TY  - JOUR
A1  - Tubiana, C.
A1  - Rinaldi, G.
A1  - Guettler, C.
A1  - Snodgrass, C.
A1  - Shi, X.
A1  - Hu, X.
A1  - Marschall, R.
A1  - Fulle, M.
A1  - Bockeele-Morvan, D.
A1  - Naletto, G.
A1  - Capaccioni, F.
A1  - Sierks, H.
A1  - Arnold, G.
A1  - Barucci, M. A.
A1  - Bertaux, J-L
A1  - Bertini, I
A1  - Bodewits, D.
A1  - Capria, M. T.
A1  - Ciarniello, M.
A1  - Cremonese, G.
A1  - Crovisier, J.
A1  - Da Deppo, V
A1  - Debei, S.
A1  - De Cecco, M.
A1  - Deller, J.
A1  - De Sanctis, M. C.
A1  - Davidsson, B.
A1  - Doose, L.
A1  - Erard, S.
A1  - Filacchione, G.
A1  - Fink, U.
A1  - Formisano, M.
A1  - Fornasier, S.
A1  - Gutierrez, P. J.
A1  - Ip, W-H
A1  - Ivanovski, S.
A1  - Kappel, David
A1  - Keller, H. U.
A1  - Kolokolova, L.
A1  - Koschny, D.
A1  - Krueger, H.
A1  - La Forgia, F.
A1  - Lamy, P. L.
A1  - Lara, L. M.
A1  - Lazzarin, M.
A1  - Levasseur-Regourd, A. C.
A1  - Lin, Z-Y
A1  - Longobardo, A.
A1  - Lopez-Moreno, J. J.
A1  - Marzari, F.
A1  - Migliorini, A.
A1  - Mottola, S.
A1  - Rodrigo, R.
A1  - Taylor, F.
A1  - Toth, I
A1  - Zakharov, V
T1  - Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet. Aims. We aim to characterize the spatial distribution of dust, H2O, and CO2 gas in the inner coma. To do this, we performed a quantitative analysis of the release of dust and gas and compared the observed H2O production rate with the rate we calculated using a thermophysical model. Methods. For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H2O emission band), and 4200 nm (CO2 emission band). We measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center. Results. The spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO2 is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0 degrees subsolar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO2 production. An excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270 degrees-50 degrees). A drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50 degrees-90 degrees). Possible explanations of these observations are presented and discussed.
KW  - comets: general
KW  - comets: individual: 67P/Churyumov-Gerasimenko
KW  - methods: data analysis
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201834869
SN  - 1432-0746
VL  - 630
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Rinaldi, G.
A1  - Formisano, M.
A1  - Kappel, David
A1  - Capaccioni, F.
A1  - Bockelee-Morvan, D.
A1  - Cheng, Y-C
A1  - Vincent, J-B
A1  - Deshapriya, P.
A1  - Arnold, G.
A1  - Capria, M. T.
A1  - Ciarniello, M.
A1  - De Sanctis, M. C.
A1  - Doose, L.
A1  - Erard, S.
A1  - Federico, C.
A1  - Filacchione, G.
A1  - Fink, U.
A1  - Leyrat, C.
A1  - Longobardo, A.
A1  - Magni, G.
A1  - Mighorini, A.
A1  - Mottola, S.
A1  - Naletto, G.
A1  - Raponi, A.
A1  - Taylor, F.
A1  - Tosi, F.
A1  - Tozzi, G. P.
A1  - Salatti, M.
T1  - Analysis of night-side dust activity on comet 67P observed by VIRTIS-M
BT  - a new method to constrain the thermal inertia on the surface
JF  - Astronomy and astrophysics : an international weekly journal
N2  - 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.
KW  - comets: general
KW  - comets: individual: 67P/Churyumov-Gerasimenko
KW  - infrared: planetary systems
Y1  - 2019
U6  - https://doi.org/10.1051/0004-6361/201834907
SN  - 1432-0746
VL  - 630
PB  - EDP Sciences
CY  - Les Ulis
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, P.
A1  - Biele, J.
A1  - Neumann, W.
A1  - Knapmeyer, M.
A1  - Kuehrt, E.
A1  - Senshu, H.
A1  - Okada, T.
A1  - Helbert, J.
A1  - Maturilli, A.
A1  - Müller, N.
A1  - Hagermann, A.
A1  - Sakatani, N.
A1  - Tanaka, S.
A1  - Arai, T.
A1  - Mottola, S.
A1  - Tachibana, S.
A1  - Pelivan, Ivanka
A1  - Drube, L.
A1  - Vincent, J-B
A1  - Yano, H.
A1  - Pilorget, C.
A1  - Matz, K. D.
A1  - Schmitz, N.
A1  - Koncz, A.
A1  - Schröder, S. E.
A1  - Trauthan, F.
A1  - Schlotterer, M.
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  - 2020
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  -