Engineering topics

Schroeder, S. E.

Publications and source records attributed to Schroeder, S. E..

6 records

NASA NTRS2016

Surface Water-Ice Deposits in the Northern Shadowed Regions of Ceres

Ceres, a dwarf planet located in the main asteroid belt, has a low bulk density, and models predict that a substantial amount of water ice is present in its mantle and outer shell. The Herschel telescope and the Dawn spacecraft have observed the release of water vapor from Ceres, and exposed water ice has been detected by Dawn on its surface at mid-latitudes. Water molecules from endogenic and exogenic sources can also be cold-trapped in permanent shadows at high latitudes, as happens on the Moon and Mercury. Here we present the first image-based survey of Ceres's northern permanent shadows and report the discovery of bright deposits in cold traps. We identify a minimum of 634 permanently shadowed craters. Bright deposits are detected on the floors of just 10 of these craters in multiscattered light. We spectroscopically identify one of the bright deposits as water ice. This detection strengthens the evidence that permanently shadowed areas have preserved water ice on airless planetary bodies.

Surface Water↗

NASA NTRS2013

Mineralogical Composition of the Different Types of Bright Deposits on Vesta

VIR-MS, Dawn's Visible and Infrared Mapping Spectrometer, obtained hyperspectral images of a wide part of Vesta's surface at a variety of spatial resolutions [1]. Vesta spectra are similar to those of the howardite-eucrite-diogenite (HED) meteorites. Moreover, they are characterized by the two iron-bearing pyroxene bands at 0.9 (band I) and 1.9 microns (band II). Vesta surface's is dominated by eucrite/howardite with some diogenitic regions situated in the southern hemisphere near the Rheasilvia basin [2]. The surface is heavily craterized and impacts can expose fresh material, thus generating the Bright Material Deposits (BMD) observed within and surrounding certain craters. BMD can be classified into six different types based on their morphological characteristics: Crater Wall/Scarp Material (CWM), Radial Material (RM), Slope Material (SM), Patchy Material (PM), Spot Material (SpM) and Diffuse Plains Material (DPM) [3]. The most widespread BMD are CWM, SM and RM. CWM, SM, RM originate from impacts. CWM is situated on the edge of the craters. Mass wasting from the crater walls and generates the SM, while RM is associated with the ejecta of the craters [4]. BMD are characterized by albedo greater than that of the vestan average, 0.38 [5]. Therefore the different types of deposits present distinct levels of reflectance respect to the Surrounding Regions (SR), in particular: the CWM and SM is approx.40% brighter, the RM is approx.30- 40% brighter; the SpM is about 20-25% brighter and the PM is about 20% brighter. Near the edge of the Rheasilvia basin it is possible to find some extremely bright areas ~80% brighter than the vestan average [6].

Zambon, F.↗

NASA NTRS2012

Geologic Structures in Crater Walls on Vesta

The Framing Camera (FC) on the Dawn spacecraft has imaged most of the illuminated surface of Vesta with a resolution of apporpx. 20 m/pixel through different wavelength filters that allow for identification of lithologic units. The Visible and Infrared Mapping Spectrometer (VIR) has imaged the surface at lower spatial resolution but high spectral resolution from 0.25 to 5 micron that allows for detailed mineralogical interpretation. The FC has imaged geologic structures in the walls of fresh craters and on scarps on the margin of the Rheasilvia basin that consist of cliff-forming, competent units, either as blocks or semi-continuous layers, hundreds of m to km below the rims. Different units have different albedos, FC color ratios and VIR spectral characteristics, and different units can be juxtaposed in individual craters. We will describe different examples of these competent units and present preliminary interpretations of the structures. A common occurrence is of blocks several hundred m in size of high albedo (bright) and low albedo (dark) materials protruding from crater walls. In many examples, dark material deposits lie below coherent bright material blocks. In FC Clementine color ratios, bright material is green indicating deeper 1 m pyroxene absorption band. VIR spectra show these to have deeper and wider 1 and 2 micron pyroxene absorption bands than the average vestan surface. The associated dark material has subdued pyroxene absorption features compared to the average vestan surface. Some dark material deposits are consistent with mixtures of HED materials with carbonaceous chondrites. This would indicate that some dark material deposits in crater walls are megabreccia blocks. The same would hold for bright material blocks found above them. Thus, these are not intact crustal units. Marcia crater is atypical in that the dark material forms a semi-continuous, thin layer immediately below bright material. Bright material occurs as one or more layers. In one region, there is an apparent angular unconformity between the bright material and the dark material where bright material layers appear to be truncated against the underlying dark layer. One crater within the Rheasilvia basin contains two distinct types of bright materials outcropping on its walls, one like that found elsewhere on Vesta and the other an anomalous block ~200 m across. This material has the highest albedo; almost twice that of the vestan average. Unlike all other bright materials, this block has a subdued 1 micron pyroxene absorption band in FC color ratios. These data indicate that this block represents a distinct vestan lithology that is rarely exposed.

Mittlefehldt, David W.↗

NASA NTRS2012

Spectral Characterization of Bright Materials on Vesta

The surface of Vesta, as observed by the camera and imaging spectrometer onboard the Dawn spacecraft, displays large surface diversity in terms of its geology and mineralogy with noticeably dark and bright areas on the surface often associated with various geological features and showing remarkably different forms. Here we report our initial attempt to spectrally characterize the areas that are distinctively brighter than their surroundings.

Capaccioni, Fabrizio↗

NASA NTRS2012

Colors and Photometry of Bright Materials on Vesta as Seen by the Dawn Framing Camera

The Dawn spacecraft has been in orbit around the asteroid Vesta since July, 2011. The on-board Framing Camera has acquired thousands of high-resolution images of the regolith-covered surface through one clear and seven narrow-band filters in the visible and near-IR wavelength range. It has observed bright and dark materials that have a range of reflectance that is unusually wide for an asteroid. Material brighter than average is predominantly found on crater walls, and in ejecta surrounding caters in the southern hemisphere. Most likely, the brightest material identified on the Vesta surface so far is located on the inside of a crater at 64.27deg S, 1.54deg . The apparent brightness of a regolith is influenced by factors such as particle size, mineralogical composition, and viewing geometry. As such, the presence of bright material can indicate differences in lithology and/or degree of space weathering. We retrieve the spectral and photometric properties of various bright terrains from false-color images acquired in the High Altitude Mapping Orbit (HAMO). We find that most bright material has a deeper 1-m pyroxene band than average. However, the aforementioned brightest material appears to have a 1-m band that is actually less deep, a result that awaits confirmation by the on-board VIR spectrometer. This site may harbor a class of material unique for Vesta. We discuss the implications of our spectral findings for the origin of bright materials.

Schroeder, S. E.↗

NASA NTRS2011

4 Vesta in Color: High Resolution Mapping from Dawn Framing Camera Images

Rotational surface variations on asteroid 4 Vesta have been known from ground-based and HST observations, and they have been interpreted as evidence of compositional diversity. NASA s Dawn mission entered orbit around Vesta on July 16, 2011 for a year-long global characterization. The framing cameras (FC) onboard the Dawn spacecraft will image the asteroid in one clear (broad) and seven narrow band filters covering the wavelength range between 0.4-1.0 microns. We present color mapping results from the Dawn FC observations of Vesta obtained during Survey orbit (approx.3000 km) and High-Altitude Mapping Orbit (HAMO) (approx.950 km). Our aim is to create global color maps of Vesta using multi spectral FC images to identify the spatial extent of compositional units and link them with other available data sets to extract the basic mineralogy. While the VIR spectrometer onboard Dawn has higher spectral resolution (864 channels) allowing precise mineralogical assessment of Vesta s surface, the FC has three times higher spatial resolution in any given orbital phase. In an effort to extract maximum information from FC data we have developed algorithms using laboratory spectra of pyroxenes and HED meteorites to derive parameters associated with the 1-micron absorption band wing. These parameters will help map the global distribution of compositionally related units on Vesta s surface. Interpretation of these units will involve the integration of FC and VIR data.

Reddy, V.↗