69 research outputs found
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
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
Mapping Vesta: First Results from Dawn’s Survey Orbit
The geologic objectives of the Dawn Mission [1] are
to derive Vesta’s shape, map the surface geology,
understand the geological context and contribute to
the determination of the asteroids’ origin and
evolution.Geomorphology and distribution of surface features
will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral
measurements of the surface will provide evidence of
the compositional characteristics of geological units.
Age information, as derived from crater sizefrequency
distributions, provides the stratigraphic
context for the structural and compositional mapping
results, thus revealing the geologic history of Vesta.
We present here the first results of the Dawn mission
from data collected during the approach to Vesta, and
its first discrete orbit phase – the Survey Orbit, which
lasts 21 days after the spacecraft had established a
circular polar orbit at a radius of ~3000 km with a
beta angle of 10°-15°
Mass Movement on Vesta at Steep Scarps and Crater Rims
The Quadrangles Av-11 and Av-12 on Vesta are located at the northern rim of the giant Rheasilvia south polar impact basin. The primary geologic units in Av-11 and Av-12 include material from the Rheasilvia impact basin formation, smooth material and different types of impact crater structures (such as bimodal craters, dark and bright crater ray material and dark ejecta material). Av-11 and Av-12 exhibit almost the full range of mass wasting features observed on Vesta, such as slump blocks, spur-and-gully morphologies and landslides within craters. Processes of collapse, slope instability and seismically triggered events force material to slump down crater walls or scarps and produce landslides or rotational slump blocks. The spur-and-gully morphology that is known to form on Mars is also observed on Vesta; however, on Vesta this morphology formed under dry conditions
Regolith Depth, Mobility, and Variability on Vesta from Dawn's Low Altitude Mapping Orbit
Regolith, the fragmental debris layer formed from impact events of all sizes, covers the surface of all asteroids imaged by spacecraft to date. Here we use Framing Camera (FC) images [1] acquired by the Dawn spacecraft [2] from its low-altitude mapping orbit (LAMO) of 210 km (pixel scales of ~20 m) to characterize regolith depth, variability, and mobility on Vesta, and to locate areas of especially thin regolith and exposures of competent material. These results will help to evaluate how the surface of this differentiated asteroid has evolved over time, and provide key contextual information for understanding the origin and degree of mixing of the surficial materials for which compositions are estimated [3,4] and the causes of the relative spectral immaturity of the surface [5]. Vestan regolith samples, in the form of howardite meteorites, can be studied in the laboratory to provide complementary constraints on the regolith process [6]
Nature of the "Orange" Material on Vesta From Dawn
From ground-based observations of Vesta, it is well-known that the vestan surface has a large variation in albedo. Analysis of images acquired by the Hubble Space Telescope allowed production of the first color maps of Vesta and showed a diverse surface in terms of reflectance. Thanks to images collected by the Dawn spacecraft at Vesta, it became obvious that these specific units observed previously can be linked to geological features. The presence of the darkest material mostly around impact craters and scattered in the Western hemisphere has been associated with carbonaceous chondrite contamination [4]; whereas the brightest materials are believed to result from exposure of unaltered material from the subsurface of Vesta (in fresh looking impact crater rims and in Rheasilvia's ejecta and rim remants). Here we focus on a distinct material characterized by a steep slope in the near-IR relative to all other kinds of materials found on Vesta. It was first detected when combining Dawn Framing Camera (FC) color images in Clementine false-color composites [5] during the Approach phase of the mission (100000 to 5200 km from Vesta). We investigate the mineralogical and elemental composition of this material and its relationship with the HEDs (Howardite-Eucrite- Diogenite group of meteorites)
Evidence for the Interior Evolution of Ceres from Geologic Analysis of Fractures
Ceres is the largest asteroid belt object, and the Dawn spacecraft observed Ceres since 2015.
Dawn observed two morphologically distinct linear features on Ceres’s surface: secondary crater chains
and pit chains. Pit chains provide unique insights into Ceres’s interior evolution. We interpret pit chains called
the Samhain Catenae as the surface expression of subsurface fractures. Using the pit chains’ spacings, we
estimate that the localized thickness of Ceres’s fractured, outer layer is approximately ≥58 km, at least ~14 km
greater than the global average. We hypothesize that extensional stresses, induced by a region of upwelling
material arising from convection/diapirism, formed the Samhain Catenae. We derive characteristics for this
upwelling material, which can be used as constraints in future interior modeling studies. For example, its
predicted location coincides with Hanami Planum, a high-elevation region with a negative residual gravity
anomaly, which may be surficial evidence for this proposed region of upwelling material
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