Timing of Optical Maturation of Recently Exposed Material on Ceres

On Ceres, multispectral imaging data from the Dawn spacecraft show a distinct bluish characteristic for recently exposed material from the subsurface in, for example, crater ejecta. Ejecta blankets of presumably old craters show a more reddish spectrum. We selected areas in which fresh material from the Cerean subsurface was exposed at a specific time in the past, and no later geologic process is expected to have changed its surface composition or its cratering record. For each area, we determined two color ratios and the crater retention age. The measured color ratios show an exponential diminishment of the bluish characteristic over time. Although the cause of the color change remains uncertain, the time-dependent change in spectral properties is evident, which could help identify the process

Olivine or Impact Melt: Nature of the "Orange" Material on Vesta from Dawn

NASA's Dawn mission observed a great variety of colored terrains on asteroid (4) Vesta during its survey with the Framing Camera (FC). Here we present a detailed study of the orange material on Vesta, which was first observed in color ratio images obtained by the FC and presents a red spectral slope. The orange material deposits can be classified into three types, a) diffuse ejecta deposited by recent medium-size impact craters (such as Oppia), b) lobate patches with well-defined edges, and c) ejecta rays from fresh-looking impact craters. The location of the orange diffuse ejecta from Oppia corresponds to the olivine spot nicknamed "Leslie feature" first identified by Gaffey (1997) from ground-based spectral observations. The distribution of the orange material in the FC mosaic is concentrated on the equatorial region and almost exclusively outside the Rheasilvia basin. Our in-depth analysis of the composition of this material uses complementary observations from FC, the visible and infrared spectrometer (VIR), and the Gamma Ray and Neutron Detector (GRaND). Combining the interpretations from the topography, geomorphology, color and spectral parameters, and elemental abundances, the most probable analog for the orange material on Vesta is impact melt

Geologic mapping of the Urvara and Yalode Quadrangles of Ceres

We conducted geologic mapping of the Urvara (Ac-13) and Yalode (Ac-14) Quadrangles (21–66°S, 180–360°E) of the dwarf planet Ceres utilizing morphologic, topographic, and compositional information acquired by NASA's Dawn mission. The geologic characteristics of the two large impact basins Urvara (170 km diameter) and Yalode (260 km diameter) and their surroundings were investigated using Dawn Framing Camera datasets, including Survey (415 m/pixel), HAMO (140 m/pixel), and LAMO (35 m/pixel) images and mosaics, color and color ratio images, and DTMs derived from stereo-photogrammetry. Geologic mapping demonstrates that impact cratering has dominated the geologic history of the Urvara and Yalode Quadrangles, with early cratered terrain formation followed by formation of the large basins and widespread emplacement of basin-related smooth material. Impact craters display a wide range of preservation states from nearly completely buried/degraded forms to more recent pristine craters with terraced inner walls and lobate ejecta deposits. Cross-cutting relationships and morphologic signatures show that the Urvara impact followed the Yalode impact, consistent with ages derived from crater size-frequency distributions (580 ± 40 Ma for Yalode and 550 ± 50 Ma for Urvara). Observed differences in basin materials and rim morphology suggest heterogeneities in the substrate excavated by impact. Smooth deposits that cover large areas of the quadrangles, including the basin floors, rims, and exterior zones, are interpreted to be dominated by Urvara ejecta but Yalode ejecta and localized ice-rich flow material may be minor components. Geologic mapping results and simulations of ejecta emplacement suggest that Urvara and Yalode ejecta deposits extend for large distances (more than two crater diameters from the basin centers) and may serve as important stratigraphic markers for the geologic record of Ceres

Sustainable Management of Water Resources

The Dawn spacecraft arrived at dwarf planet Ceres in spring 2015 and imaged its surface from four successively lower polar orbits at ground sampling dimensions between ∼1.3 km/px and ∼35 m/px. To understand the geological history of Ceres a mapping campaign was initiated to produce a set of 15 quadrangle-based geological maps using the highest-resolution Framing Camera imagery. Here we present the geological map of the Ac-10 Rongo Quadrangle, which is located at the equator encompassing the region from 22°N to 22°S and 288° to 360°E. The total relief within the quadrangle is 11.1 km with altitudes ranging from about −7.3 km to +3.8 km. We identified nine geological units based on surface morphology and surface textural characteristics. The dominant and most widespread unit is the cratered terrain (crt) representing ancient reworked crustal material. Its consistent formation age across the quadrangle is 1.8 Ga. Two edifices (unit th), Ahuna Mons and an unnamed tholus within Begbalel Crater, are interpreted to be of (cryo)volcanic origin. The southwest portion of the quadrangle is dominated by ejecta material (Ye) emplaced during the formation of the 260-km diameter Yalode impact basin at about 580 Ma. Rayed crater ejecta material (cr) is dominant in the eastern part of the quadrangle but also occurs in isolated patches up to a distance of 455 km from the 34 km diameter source crater Haulani. The remaining five geological units also represent impact crater materials: degraded rim (crdeg), bright crater (cb), hummocky floor (cfh), talus (ta), and crater (c) materials. Widespread Yalode and Haulani ejecta materials can potentially be utilised as stratigraphic markers. Therefore, it is essential to consistently map their full areal extent and to date their formations using impact crater statistics