@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{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{GrottKnollenbergHammetal.2019, author = {Grott, Matthias and Knollenberg, J. and Hamm, M. and Ogawa, K. and Jaumann, R. and Otto, Katharina Alexandra and Delbo, M. and Michel, Patrick and Biele, J. and Neumann, Wladimir and Knapmeyer, Martin and K{\"u}hrt, E. and Senshu, H. and Okada, T. and Helbert, Jorn and Maturilli, A. and M{\"u}ller, N. and Hagermann, A. and Sakatani, Naoya and Tanaka, S. and Arai, T. and Mottola, Stefano and Tachibana, Shogo and Pelivan, Ivanka and Drube, Line and Vincent, J-B and Yano, Hajime and Pilorget, C. and Matz, K. D. and Schmitz, N. and Koncz, A. and Schr{\"o}der, Stefan E. and Trauthan, F. and Schlotterer, Markus and Krause, C. and Ho, T-M and Moussi-Soffys, A.}, title = {Low thermal conductivity boulder with high porosity identified on C-type asteroid (162173) Ryugu}, series = {Nature astronomy}, volume = {3}, journal = {Nature astronomy}, number = {11}, publisher = {Nature Publishing Group}, address = {London}, issn = {2397-3366}, doi = {10.1038/s41550-019-0832-x}, pages = {971 -- 976}, year = {2019}, abstract = {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}, language = {en} } @article{GrottKnollenbergHammetal.2019, author = {Grott, Matthias and Knollenberg, J. and Hamm, M. and Ogawa, K. and Jaumann, R. and Otto, Katharina Alexandra and Delbo, M. and Michel, P. and Biele, J. and Neumann, W. and Knapmeyer, M. and Kuehrt, E. and Senshu, H. and Okada, T. and Helbert, J. and Maturilli, A. and M{\"u}ller, N. and Hagermann, A. and Sakatani, N. and Tanaka, S. and Arai, T. and Mottola, S. and Tachibana, S. and Pelivan, Ivanka and Drube, L. and Vincent, J-B and Yano, H. and Pilorget, C. and Matz, K. D. and Schmitz, N. and Koncz, A. and Schr{\"o}der, S. E. and Trauthan, F. and Schlotterer, M. and Krause, C. and Ho, T-M and Moussi-Soffys, A.}, title = {Low thermal conductivity boulder with high porosity identified on C-type asteroid (162173) Ryugu}, series = {Nature astronomy}, volume = {3}, journal = {Nature astronomy}, number = {11}, publisher = {Nature Publishing Group}, address = {London}, issn = {2397-3366}, doi = {10.1038/s41550-019-0832-x}, pages = {971 -- 976}, year = {2019}, abstract = {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.}, language = {en} }