TY  - JOUR
A1  - Tosi, Federico
A1  - Capaccioni, F.
A1  - Capria, M. T.
A1  - Mottola, Stefano
A1  - Zinzi, A.
A1  - Ciarniello, M.
A1  - Filacchione, G.
A1  - Hofstadter, M.
A1  - Fonti, S.
A1  - Formisano, M.
A1  - Kappel, David
A1  - Kührt, E.
A1  - Leyrat, C.
A1  - Vincent, J-B
A1  - Arnold, G.
A1  - De Sanctis, M. C.
A1  - Longobardo, Andrea
A1  - Palomba, E.
A1  - Raponi, A.
A1  - Rousseau, Batiste
A1  - Schmitt, Bernard
A1  - Barucci, Maria Antonietta
A1  - Bellucci, Giancarlo
A1  - Benkhoff, Johannes
A1  - Bockelee-Morvan, D.
A1  - Cerroni, P.
A1  - Combe, J-Ph
A1  - Despan, D.
A1  - Erard, Stéphane
A1  - Mancarella, F.
A1  - McCord, T. B.
A1  - Migliorini, Alessandra
A1  - Orofino, V
A1  - Piccioni, G.
T1  - The changing temperature of the nucleus of comet 67P induced by morphological and seasonal effects
JF  - Nature astronomy
N2  - 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
Y1  - 2019
U6  - https://doi.org/10.1038/s41550-019-0740-0
SN  - 2397-3366
VL  - 3
IS  - 7
SP  - 649
EP  - 658
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Filacchione, Gianrico
A1  - Groussin, Olivier
A1  - Herny, Clemence
A1  - Kappel, David
A1  - Mottola, Stefano
A1  - Oklay, Nilda
A1  - Pommerol, Antoine
A1  - Wright, Ian
A1  - Yoldi, Zurine
A1  - Ciarniello, Mauro
A1  - Moroz, Lyuba
A1  - Raponi, Andrea
T1  - Comet 67P/CG Nucleus Composition and Comparison to Other Comets
JF  - Space science reviews
N2  - We review our current knowledge of comet 67P/Churyumov–Gerasimenko nucleus composition as inferred from measurements made by remote sensing and in-situ instruments aboard Rosetta orbiter and Philae lander. Spectrophotometric properties (albedos, color indexes and Hapke parameters) of 67P/CG derived by Rosetta are discussed in the context of other comets previously explored by space missions. Composed of an assemblage made of ices, organic materials and minerals, cometary nuclei exhibit very dark and red surfaces which can be described by means of spectrophotometric quantities and reproduced with laboratory measurements. The presence of surface water and carbon dioxide ices was found by Rosetta to occur at localized sites where the activity driven by solar input, gaseous condensation or exposure of pristine inner layers can maintain these species on the surface. Apart from these specific areas, 67P/CG’s surface appears remarkably uniform in composition with a predominance of organic materials and minerals. The organic compounds contain abundant hydroxyl group and a refractory macromolecular material bearing aliphatic and aromatic hydrocarbons. The mineral components are compatible with a mixture of silicates and fine-grained opaques, including Fe-sulfides, like troilite and pyrrhotite, and ammoniated salts. In the vicinity of the perihelion several active phenomena, including the erosion of surface layers, the localized activity in cliffs, fractures and pits, the collapse of overhangs and walls, the transfer and redeposition of dust, cause the evolution of the different regions of the nucleus by inducing color, composition and texture changes.
KW  - Comets
KW  - Composition
KW  - Ices
KW  - Organic matter
KW  - Minerals
Y1  - 2019
U6  - https://doi.org/10.1007/s11214-019-0580-3
SN  - 0038-6308
SN  - 1572-9672
VL  - 215
IS  - 19
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Grott, Matthias
A1  - Knollenberg, J.
A1  - Hamm, M.
A1  - Ogawa, K.
A1  - Jaumann, R.
A1  - Otto, Katharina Alexandra
A1  - Delbo, M.
A1  - Michel, Patrick
A1  - Biele, J.
A1  - Neumann, Wladimir
A1  - Knapmeyer, Martin
A1  - Kührt, E.
A1  - Senshu, H.
A1  - Okada, T.
A1  - Helbert, Jorn
A1  - Maturilli, A.
A1  - Müller, N.
A1  - Hagermann, A.
A1  - Sakatani, Naoya
A1  - Tanaka, S.
A1  - Arai, T.
A1  - Mottola, Stefano
A1  - Tachibana, Shogo
A1  - Pelivan, Ivanka
A1  - Drube, Line
A1  - Vincent, J-B
A1  - Yano, Hajime
A1  - Pilorget, C.
A1  - Matz, K. D.
A1  - Schmitz, N.
A1  - Koncz, A.
A1  - Schröder, Stefan E.
A1  - Trauthan, F.
A1  - Schlotterer, Markus
A1  - Krause, C.
A1  - Ho, T-M
A1  - Moussi-Soffys, A.
T1  - Low thermal conductivity boulder with high porosity identified on C-type asteroid (162173) Ryugu
JF  - Nature astronomy
N2  - C-type asteroids are among the most pristine objects in the Solar System, but little is known about their interior structure and surface properties. Telescopic thermal infrared observations have so far been interpreted in terms of a regolith-covered surface with low thermal conductivity and particle sizes in the centimetre range. This includes observations of C-type asteroid (162173) Ryugu1,2,3. However, on arrival of the Hayabusa2 spacecraft at Ryugu, a regolith cover of sand- to pebble-sized particles was found to be absent4,5 (R.J. et al., manuscript in preparation). Rather, the surface is largely covered by cobbles and boulders, seemingly incompatible with the remote-sensing infrared observations. Here we report on in situ thermal infrared observations of a boulder on the C-type asteroid Ryugu. We found that the boulder’s thermal inertia was much lower than anticipated based on laboratory measurements of meteorites, and that a surface covered by such low-conductivity boulders would be consistent with remote-sensing observations. Our results furthermore indicate high boulder porosities as well as a low tensile strength in the few hundred kilopascal range. The predicted low tensile strength confirms the suspected observational bias6 in our meteorite collections, as such asteroidal material would be too frail to survive atmospheric entry7
Y1  - 2019
U6  - https://doi.org/10.1038/s41550-019-0832-x
SN  - 2397-3366
VL  - 3
IS  - 11
SP  - 971
EP  - 976
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Ciarniello, Mauro
A1  - Fulle, Marco
A1  - Raponi, Andrea
A1  - Filacchione, Gianrico
A1  - Capaccioni, Fabrizio
A1  - Rotundi, Alessandra
A1  - Rinaldi, Giovanna
A1  - Formisano, Michelangelo
A1  - Magni, Gianfranco
A1  - Tosi, Federico
A1  - De Sanctis, Maria Cristina
A1  - Capria, Maria Teresa
A1  - Longobardo, Andrea
A1  - Beck, Pierre
A1  - Fornasier, Sonia
A1  - Kappel, David
A1  - Mennella, Vito
A1  - Mottola, Stefano
A1  - Rousseau, Batiste
A1  - Arnold, Gabriele
T1  - Macro and micro structures of pebble-made cometary nuclei reconciled by seasonal evolution
JF  - Nature astronomy
N2  - 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.
KW  - Asteroids, comets and Kuiper belt
KW  - Planetary science
Y1  - 2022
U6  - https://doi.org/10.1038/s41550-022-01625-y
SN  - 2397-3366
VL  - 6
IS  - 5
SP  - 546
EP  - 553
PB  - Nature Research
CY  - Berlin
ER  -