years, is a triple Michelson interferometer with articulating siderostats and optical delay lines. Two point designs for the instrument are described.

The 18-m design uses an 18-m maximum baseline and aperture diameters of 40 cm; the targeted astrometric performance is a wide-field accuracy of 10 microarsec for 16-mag objects in 100 s of integration time and for 20-mag objects in 1 h. The instrument would also be capable of synthesis imaging with a resolution of 5 marcsec, which corresponds to the diffraction limit of the 18-m base line. The design uses a deployed structure, which would fold to fit into an Atlas HAS shroud, for insertion into a 900-km sun-synchronous orbit In addition to the 18-m point design a 7-m point design that uses a shorter base line in order to simplify deployment is also discussed. OSI's high performance is made possible by utilizing laser metrology and controlled-optics technology.