Two independent and primitive envelopes of the bilobate nucleus of comet 67P

Massironi, Matteo; Simioni, Emanuele; Marzari, F.; Cremonese, G.; Giacomini, L.; Pajola, M.; Jordá, L.; Naletto, G.; Lowry, S. C.; El‐Maarry, M. R.; Preusker, Frank; Scholten, F.; Sierks, H.; Barbieri, C.; Lamy, Philippe; Rodrigo, R.; Koschny, D.; Rickman, H.; Keller, H. U.; A’Hearn, Michael F.; Agarwal, Jessica; Auger, Anne; Barucci, M. A.; Bertaux, J.; Bertini, Ivano; Besse, S.; Bodewits, Dennis; Capanna, Claire; Deppo, Vania Da; Davidsson, B.; Debei, S.; Cecco, M. De; Ferri, F.; Fornasier, S.; Fulle, M.; Gaskell, R. W.; Groussin, O.; Gutiérrez, P. J.; Güttler, C.; Hviid, S. F.; Ip, W.-H.; Knollenberg, J.; Kovács, Gábor; Kramm, R.; Kührt, Ekkehard; Küppers, M.; Forgia, Fiorangela La; Lara, L. M.; Lazzarin, M.; Lin, Z.-Y.; Moreno, J. J. Lopez; Magrin, S.; Michalik, H.; Mottola, S.; Oklay, N.; Pommerol, Antoine; Thomas, N.; Tubiana, C.; Vincent, J. B.

doi:10.1038/nature15511

Cited by 151 publications

(113 citation statements)

References 21 publications

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“…We recognized fractures in the Abydos region that suggest a brittle nature of the outcropping material and that often cut across strata heads. The evidence of these parallel linear features in the region agrees with the scenario that stratification is a dominant structural aspect of 67P throughout its entire bilobed shape (Massironi et al 2015). As explained in Massironi et al (2015), the comet stratification shows that the two lobes are the expression of two independent objects, perhaps formed as pebble-pile planetesimals, that are evidently characterized by onion-like stratification that is several hundred meters thick.…”

Section: Discussionsupporting

confidence: 71%

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Lucchetti

Cremonese

Jordá

et al. 2015

A&A

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Context. On 12 November 2014, the European mission Rosetta delivered the Philae lander on the nucleus of comet 67P/ChuryumovGerasimenko (67P). After the first touchdown, the lander bounced three times before finally landing at a site named Abydos. Aims. We provide a morphologically detailed analysis of the Abydos landing site to support Philae's measurements and to give context for the interpretation of the images coming from the Comet Infrared and Visible Analyser (CIVA) camera system onboard the lander. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 6 December 2014 to perform the analysis of the Abydos landing site, which provided the geomorphological map, the gravitational slope map, the size-frequency distribution of the boulders. We also computed the albedo and spectral reddening maps.Results. The morphological analysis of the region could suggest that Philae is located on a primordial terrain. The Abydos site is surrounded by two layered and fractured outcrops and presents a 0.02 km 2 talus deposit rich in boulders. The boulder size frequency distribution gives a cumulative power-law index of −4.0 + 0.3/−0.4, which is correlated with gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. The average value of the albedo is 5.8% at λ 1 = 480.7 nm and 7.4% at λ 2 = 649.2 nm, which is similar to the global albedos derived by OSIRIS and CIVA, respectively.

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Section: Discussionsupporting

confidence: 71%

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Lucchetti

Cremonese

Jordá

et al. 2015

A&A

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“…Sierks et al 2015;Hässig et al 2015;Capaccioni et al 2015). Based on this data, it has been suggested that its structure is pristine and was formed in the early stages of the solar system (Massironi et al 2015), possibly by low velocity accretionary collisions (Jutzi & Asphaug 2015). What is less clear is whether or not a structure like comet 67P would have been able to survive until today.…”

Section: Introductionmentioning

confidence: 99%

How primordial is the structure of comet 67P?

Jutzi

Benz

Τόλιου

et al. 2016

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Context. There is an active debate about whether the properties of comets as observed today are primordial or, alternatively, if they are a result of collisional evolution or other processes. Aims. We investigate the effects of collisions on a comet with a structure like 67P/Churyumov-Gerasimenko (67P). We develop scaling laws for the critical specific impact energies Q reshape required for a significant shape alteration. These are then used in simulations of the combined dynamical and collisional evolution of comets in order to study the survival probability of a primordially formed object with a shape like 67P. Although the focus of this work is on a structure of this kind, the analysis is also performed for more generic bi-lobe shapes, for which we define the critical specific energy Q bil . The simulation outcomes are also analyzed in terms of impact heating and the evolution of the porosity. Methods. The effects of impacts on comet 67P are studied using a state-of-the-art smooth particle hydrodynamics shock physics code. In the 3D simulations, a publicly available shape model of 67P is applied and a range of impact conditions and material properties are investigated. The resulting critical specific impact energy Q reshape (as well as Q bil for generic bi-lobe shapes) defines a minimal projectile size which is used to compute the number of shape-changing collisions in a set of dynamical simulations. These simulations follow the dispersion of the trans-Neptunian disk during the giant planet instability, the formation of a scattered disk, and produce 87 objects that penetrate into the inner solar system with orbits consistent with the observed JFC population. The collisional evolution before the giant planet instability is not considered here. Hence, our study is conservative in its estimation of the number of collisions. Results. We find that in any scenario considered here, comet 67P would have experienced a significant number of shape-changing collisions, if it formed primordially. This is also the case for generic bi-lobe shapes. Our study also shows that impact heating is very localized and that collisionally processed bodies can still have a high porosity. Conclusions. Our study indicates that the observed bi-lobe structure of comet 67P may not be primordial, but might have originated in a rather recent event, possibly within the last 1 Gy. This may be the case for any kilometer-sized two-component cometary nuclei.

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“…In the first report of the OSIRIS science imaging results, Sierks et al (2015) suggested that the nucleus of 67P/Churyumov-Gerasimenko (67P hereafter) could be just one single monolith (see also Thomas et al 2015). Subsequently, Massironi et al (2015), showed that a contact binary model with the two lobes being completely different entities or cometesimals could be an explanation (see also Rickman et al 2015;Davidsson et al 2016;El-Maarry et al 2015a). Similar scenarios may be proposed for the dumb-bell shaped structures of comet 103P/Hartley 2, comet 1P/Halley and comet 19P/Borrelly even though the shapes of comet 9P/Tempel 1 and 81P/Wild 2 are certainly more monolithic.…”

Section: Introductionmentioning

confidence: 99%

Physical properties and dynamical relation of the circular depressions on comet 67P/Churyumov-Gerasimenko

Lai

Lee

et al. 2016

A&A

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Aims. We aim to characterize the circular depressions of comet 67P/Churyumov-Gerasimenko and investigate whether such surface morphology of a comet nucleus is related to the cumulative sublimation effect since becoming a Jupiter family comet (JFC). Methods. The images from the Rosetta/OSIRIS science camera experiment are used to construct size frequency distributions of the circular depression structures on comet 67P and they are compared with those of the JFCs 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2. The orbital evolutionary histories of these comets over the past 100 000 yr are analyzed statistically and compared with each other. Results. The global distribution of the circular depressions over the surface of 67P is charted and classified. Descriptions are given to the characteristics and cumulative size frequency distribution of the identified features. Orbital statistics of the JFCs visited by spacecraft are derived. Conclusions. The size frequency distribution of the circular depressions is found to have a similar power law distribution to those of 9P/Tempel 1 and 81P/Wild 2. This might imply that they could have been generated by the same process. Orbital integration calculation shows that the surface erosion histories of 81P/Wild 2, and 9P/Tempel 1 could be shorter than those of 67P, 103 P/Hartley 2 and 19P/Borrelly. From this point of view, the circular depressions could be dated back to the pre-JFC phase or the transneptunian phase of these comets. The north-south asymmetry in the distribution of the circular depressions could be associated with the heterogeneous structure of the nucleus of comet 67P and/or the solar insolation history.

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Two independent and primitive envelopes of the bilobate nucleus of comet 67P

Cited by 151 publications

References 21 publications

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

Characterization of the Abydos region through OSIRIS high-resolution images in support of CIVA measurements

How primordial is the structure of comet 67P?

Physical properties and dynamical relation of the circular depressions on comet 67P/Churyumov-Gerasimenko

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