Engineering topics

Schroder, S. E.

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

6 records

NASA NTRS2018

Dawn Mission's Search for Satellites of Ceres: Intact Protoplanets Don't Have Satellites

Upon its approach to orbit the dwarf planet Ceres in early 2015, optical navigation and dedicated satellite search images were acquired with the Dawn mission's framing camera 2. A team of searchers individually processed and examined the images for evidence of objects moving with Ceres. Completeness of search with respect to the space searched was calculated as a function of distance to Ceres and found to be complete down to 15 Ceres radii (Ceres' mean radius is 470 kilometers). Upper limits of detectable magnitude were determined for each observed set of images and an upper limit in size was calculated assuming for the putative objects, Ceres' geometric albedo of 0.11. Nothing was found associated with Ceres down to a radius of 12 meters for the most sensitive search, and down to a radius of 323m for the least sensitive search circumstances. Examination of the physical properties of the 41 largest and most massive main belt asteroids suggests that large asteroids without satellites are intact and their interiors have internal strength. This is consistent with results from the Dawn mission at both Vesta and Ceres. Ceres' volatile-rich composition also is a likely contributor to both the absence of satellites at Ceres and of Ceres meteorites at Earth. These results suggest that collisional disruption creating rubble pile structure is a necessary condition for formation of satellites around main belt asteroids.

McFadden, Lucy A.↗

NASA NTRS2017

Boulders on Ceres

Introduction: In December 2015 the Dawn spacecraft moved into the Low Altitude Mapping Orbit (LAMO) around Ceres, encircling the dwarf planet at a distance of 400 km to the surface below. At this altitude, images of the on-board framing camera have a resolution of 36 meters per pixel, high enough to distinguish large boulders on the surface. Indeed, LAMO images show a multitude of boulders around what seem to be fresh craters. The average life-time of boulders on Dawn's previous target, Vesta, was estimated to be similar to that of Lunar boulders, as may be expected from the basaltic surface composition. The bulk composition of Ceres may be carbonaceous chondrite-like with significant contributions of clays, salt, and water ice. As such, the abundance and distribution of boulders on Ceres may be different from that on Vesta. We mapped, counted, and measured the diameter of boulders over the entire surface of Ceres. Our analysis of the data in combination with crater age estimates may provide clues to the physical nature and composition of the surface.

Ceres↗

NASA NTRS2017

Ceres Obliquity History and Its Implications for the Permanently Shadowed Regions

Due to the small current obliquity of Ceres ( epsilon approximately equal to 4), permanently shadowed regions (PSRs) exist on the dwarf planets surface. Since the existence and persistence of the PSRs depend on the obliquity, we compute the obliquity history over the last 3 My and find that it undergoes large oscillations with a period of 24.5 ky and a maximum of max 19:5. During periods of large obliquity, most of the present-day PSRs receive direct sunlight. Some craters in Ceres polar regions possess bright crater floor deposits (BCFDs).We find an apparent correlation between BCFDs and the most persistent PSRs. In the north, only two PSRs remain at max and they both contain BCFDs. In the south, one of the two only craters that remain in shadow at max contains a BCFD. The location of BCFDs within persistent PSRs strongly suggests BCFDs consist of volatiles accumulated in PSR cold traps: either water molecules trapped from the exosphere or exposed ground ice.

Ermakov, A. I.↗

NASA NTRS2012

Types and Distribution of Bright Materials in 4 Vesta

A strong case can be made that Vesta is the parent asteroid of the howardite, eucrite and diogenite (HED) meteorites [1]. As such, we have over a century of detailed sample analysis experience to call upon when formulating hypotheses regarding plausible lithologic diversity on Vesta. It thus came as a surprise when Dawn s Framing Camera (FC) first revealed distinctly localized materials of exceptionally low and high albedos, often closely associated. To understand the nature and origin of these materials, and how they inform us of the geological evolution of Vesta, task forces began their study. An initial step of the scientific endeavor is to develop a descriptive, non-genetic classification of objects to use as a basis for developing hypotheses and observational campaigns. Here we present a catalog of the types of light-toned deposits and their distribution across Vesta. A companion abstract [2] discusses possible origins of bright materials and the constraints they suggest for vestan geology.

Mittlefehldt, D. W.↗

NASA NTRS2012

Visible Color and Photometry of Bright Materials on Vesta

The Dawn Framing Camera (FC) collected images of the surface of Vesta at a pixel scale of ~70 m in the High Altitude Mapping Orbit (HAMO) phase through its clear and seven color filters spanning from 430 nm to 980 nm. The surface of Vesta displays a large diversity in its brightness and colors, evidently related to the diverse geology [1] and mineralogy [2]. Here we report a detailed investigation of the visible colors and photometric properties of the apparently bright materials on Vesta in order to study their origin. The global distribution and the spectroscopy of bright materials are discussed in companion papers [3, 4], and the synthesis results about the origin of Vestan bright materials are reported in [5].

Schroder, S. E.↗

NASA NTRS2012

Investigating the Origin of Bright Materials on Vesta: Synthesis, Conclusions, and Implications

The Dawn spacecraft started orbiting the second largest asteroid (4) Vesta in August 2011, revealing the details of its surface at an unprecedented pixel scale as small as approx.70 m in Framing Camera (FC) clear and color filter images and approx.180 m in the Visible and Infrared Spectrometer (VIR) data in its first two science orbits, the Survey Orbit and the High Altitude Mapping Orbit (HAMO) [1]. The surface of Vesta displays the greatest diversity in terms of geology and mineralogy of all asteroids studied in detail [2, 3]. While the albedo of Vesta of approx.0.38 in the visible wavelengths [4, 5] is one of the highest among all asteroids, the surface of Vesta shows the largest variation of albedos found on a single asteroid, with geometric albedos ranging at least from approx.0.10 to approx.0.67 in HAMO images [5]. There are many distinctively bright and dark areas observed on Vesta, associated with various geological features and showing remarkably different forms. Here we report our initial attempt to understand the origin of the areas that are distinctively brighter than their surroundings. The dark materials on Vesta clearly are different in origin from bright materials and are reported in a companion paper [6].

Li, Jian-Yang↗