@article{RinaldiFormisanoKappeletal.2019, author = {Rinaldi, G. and Formisano, M. and Kappel, David and Capaccioni, F. and Bockelee-Morvan, D. and Cheng, Y-C and Vincent, J-B and Deshapriya, P. and Arnold, G. and Capria, M. T. and Ciarniello, M. and De Sanctis, M. C. and Doose, L. and Erard, S. and Federico, C. and Filacchione, G. and Fink, U. and Leyrat, C. and Longobardo, A. and Magni, G. and Mighorini, A. and Mottola, S. and Naletto, G. and Raponi, A. and Taylor, F. and Tosi, F. and Tozzi, G. P. and Salatti, M.}, title = {Analysis of night-side dust activity on comet 67P observed by VIRTIS-M}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {630}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201834907}, pages = {16}, year = {2019}, abstract = {On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25-36 W K-1 m(-2) s(-1/2). These thermal inertia values can be used to verify with a 3D finite-element method (REM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m(-2) K-1 S-0.5 ; (2) the same structure, but with thermal inertia of 100 J m(-2) K-1 S-0.5; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 +/- 4.8\%/100 nm to 13 +/- 2.6\%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between -2.5 and -3.}, language = {en} } @article{RousseauErardBecketal.2018, author = {Rousseau, Batiste and Erard, St{\´e}phane and Beck, P. and Quirico, Eric and Schmitt, B. and Brissaud, O. and Montes-Hernandez, G. and Capaccioni, F. and Filacchione, Gianrico and Bockelee-Morvan, Dominique and Leyrat, C. and Ciarniello, M. and Raponi, Andrea and Kappel, David and Arnold, G. and Moroz, L. V. and Palomba, Ernesto and Tosi, Federico}, title = {Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-mu m sized cosmochemical analogues}, series = {Icarus : international journal of solar system studies}, volume = {306}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, organization = {VIRTIS Team}, issn = {0019-1035}, doi = {10.1016/j.icarus.2017.10.015}, pages = {306 -- 318}, year = {2018}, abstract = {Laboratory spectral measurements of relevant analogue materials were performed in the framework of the Rosetta mission in order to explain the surface spectral properties of comet 67P. Fine powders of coal, iron sulphides, silicates and their mixtures were prepared and their spectra measured in the Vis-IR range. These spectra are compared to a reference spectrum of 67P nucleus obtained with the VIRTIS/Rosetta instrument up to 2.7 mu m, excluding the organics band centred at 3.2 mu m. The species used are known to be chemical analogues for cometary materials which could be present at the surface of 67P. Grain sizes of the powders range from tens of nanometres to hundreds of micrometres. Some of the mixtures studied here actually reach the very low reflectance level observed by VIRTIS on 67P. The best match is provided by a mixture of sub-micron coal, pyrrhotite, and silicates. Grain sizes are in agreement with the sizes of the dust particles detected by the GIADA, MIDAS and COSIMA instruments on board Rosetta. The coal used in the experiment is responsible for the spectral slope in the visible and infrared ranges. Pyrrhotite, which is strongly absorbing, is responsible for the low albedo observed in the NIR. The darkest components dominate the spectra, especially within intimate mixtures. Depending on sample preparation, pyrrhotite can coat the coal and silicate aggregates. Such coating effects can affect the spectra as much as particle size. In contrast, silicates seem to play a minor role. (c) 2017 Elsevier Inc. All rights reserved.}, language = {en} } @article{TosiCapaccioniCapriaetal.2019, author = {Tosi, Federico and Capaccioni, F. and Capria, M. T. and Mottola, Stefano and Zinzi, A. and Ciarniello, M. and Filacchione, G. and Hofstadter, M. and Fonti, S. and Formisano, M. and Kappel, David and K{\"u}hrt, E. and Leyrat, C. and Vincent, J-B and Arnold, G. and De Sanctis, M. C. and Longobardo, Andrea and Palomba, E. and Raponi, A. and Rousseau, Batiste and Schmitt, Bernard and Barucci, Maria Antonietta and Bellucci, Giancarlo and Benkhoff, Johannes and Bockelee-Morvan, D. and Cerroni, P. and Combe, J-Ph and Despan, D. and Erard, St{\´e}phane and Mancarella, F. and McCord, T. B. and Migliorini, Alessandra and Orofino, V and Piccioni, G.}, title = {The changing temperature of the nucleus of comet 67P induced by morphological and seasonal effects}, series = {Nature astronomy}, volume = {3}, journal = {Nature astronomy}, number = {7}, publisher = {Nature Publ. Group}, address = {London}, issn = {2397-3366}, doi = {10.1038/s41550-019-0740-0}, pages = {649 -- 658}, year = {2019}, abstract = {Knowledge of the surface temperature distribution on a comet's nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov-Gerasimenko retrieved on the basis of infrared data acquired by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the Sun. We find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. The bilobate nucleus of comet 67P also induces daytime shadowing effects, which result in large thermal gradients. Over longer periods, VIRTIS-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface}, language = {en} } @article{CiarnielloFulleRaponietal.2022, author = {Ciarniello, Mauro and Fulle, Marco and Raponi, Andrea and Filacchione, Gianrico and Capaccioni, Fabrizio and Rotundi, Alessandra and Rinaldi, Giovanna and Formisano, Michelangelo and Magni, Gianfranco and Tosi, Federico and De Sanctis, Maria Cristina and Capria, Maria Teresa and Longobardo, Andrea and Beck, Pierre and Fornasier, Sonia and Kappel, David and Mennella, Vito and Mottola, Stefano and Rousseau, Batiste and Arnold, Gabriele}, title = {Macro and micro structures of pebble-made cometary nuclei reconciled by seasonal evolution}, series = {Nature astronomy}, volume = {6}, journal = {Nature astronomy}, number = {5}, publisher = {Nature Research}, address = {Berlin}, issn = {2397-3366}, doi = {10.1038/s41550-022-01625-y}, pages = {546 -- 553}, year = {2022}, abstract = {Comets evolve due to sublimation of ices embedded inside porous dust, triggering dust emission (that is, erosion) followed by mass loss, mass redistribution and surface modifications. Surface changes were revealed by the Deep Impact and Stardust NExT missions for comet 9P/Tempel 1 (ref.(1)), and a full inventory of the processes modifying cometary nuclei was provided by Rosetta while it escorted comet 67P/Churyumov-Gerasimenko for approximately two years(2-4). Such observations also showed puzzling water-ice-rich spots that stood out as patches optically brighter and spectrally bluer than the average cometary surfaces(5-9). These are up to tens of metres large and indicate macroscopic compositional dishomogeneities apparently in contrast with the structural homogeneity above centimetre scales of pebble-made nuclei(10). Here we show that the occurrence of blue patches determines the seasonal variability of the nucleus colour(4,11,12) and gives insight into the internal structure of comets. We define a new model that links the centimetre-sized pebbles composing the nucleus(10) and driving cometary activity(13,14) to metre-sized water-ice-enriched blocks embedded in a drier matrix. The emergence of blue patches is due to the matrix erosion driven by CO2-ice sublimation that exposes the water-ice-enriched blocks, which in turn are eroded by water-ice sublimation when exposed to sunlight. Our model explains the observed seasonal evolution of the nucleus and reconciles the available data at micro (sub-centimetre) and macro (metre) scales.}, language = {en} }