Showing papers by "M. C. De Sanctis published in 2017"

Localized aliphatic organic material on the surface of Ceres

Abstract: Organic compounds occur in some chondritic meteorites, and their signatures on solar system bodies have been sought for decades. Spectral signatures of organics have not been unambiguously identified on the surfaces of asteroids, whereas they have been detected on cometary nuclei. Data returned by the Visible and InfraRed Mapping Spectrometer on board the Dawn spacecraft show a clear detection of an organic absorption feature at 3.4 micrometers on dwarf planet Ceres. This signature is characteristic of aliphatic organic matter and is mainly localized on a broad region of ~1000 square kilometers close to the ~50-kilometer Ernutet crater. The combined presence on Ceres of ammonia-bearing hydrated minerals, water ice, carbonates, salts, and organic material indicates a very complex chemical environment, suggesting favorable environments to prebiotic chemistry.

Spectral analysis of Ahuna Mons from Dawn mission's visible-infrared spectrometer

Abstract: Ahuna Mons is the highest mountain on Ceres. A unique complex in terms of size, shape, and morphology, Ahuna is bordered by flanks of the talus around its summit. Recent work by Ruesch et al. [2016] based on Dawn's Framing Camera images shed light on the possible origin of Ahuna Mons. According to Ruesch et al. [2016], Ahuna Mons is formed by a volcanic process involving the ascent of cryomagma and extrusion onto the surface followed by dome development and subsequent spreading. Here we analyzed in detail the composition of Ahuna Mons, using data acquired by the Visible and InfraRed spectrometer aboard Dawn. The spectral analysis reveals a relatively high abundance of carbonates and a non-homogeneous variation in carbonates composition and abundance along Ahuna's flanks, associated with a lower amount of the Ceres's ubiquitous NH4-phyllosilicates over a large portion of the flanks. The grain size is coarser on the flanks than in the surrounding regions, suggesting the presence of fresher material, also compatible with a larger abundance of carbonates. Thermal variations are seen in Ahuna, supporting the evidence of different compactness of the surface regolith in specific locations. Results of the spectral analysis are consistent with a possible cryovolcanic origin which exposed fresher material that slid down on the flanks.

Pitted terrains on (1) Ceres and implications for shallow subsurface volatile distribution

Abstract: Prior to the arrival of the Dawn spacecraft at Ceres, the dwarf planet was anticipated to be ice-rich. Searches for morphological features related to ice have been ongoing during Dawn's mission at Ceres. Here we report the identification of pitted terrains associated with fresh Cerean impact craters. The Cerean pitted terrains exhibit strong morphological similarities to pitted materials previously identified on Mars (where ice is implicated in pit development) and Vesta (where the presence of ice is debated). We employ numerical models to investigate the formation of pitted materials on Ceres and discuss the relative importance of water ice and other volatiles in pit development there. We conclude that water ice likely plays an important role in pit development on Ceres. Similar pitted terrains may be common in the asteroid belt and may be of interest to future missions motivated by both astrobiology and in situ resource utilization.

Spectrophotometric properties of dwarf planet Ceres from VIR onboard Dawn mission

Abstract: Aims. We present a study of the spectrophotometric properties of dwarf planet Ceres in the visual-to-infrared (VIS-IR) spectral range by means of hyper-spectral images acquired by the VIR imaging spectrometer on board the NASA Dawn mission. Methods. Disk-resolved observations with a phase angle within the 7 ◦ < α < 132 ◦ interval were used to characterize Ceres’ phase curve in the 0.465-4.05 µm spectral range. Hapke’s model was applied to perform the photometric correction of the dataset to standard observation geometry at VIS-IR wavelength, allowing us to produce albedo and color maps of the surface. The V-band magnitude phase function of Ceres as been computed from disk-resolved images and fitted with both the classical linear model and H-G formalism. Results. The single- scattering albedo and the asymmetry parameter at 0.55 µm are w = 0.14±0.02 and ξ = −0.11±0.08, respectively (two-lobe Henyey-Greenstein phase function); at the same wavelength, Ceres’ geometric albedo as derived from our modeling is 0.094±0.007; the roughness parameter is ¯ θ = 29 ◦ ±6 ◦ . Albedo maps indicate small variability on a global scale with an average reflectance at standard geometry of 0.034 ± 0.003. Nonetheless, isolated areas such as the Occator bright spots, Haulani, and Oxo show an albedo much higher than average. We measure a significant spectral phase reddening, and the average spectral slope of Ceres’ surface after photometric correction is 1.1%kA −1 and 0.85%kA −1 at VIS and IR wavelengths, respectively. Broadband color indices are V−R = 0.38±0.01 and R−I = 0.33±0.02. Color maps show that the brightest features typically exhibit smaller slopes. The H-G modeling of the V-band magnitude phase curve for α < 30 ◦ gives H = 3.14±0.04 and G = 0.10±0.04, while the classical linear model provides V(1,1,0 ◦ ) = 3.48±0.03 and β = 0.036±0.002. The comparison of our results with spectrophotometric properties of other minor bodies indicates that Ceres has a less back-scattering phase function and a slightly higher albedo than comets and C-type objects. However, the latter represents the closest match in the usual asteroid taxonomy.

Spectrophotometric properties of dwarf planet Ceres from the VIR spectrometer on board the Dawn mission

Abstract: Aims. We present a study of the spectrophotometric properties of dwarf planet Ceres in the visual-to-infrared (VIS-IR) spectral range by means of hyper-spectral images acquired by the VIR imaging spectrometer on board the NASA Dawn mission.Methods. Disk-resolved observations with a phase angle within the 7° m spectral range. Hapke’s model was applied to perform the photometric correction of the dataset to standard observation geometry at VIS-IR wavelength, allowing us to produce albedo and color maps of the surface. The V -band magnitude phase function of Ceres has been computed from disk-resolved images and fitted with both the classical linear model and H-G formalism.Results. The single-scattering albedo and the asymmetry parameter at 0.55 μ m are w = 0.14 ± 0.02 and ξ = −0.11 ± 0.08, respectively (two-lobe Henyey-Greenstein phase function); at the same wavelength, Ceres’ geometric albedo as derived from our modeling is 0.094 ± 0.007; the roughness parameter is . Albedo maps indicate small variability on a global scale with an average reflectance at standard geometry of 0.034 ± 0.003. Nonetheless, isolated areas such as the Occator bright spots, Haulani, and Oxo show an albedo much higher than average. We measure a significant spectral phase reddening, and the average spectral slope of Ceres’ surface after photometric correction is 1.1% kA-1 and 0.85% kA-1 at VIS and IR wavelengths, respectively. Broadband color indices are V −R = 0.38 ± 0.01 and R −I = 0.33 ± 0.02. Color maps show that the brightest features typically exhibit smaller slopes. The H-G modeling of the V -band magnitude phase curve for α = 3.14 ± 0.04 and G = 0.10 ± 0.04, while the classical linear model provides V (1,1,0°) = 3.48 ± 0.03 and β = 0.036 ± 0.002. The comparison of our results with spectrophotometric properties of other minor bodies indicates that Ceres has a less back-scattering phase function and a slightly higher albedo than comets and C-type objects. However, the latter represents the closest match in the usual asteroid taxonomy.

An investigation of the bluish material on Ceres

Abstract: The dwarf planet Ceres shows spatially well-defined regions, which exhibit a negative (blue) spectral slope between 0.5 and 2.5 µm. Comparisons with planetary bodies known to exhibit a blue slope and spectral properties of materials identified on Ceres’ surface based on infrared wavelength signatures indicate the spectral changes could be related to physical properties of the surface material rather than variations in its composition. The close association of bluish surface regions to fresh impact craters implies a possible relationship to an impact-triggered alteration and/or space weathering processes. The bluish regions could be linked with blankets of ultra-fine grains and partly amorphous phyllosilicates, which form larger agglomerates due to the sticky behavior of impact induced phyllosilicate dust and/or the amorphization of the ejecta material during the impact process. Space weathering processes (micro-meteoritic impacts, temperature changes) cause a reversal of the agglutination process and a re-crystallization of the surface material with time resulting in a reddening of the spectral slope.

Exposed H2O-Rich Areas on Ceres Detected by Dawn

Abstract: 1 , A. Raponi 2 , F. Tosi 2 , M.C. De Sanctis 2 , E. Ammannito 2,3 , F.G. Carrozzo 2 , M. E. Landis 4 , S. Byrne 4 , U. Carsety 5 , S. Schröder 5 , T. Platz 6 , O. Ruesch 7 , K. Hughson 3 , T. B. McCord 1 , S. Singh 1 , K. Johnson 1 , F. Zambon 2 , C.M. Pieters 8 , C.A. Raymond 9 , C.T. Russell 3 , and the Dawn/VIR Team, 1 1 Bear Fight Institute, Winthrop, WA, USA. 2 INAF-IAPS Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy. 3 University of California at Los Angeles, Los Angeles, CA, USA. 4 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. 5 German Aerospace Center (DLR), Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany. 6 Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany. 7 NASA/Goddard Space Flight Center, Greenbelt, MD, USA. 8 Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA. 9 NASA/Jet Propulsion Laboratory and California Institute of Technology, Pasadena, CA, USA.

Mineralogical mapping of the Occator Quadrangle

Abstract: LONGOBARDO, Andrea1, PALOMBA, Ernesto2, DE SANCTIS, Maria Cristina2, BUCZKOWSKI, Debra3, CARROZZO, Filippo Giacomo1, GALIANO, Anna1, TOSI, Federico2, ZAMBON, Francesca2, RAPONI, Andrea2, CIARNIELLO, Mauro2, AMMANNITO, Eleonora4, STEPHAN, Katrin5, MCFADDEN, Lucy A.6, FRIGERI, Alessandro2, CAPRIA, Maria Teresa2, FONTE, Sergio2, GIARDINO, Marco2, RAYMOND, Carol A.7 and RUSSELL, Christopher T.8, (1)IAPS Istituto di Astrofisica e Planetologia Spaziali, INAF Istituto Nazionale di Astrofisica, Via del Fosso del Cavaliere, 100, Rome, I-00133, Italy, (2)INAF Istituto Nazionale di Astrofisica, IAPS Istituto di Astrofisica e Planetologia Spaziali, Via del Fosso del Cavaliere, 100, Rome, I-00133, Italy, (3)John Hopkins University, Laurel, MD 21218, (4)IGPP, UCLA, Los Angeles, CA 90094, (5)German Aerospace Center, Institute of Planetary Research, Rutherfordstrasse 2, Berlin, 12489, Germany, (6)NASA, GSFC, Greenbelt, MD 20771, (7)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, (8)Earth and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567, andrea.longobardo@iaps.inaf.it

Bright Spots on Ceres: Occator, Oxo, and the Others

Abstract: The dwarf planet Ceres has a very dark surface (average reflectance at 0.55 m is 0.03 [1]) with some bright areas detected during the early phases of Dawn mission [2] and identified as “bright spots” (BS). The brightest among these are located on the floor of Occator crater, named Cerealia Facula and Vinalia Faculae. By using the hyperspectral data provided by the VIR instrument [3], a catalogue of 98 BS was obtained [4]. A spectral analysis of these BS has been performed in order to reveal if they have a common or a different origin and evolution. BS general distribution and characteristics: BS have no preferential orientation or location, even if many of them are located on younger terrains. The highest concentration of BS is found on the Rongo [5] and the Yalode quadrangles [6] with 14 and 15 BS, respectively. The majority of BS are features related to impacts, while the remaining ones are areal and linear features. BS spectra are diverse. First of all, the reflectance continuum varies by a factor of three between Occator spots (reflectance at 30° phase is 0.11) and the “darkest” BS’s (0.034). Spectra of Dantu, Oxo and Occator are shown in Figure 1, representing three different cases of BS. The Dantu (17°N 135°E) BS spectrum reveals weak, but clear, carbonate bands (3.4 and 4 m [7]), and strong ammoniated and OH features (3.05 and 2.7 m, respectively [8]). The Oxo (43°N 0°E) BS spectrum exhibits very strong carbonate bands and both the 3.05 m and the 2.7 m features. However, the latter have a different shape from the Dantu case. In both Occator BS (20°N; 239°E 241°E, respectively) spectra, the ammoniated feature disappears, the OH band remains strong but becomes sharper, and the carbonate band depths increase. For the first time and uniquely here there is the appearance of a weaker 2.2 m band, due to possible ammoniated salts [8]. Bright Spots Compositional properties: Carbonate composition. The 3.4 and 4 m carbonate overtone band depths (BD) are an indirect measurement of carbonate abundance and in this respect the Cerealia and Vinalia Faculae, Oxo and Ezinu (61°N 221°E) are the BS’s with the largest carbonate abundances (Fig.2a). Band depths of carbonate features are defined as 1-Rc/Rb, where Rb is the reflectance of band minimum after removed continuum and Rc is the reflectance of the continuum at the same wavelength of band minimum [9]. Band depth values of Cerealia and Vinalia Faculae, Oxo and Ezinu are located in the upper part of the 4 vs 3.4 m band depth scatterplot which show an expected strong linear correlation with very few exceptions, strongly indicating that both bands are due to the same phase. As an example, the Ernutet BS shows a 3.4 m BD overtone excess with respect to the 4 m and this could be due to the presence in this area (even if not exactly overlapped to the bright spot) of aliphatic organics (which absorb strongly in the 3.4 m region), as recently detected by [10]. Conversely, an excess of 4.0 m BD is observed in some other cases, but differently from the Ernutet case. This does not imply a compositional difference and could be simply explained by the different carbonate grain size in these BS’s, where one of the two absorption bands is optically saturated. The composition of carbonates in BS’s is generally similar to the average Ceres, with Mg-Ca carbonates mixed with dark components, hydrated and ammoniated compounds. However, there are particular cases in which the prevalent carbonate is Na-bearing as shown in Fig.2b. Ammonia and OH bearing materials. Ammoniated clays are ubiquitous on Ceres and common in BS’s, too. However, their abundance decreases with increasing brightness and increasing carbonate BD, and their absorption bands completely disappear on Cerealia and Vinalia Flaculae. A similar anticorrelation trend, although less strong, exists between carbonates and phyllosilicates. In particular, the Oxo and Ezinu’s BSs are among the most OH-depleted and richest in carbonates. A peculiar trend is observed for the two spots in Occator, which exhibit a moderately strong phyllosilicate 2.7 m band, comparable with carbonate poorer BS’s. A possible explanation of this behavior can be found in the different nature of hydrated materials in Occator, where Al-pyllosilicates are present instead of the Mg-phyllosilicates that are common in the rest of the BS’s. 1566.pdf Lunar and Planetary Science XLVIII (2017)

Spectral Investigation of Quadrangle Ac-H-3 of the Dwarf Planet Ceres - The Region of Impact Crater Dantu

Abstract: Abstract Mapping Ceres’ surface composition in the Dantu region, located between 21°–66°N and 90°–180°E, offers the unique possibility to investigate changes in the surface composition related to different stratigraphic levels of Ceres’ crust. Dantu is located in a huge depression named Vendimia Planitia, which possibly represents a completely degraded impact basin formed in the beginning of Ceres’ geological history. Most parts of this depression are characterized by strong phyllosilicate absorptions, which are stronger than elsewhere on Ceres’ surface. This spectral signature possibly is related to the material emplaced at the time of the Vendimia impact event excavating material from deeper regions of Ceres’ crust. Subsequent impacts in this basin reach far deeper into Ceres’ crust than any impact events outside of Vendemia Planitia, which could explain the spectral signature of Dantu, possibly pointing to a higher concentration of ammonium-bearing phyllosilicates in Ceres’ deeper crust. Spectral differences with respect to the small fresh craters on Dantu's floor are probably related to grain size effects causing a bluish visible slope as observed by fresh impact craters on other places on Ceres. The local enrichment of carbonates in the Dantu area could also be associated with the impact event and may have been formed by additional impact-triggered and/or post-impact alteration processes.

Large-Scale Heterogeneity of Ceres: Clues to Interior Evolution

Abstract: J. C. Castillo-Rogez, A. Ermakov, R. S. Park, S. Marchi, M. T. Bland, R. R. Fu, G. Mitri, E. Ammannito, M. C. De Sanctis, M. J. Toplis, T. H. Prettyman, C. T. Russell; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA (carol.a.raymond@jpl.nasa.gov); 2 Southwest Research Institute, Boulder, CO, USA; USGS Astrogeology Center, Flagstaff, AZ, USA; Lamont-Doherty Earth Observatory, Earth Institute, Columbia University, Palisades, NY 10964, USA; Univ. of Nantes, Nantes, France; University of California Los Angeles, IGPP/EPSS, Los Angeles, CA, 90095, USA; IAPS, Rome, Italy; IRAP, University of Toulouse, Toulouse, France; Planetary Science Institute, Tucson, AZ, USA.