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  • 1
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    Dawn Mission's Search for Satellites of Ceres: Intact Protoplanets Don't Have Satellites (2018)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: 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.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN68836 , Icarus (ISSN 0019-1035) (e-ISSN 1090-2643); 316; 191-204
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  • 2
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    The Nucleus of Comet 9P-Tempel 1: Shape and Geology from Two Flybys (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The nucleus of comet Tempel 1 has been investigated at close range during two spacecraft missions separated by one comet orbit of the Sun, 5 1/2 years. The combined imaging covers 70% of the surface of this object which has a mean radius of 2.83 +/- 0.1 km. The surface can be divided into two terrain types: rough, pitted terrain and smoother regions of varying local topography. The rough surface has round depressions from resolution limits (10 m/pixel) up to 1 km across, spanning forms from crisp steep-walled pits, to subtle albedo rings, to topographic rings, with all ranges of morphologic gradation. Three gravitationally low regions of the comet have smoother terrain, parts of which appear to be deposits from minimally modified flows, with other parts likely to be heavily eroded portions of multiple layer piles. Changes observed between the two missions are primarily due to backwasting of scarps bounding one of these probable flow deposits. This style of erosion is also suggested by remnant mesa forms in other areas of smoother terrain. The two distinct terrains suggest either an evolutionary change in processes, topographically- controlled processes, or a continuing interaction of erosion and deposition.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN9320 , Icarus; 222; 2; 453-466
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  • 3
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    Episodes of Particle Ejection from the Surface of the Active Asteroid (101955) Bennu (2019)
    In:  CASI
    Details
    Publication Date: 2020-01-04
    Description: Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and SecurityRegolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN76455 , Science (ISSN 0036-8075) (e-ISSN 1095-9203); 366; 6470; eaay3544
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  • 4
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    Nature of the "Orange" Material on Vesta From Dawn (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: 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).
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-30106 , Vesta in the Light of Dawn: First Exploration of a Protoplanet in the Asteroid Belt; Feb 03, 2014 - Feb 04, 2014; Houston, TX; United States
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  • 5
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    Global View of the Bright Material on Vesta (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: At 525 km in mean diameter, Vesta is the second-most massive and one of the brightest asteroids of the main-belt. Here we give a global view of the bright material (BM) units on Vesta. We classified the BMs according to the normal visual albedo. The global albedo map of Vesta allows to be divided the surface into three principal types of terrains: bright regions, dark regions and intermediate regions. The distribution of bright regions is not uniform. The mid-southern latitudes contain the most bright areas, while the northern hemisphere is poor in bright regions. The analysis of the spectral parameters and the normal visual albedo show a dependence between albedo and the strength (depth) of ferrous iron absorption bands, strong bands correspond with high albedo units. Vesta's average albedo is 0.38, but there are bright material whose albedo can exceed 0.50. Only the E-Type asteroids have albedos comparable to those of the BMs on Vesta. The Dawn mission observed a large fraction of Vesta's surface at high spatial resolution, allowing a detailed study of the morphology and mineralogy of it. In particular, reflectance spectra provided by the Visible and InfraRed spectrometer (VIR), confirmed that Vesta's mineralogy is dominated by pyroxenes. All Vesta spectra show two strong absorption bands at approx 0.9 and 1.9 micron, typical of the pyroxenes and associated with the howardite, eucrite and diogenite (HED) meteorites.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN 30108 , Vesta in the Light of Dawn: First Exploration of a Protoplanet in the Asteroid Belt; Feb 03, 2014 - Feb 04, 2014; Houston, TX; United States
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  • 6
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    Small Next-Generation Atmospheric Probe (SNAP) Concept (2017)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We present the Small Next-Generation Atmospheric Probe (SNAP) as a secondary payload concept for future missions to giant planets. As a case study, we examine the advantages, cost and risk of adding SNAP to the future Uranus Orbiter and Probe flag-ship mission; in combination with the missions main probe, SNAP would perform atmospheric in-situ measurements at a second location.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC-E-DAA-TN43959 , International Planetary Probe Workshop (IPPW-14) 2017; Jul 12, 2017 - Jul 16, 2017; The Hague; Netherlands
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  • 7
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    Does Vesta Have Moons? (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: Previous searches for moons around Vesta have found nothing to an upper limit of 22.5 magnitude, that corresponds to 44 +/- 4 m diameter assuming the same albedo as Vesta. The Dawn mission's approach phase has dedicated satellite search observations consisting of two mosaic sequences bracketing the first observations of a complete rotation of Vesta scheduled for early July, 2011. In addition, we use the approach optical navigation image sequences for initial satellite searches. We will report any findings from these observations, and upper limits of magnitude and size.
    Keywords: Lunar and Planetary Science and Exploration
    Type: GSFC.ABS.4470.2011 , 74th Annual Meeting of the Meteoritical Society; Aug 08, 2011 - Aug 12, 2011; London; United Kingdom
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  • 8
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    Oscillatory Zoning and Aqueous Alteration of Fayalitic Olivine from the LEW 90500 CM2 Chondrite (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Lunar and Planetary Science and Exploration
    Type: Meteoritics and Planetary Science Suppl.|65th Ann. Mtg. Meteoritical Soc.; Jul 01, 2002; Los Angeles, CA; United States
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