Examinando por Autor "Fornasier, S."

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Acceso Abierto
Multidisciplinary analysis of the Hapi region located on Comet 67P/Churyumov–Gerasimenko
(Oxford Academics: Oxford University Press, 2019-05-07) Pajola, M.; Lee, J. C.; Oklay, N.; Hviid, S. F.; Penasa, L.; Mottola, S.; Shi, X.; Fornasier, S.; Davidsson, B. J. R.; Giacomini, L.; Lucchetti, A.; Massironi, M.; Vicent, J. B.; Bertini, I.; Naletto, G.; Ip, W. H.; Sierks, H.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Keller, H. U.; Agarwal, J.; Barucci, M. A.; Bertaux, J. L.; Bodewits, D.; Cambianica, P.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Deller, J.; El Maarry, M. R.; Feller, C.; Ferrari, S.; Fulle, M.; Gutiérrez, Pedro J.; Güttler, C.; Lara, L. M.; La Forgia, F.; Lazzarin, M.; Lin, Z. Y.; López Moreno, J. J.; Marzari, F.; Preusker, F.; Scholten, F.; Toth, I.; Tubiana, C.; European Space Agency (ESA); Pajola, M. [0000-0002-3144-1277]; Penasa, L. [0000-0002-6394-3108]; Fornasier, S. [0000-0001-7678-3310]; Lucchetti, A. [0000-0001-7413-3058]; Vicent, J. B. [0000-0001-6575-3079]; Naletto, G. [0000-0003-2007-3138]; Barucci, M. A. [0000-0002-1345-0890]; Bertaux, J. L. [0000-0003-0333-229X]; Deller, J. [0000-0001-8341-007X]; Fulle, M. [0000-0001-8435-5287]; Güttler, C. [0000-0003-4277-1738]; Tubiana, C. [0000-0001-8475-9898]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
By using the Rosetta/OSIRIS-NAC data set taken in 2014 August, we focus on the neck region, called Hapi, located on 67P Churyumov–Gerasimenko’s Northern hemisphere. The gravitational potential and slopes of Hapi, coupled with the geological unit identification and the boulder size–frequency distributions, support the interpretation that both taluses and gravitational accumulation deposits observable on Hapi are the result of multiple cliff collapses that occurred at different times. By contrast, the fine-particle deposits observable in the central part of the study area are made of aggregates coming from the Southern hemisphere and deposited during each perihelion passage. Both the consolidated terrains on the western part of Hapi, as well as the centrally aligned ridge made of boulder-like features, suggest that Hapi is in structural continuity with the onion-like structure of the main lobe of 67P. Despite the dusty blanket observable on Hapi, its terrains are characterized by water-ice-rich components that, once repeatedly and rapidly illuminated, sublimate, hence resulting in the strong jet activity observed in 2014 August.
Acceso Abierto
Quantitative analysis of isolated boulder fields on comet 67P/Churyumov-Gerasimenko
(EDP Sciences, 2019-09-20) Cambianica, P.; Cremonese, G.; Naletto, G.; Lucchetti, A.; Pajola, M.; Penasa, L.; Simioni, E.; Massironi, M.; Ferrari, S.; Bodewits, D.; La Forgia, F.; Sierks, H.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Davidsson, B. J. R.; Barucci, M. A.; Bertaux, J. L.; Bertini, I.; Da Deppo, V.; Debei, S.; De Cecco, M.; Deller, J.; Fornasier, S.; Fulle, M.; Gutiérrez, Pedro J.; Güttler, C.; Ip, W. H.; Keller, H. U.; Lara, L. M.; Lazzarin, M.; Lin, Z. Y.; López Moreno, J. J.; Marzari, F.; Mottola, S.; Shi, X.; Scholten, F.; Toth, I.; Tubiana, C.; Vicent, J. B.; https://orcid.org/0000-0002-8091-4915; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Aims. We provide a detailed quantitative analysis of isolated boulder fields situated in three different regions of comet 67P/Churyumov-Gerasimenko: Imhotep, Hapi, and Hatmehit. This is done to supply a useful method for analyzing the morphology of the boulders and to characterize the regions themselves. Methods. We used OSIRIS Narrow Angle Camera images with a spatial scale smaller than 2 m px−1 and analyzed the size-frequency distribution and the cumulative fractional area per boulder population. In addition, we correlated shape parameters, such as circularity and solidity, with both the spatial and the size-frequency distribution of the three populations. Results. We identified 11 811 boulders in the Imhotep, Hapi, and Hatmehit regions. We found that the Hatmehit and Imhotep areas show power indices in the range of −2.3/−2.7. These values could represent a transition between gravitational events caused by thermal weathering and sublimation, and material formed during collapses that has undergone sublimation. The Hapi area is characterized by a lower power index (−1.2/−1.7), suggesting that those boulders have a different origin. They can be the result of material formed during gravitational events and collapses that has undergone continuous fragmentation. We calculated the cumulative fractional area (CFA) in order to investigate how the area is covered by boulders as a function of their sizes. The Hatmehit and Imhotep regions show a CFA that is well fit by a power law. In contrast, the Hapi area does not show the same trend. We analyzed the fractal distributions, finding that the populations seem to be fractal at all dimensions, except for the Hapi distribution, which shows a possible fractal behavior for small dimensions only. Finally, the average values of the shape parameters reveal solid and roundish boulders in all populations we studied.
Acceso Abierto
Rosetta/OSIRIS observations of the 67P nucleus during the April 2016 flyby: high-resolution spectrophotometry
(EDP Sciences, 2019-09-20) Feller, C.; Fornasier, S.; Ferrari, S.; Hasselmann, P. H.; Barucci, M. A.; Massironi, M.; Deshapriya, J. D. P.; Sierks, H.; Naletto, G.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Davidsson, Björn J. R.; Bertaux, J. L.; Bertini, I.; Bodewits, D.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Fulle, M.; Gutiérrez, Pedro J.; Güttler, C.; Ip, W. H.; Keller, H. U.; Lara, L. M.; Lazzarin, M.; López Moreno, J. J.; Marzari, F.; Shi, X.; Tubiana, C.; Gaskell, B.; La Forgia, F.; Lucchetti, A.; Mottola, S.; Pajola, M.; Preusker, F.; Scholten, F.; 0000-0002-2941-3875; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Context. From August 2014 to September 2016, the Rosetta spacecraft followed comet 67P/Churyumov–Gerasimenko along its orbit. After the comet passed perihelion, Rosetta performed a flyby manoeuvre over the Imhotep–Khepry transition in April 2016. The OSIRIS/Narrow-Angle-Camera (NAC) acquired 112 observations with mainly three broadband filters (centered at 480, 649, and 743 nm) at a resolution of up to 0.53 m/px and for phase angles between 0.095° and 62°. Aims. We have investigated the morphological and spectrophotometrical properties of this area using the OSIRIS/NAC high-resolution observations. Methods. We assembled the observations into coregistered color cubes. Using a 3D shape model, we produced the illumination conditions and georeference for each observation. We mapped the observations of the transition to investigate its geomorphology. Observations were photometrically corrected using the Lommel–Seeliger disk law. Spectrophotometric analyses were performed on the coregistered color cubes. These data were used to estimate the local phase reddening. Results. The Imhotep–Khepry transition hosts numerous and varied types of terrains and features. We observe an association between a feature’s nature, its reflectance, and its spectral slopes. Fine material deposits exhibit an average reflectance and spectral slope, while terrains with diamictons, consolidated material, degraded outcrops, or features such as somber boulders present a lower-than-average reflectance and higher-than-average spectral slope. Bright surfaces present here a spectral behavior consistent with terrains enriched in water-ice. We find a phase-reddening slope of 0.064 ± 0.001%/100 nm/° at 2.7 au outbound, similar to the one obtained at 2.3 au inbound during the February 2015 flyby. Conclusions. Identified as the source region of multiple jets and a host of water-ice material, the Imhotep–Khepry transition appeared in April 2016, close to the frost line, to further harbor several potential locations with exposed water-ice material among its numerous different morphological terrain units.
Acceso Abierto
Seasonal variations in source regions of the dust jets on comet 67P/Churyumov-Gerasimenko
(EDP Sciences, 2019-09-20) Lai, I. L.; Ip, W. H.; Lee, J. C.; Lin, Z. Y.; Vicent, J. B.; Oklay, N.; Sierks, H.; Barbieri, C.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Rickman, H.; Keller, H. U.; Agarwal, J.; Barucci, M. A.; Bertaux, J. L.; Bertini, I.; Bodewits, D.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B. J. R.; Debei, S.; De Cecco, M.; Deller, J.; Fornasier, S.; Fulle, M.; Groussin, O.; Gutiérrez, Pedro J.; Güttler, C.; Hofmann, M.; Hviid, S. F.; Jorda, L.; Knollenberg, J.; Kovács, G.; kramm, J. R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; López Moreno, J. J.; Marzari, F.; Naletto, G.; Shi, X.; Tubiana, C.; Thomas, N.; Ministry of Science and Technology, Taiwan (MOST)
Aims. We investigate the surface distribution of the source regions of dust jets on comet 67P/Churyumov-Gerasimenko as a function of time. Methods. The dust jet source regions were traced by the comprehensive imaging data set provided by the OSIRIS scientific camera. Results. We show in detail how the projected footpoints of the dust jets and hence the outgassing zone would move in consonance with the sunlit belt. Furthermore, a number of source regions characterized by repeated jet activity might be the result of local topographical variations or compositional heterogeneities. Conclusions. The spatial and temporal variations in source regions of the dust jets are influenced significantly by the seasonal effect. The strong dependence on the solar zenith angle and local time could be related to the gas sublimation process driven by solar insolation on a surface layer of low thermal inertia.
Acceso Abierto
The backscattering ratio of comet 67P/Churyumov–Gerasimenko dust coma as seen by OSIRIS onboard Rosetta
(Oxford Academics: Oxford University Press, 2019-01-22) Bertini, I.; La Forgia, F.; Fulle, M.; Tubiana, C.; Güttler, C.; Moreno, F.; Agarwal, J.; Muñoz, O.; Mottola, S.; Ivanovsky, S.; Pajola, M.; Lucchetti, A.; Petropoulou, V.; Lazzarin, M.; Rotundi, A.; Bodewits, D.; Frattin, E.; Toth, I.; Masoumzadeh, N.; Kovács, G.; Rinaldi, G.; Guirado, D.; Sierks, H.; Naletto, G.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Davidsson, B. J. R.; Barbieri, C.; Barucci, M. A.; Bertaux, J. L.; Cambianica, P.; Cremonese, G.; Da Deppo, V.; Debei, S.; De Cecco, M.; Deller, J.; Ferrari, S.; Ferri, F.; Fornasier, S.; Gutiérrez, Pedro J.; Hasselmann, P. H.; Ip, W. H.; Keller, H. U.; Lara, L. M.; López Moreno, J. J.; Marzari, F.; Massironi, M.; Penasa, L.; Shi, X.; Fulle, M. [0000-0001-8435-5287]; Tubiana, C. [0000-0001-8475-9898]; Güttler, C. [0000-0003-4277-1738]; Pajola, M. [0000-0002-3144-1277]; Rinaldi, G. [0000-0002-2968-0455]; Naletto, G. [0000-0003-2007-3138]; Barucci, M. A. [0000-0002-1345-0890]; Bertaux, J. L. [0000-0003-0333-229X]; Deller, J. [0000-0001-8341-007X]; Fornasier, S. [0000-0001-7678-3310]; Penasa, L. [0000-0002-6394-3108]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Remote sensing observations of dust particles ejected from comets provide important hints on the intimate nature of the materials composing these primitive objects. The measurement of dust coma backscattering ratio, BSR, defined as the ratio of the reflectance at phase angle 0° and 30°, helps tuning theoretical models aimed at solving the inverse scattering problem deriving information on the nature of the ejected particles. The Rosetta/OSIRIS camera sampled the coma phase function of comet 67P, with four series acquired at low phase angles from 2015 January to 2016 May. We also added previously published data to our analysis to increase the temporal resolution of our findings. We measured a BSR in the range ∼ [1.7–3.6], broader than the range found in literature from ground-based observations of other comets. We found that during the post-perihelion phase, the BSR is systematically larger than the classical cometary dust values only for nucleocentric distances smaller than ∼100 km. We explain this trend in terms of a cloud of chunks orbiting the nucleus at distances <100 km ejected during perihelion and slowly collapsing on the nucleus over a few months because of the coma gas drag. This also implies that the threshold particle size for the dust phase function to become similar to the nucleus phase function is between 2.5 mm and 0.1 m, taking into account previous Rosetta findings.
Acceso Abierto
The Rocky‐Like Behavior of Cometary Landslides on 67P/Churyumov‐Gerasimenko
(American Geophysical Union: Advancing Earth and Space Science, 2019-12-18) Lucchetti, A.; Penasa, L.; Pajola, M.; Massironi, M.; Teresa Brunetti, M.; Cremonese, G.; Oklay, N.; Vicent, J. B.; Mottola, S.; Fornasier, S.; Sierks, H.; Naletto, G.; Lamy, Philippe; Rodrigo, Rafael; Koschny, D.; Davidsson, B. J. R.; Barbieri, C.; Antonietta Barucci, M.; Bertaux, J. L.; Bertini, I.; Bodewits, D.; Cambianica, P.; Da Deppo, V.; Debei, S.; De Cecco, M.; Deller, J.; Ferrari, S.; Ferri, F.; Franceschi, M.; Fulle, M.; Gutiérrez, Pedro J.; Güttler, C.; Ip, W. H.; Keller, H. U.; Lara, L.; Lazzarin, M.; López Moreno, J. J.; Marzari, F.; Tubiana, C.; Lucchetti, A. [0000-0001-7413-3058]; Ferrari, S. [0000-0002-0157-3463]; Lara, L. [0000-0002-7184-920X]; Franceschi, M. [0000-0002-2061-0151]; Debei, S. [0000-0002-6757-6616]; Fulle, M. [0000-0001-8435-5287]; López Moreno, J. J. [0000-0002-7946-2624]; Penasa, L. [0000-0002-6394-3108]; Pajola, M. [0000-0002-3144-1277]; Ferri, F. [0000-0003-2395-5275]; Bertini, I. [0000-0002-0616-2444]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
Landslides have been identified on several solar system bodies, and different mechanisms have been proposed to explain their runout length. We analyze images from the Rosetta mission and report the global characterization of such features on comet 67P/Churyumov‐Gerasimenko's surface. By assuming the height to runout length as an approximation for the friction coefficient of landslide material, we find that on comet 67P, this ratio falls between 0.50 and 0.97. Such unexpected high values reveal a rocky‐type mechanical behavior that is much more akin to Earth dry landslides than to icy satellites' mass movements. This behavior indicates that 67P and likely comets in general are characterized by consolidated materials possibly rejecting the idea that they are fluffy aggregates. The variability of the runout length among 67P landslides can be attributed to the different volatile content located in the top few meters of the cometary crust, which can drive the mass movement.