The interior of Comet 67P/C–G; revisiting CONSERT results with the exact position of the Philae lander

Kofman, W.; Zine, Sonia; Hérique, Alain; Rogez, Yves; Jordá, L.; Levasseur-Regourd, A. C.

doi:10.1093/mnras/staa2001

Cited by 22 publications

(21 citation statements)

References 22 publications

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“…The density, together with the average permittivity measured by CONSERT between Rosetta and Philae, suggests a porosity as high as 75%-85% assuming that 67P/C-G consists of a uniform mixture of ice and dust of carbonaceous chondrite type [263]. The volumetric dust/ice ratio is estimated to be 0.4-2.6 [263], and, from a dielectric point of view and at the wavelength scale of CONSERT (3.3 m), the head of the nucleus is quite homogeneous at depths between 25 and 150 m [264,265]. In addition, the surface layer of the nucleus of at least 1 m thickness is more compact than the interior with a porosity of less than 50%, which suggests that it could be a sintered layer [266].…”

Section: Jupiter-family Comet 67p/c-gmentioning

confidence: 97%

Shapes, structures, and evolution of small bodies

Yun

Michel

2021

Astrodyn

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Small bodies are among the best tracers of our Solar System's history. A large number of space missions to small bodies (past and future) offer a unique opportunity to use these bodies as a natural laboratory to study the different processes, mechanical structures, and responses that drive the origin and evolution of small bodies, which are connected to the origin, evolution, and current architecture of the Solar System. Images of small bodies sent by spacecraft have revealed unexpectedly rich and complex geological worlds.In addition to very diverse compositions, small bodies in the Solar System have highly diverse shapes and structures, which reflect both different evolutionary paths and material properties. Furthermore, each individual body has diverse geological features on its surface, which include craters of various sizes and depths, boulders of different sizes and morphologies, lineaments, fractures, pits, signatures of landslides, terraces, and ridges. Such a geological richness could not be detected via ground-based observations, and we are still at the beginning of understanding their significance on the low-gravity surfaces on which they manifest. The combination of space mission data and numerical modeling allows us to enrich our understanding of the origin, evolution, and physical properties of these fascinating bodies. For instance, starting from the shape models, bulk densities, and spin rates determined from space mission data, we can investigate the formation mechanisms that lead to the observed properties of small bodies. We can also infer the interior and mechanical properties (e.g., friction and cohesion) that allow a small body to be structurally stable, as well as its further potential evolution under processes such as a spin rate increase or an impact. Then, considering the various processes that these bodies experience during their evolution, we can investigate how these processes modify their properties and, in turn, how those properties influence the outcome of these processes. This paper reviews our current knowledge of small-body shapes and structures and discusses the various processes that are responsible for their formation and evolution, which can modify the characteristics of the bodies. We separately consider each population of small bodies, although in some cases, such as active asteroids and comets, the distinction between two populations solely in terms of physical properties is not clear. We then summarize the main findings regarding the physical properties of small bodies that have been the target of rendezvous or sample return missions.

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Section: Jupiter-family Comet 67p/c-gmentioning

confidence: 97%

Shapes, structures, and evolution of small bodies

Yun

Michel

2021

Astrodyn

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“…Hadamcik & Levasseur-Regourd 2009;Biele et al 2015;Spohn et al 2015;Kwon et al 2018). The Comet Nucleus Sounding Experiment by Radiowave Transmission (CON-SERT), onboard Rosetta and its Philae lander, indeed provides the evidence of a shallow subsurface of about 20 m depth, less porous and thus denser than the interior of the nucleus (Kofman et al 2020).…”

Section: Conjecture Based On the Observational Evidence In This Studymentioning

confidence: 99%

“…In the following, we use 60 % as a representative porosity value of the dust particles, showing non-fragmentation behaviour (Hornung et al 2016). The retrieved microporosity of the dust particles is lower than the macroscopic porosity of the 67P nucleus of 75-85 % estimated by CONSERT (Kofman et al 2015(Kofman et al , 2020, 65-80 % from the Rosetta/Radio Science Investigation (RSI) (Pätzold et al 2019) and 70-75 % from the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) pre-perihelion observations (Jorda et al 2016). The microporosity is also lower than the macroscopic surface porosity of 87 % derived by the Hapke model (Fornasier et al 2015).…”

Section: Comparison With the Rosetta Observations And Estimation Of T...mentioning

confidence: 99%

VLT spectropolarimetry of comet 67P: Dust environment around the end of its intense Southern summer

Kwon,

Bagnulo,

Markkanen

et al. 2021

Preprint

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Context. A cornucopia of Rosetta and ground-based observational data sheds light on the evolution of the characteristics of dust particles from comet 67P/Churyumov-Gerasimenko (hereafter 67P) with seasons, implying the different dust environments in the source regions on the surface of the comet. Aims. We aim to constrain the properties of the dust particles of 67P and therefrom diagnose the dust environment of its coma and near-surface layer at around the end of the Southern summer of the comet. Methods. We performed spectropolarimetric observations for 67P dust over 4,000-9,000 Å using the ESO/Very Large Telescope in January-March 2016 (phase angle ranging ∼26 • -5 • ). We examined the optical behaviours of the dust, which, together with Rosetta colour data, were used to search for dust evolution with cometocentric distance. Modelling was also conducted to identify the dust attributes compatible with the results. Results. The spectral dependence of the polarisation degree of 67P dust is flatter than found in other dynamical groups of comets in similar observing geometry. The depth of its negative polarisation branch appears to be a bit shallower than in long-period comets and might be getting shallower as 67P repeats its apparitions. Its dust colour shows a change in slope around 5,500 Å, (17.3 ± 1.4) and (10.9 ± 0.6) % (1,000 Å) −1 for shortward and longward of the wavelength, respectively, which are slightly redder but broadly consistent with the average of Jupiter-Family comets. Conclusions. Observations of 67P dust in this study can be attributed to dust agglomerates of ∼100 µm in size detected by Rosetta in early 2016. A porosity of 60 % shows the best match with our polarimetric results, yielding a dust density of ∼770 kg m −3 . Compilation of Rosetta and our data indicates the dust's reddening with increasing nucleus distance, which may be driven by water-ice sublimation as the dust moves out of the nucleus. We estimate the possible volume fraction of water ice in the initially ejected dust as ∼6 % (i.e. the refractory-to-ice volume ratio of ∼14).

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“…Especially small bodies (< 100 km in size), like comets and small asteroids, should not have experienced any strong material stratification. In case of comets, radar measurements indicate a less porous structure at the subsurface on a scale of ten metres (Kofman et al 2020). However, for the uppermost centimetres of the material, which are important in our model, no constraint is given for depthdepending material properties by direct measurements.…”

Section: Future Workmentioning

confidence: 99%

A method to distinguish between micro- and macro-granular surfaces of small Solar System bodies

Bischoff,

Gundlach,

Blum

2021

Preprint

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The surface granularity of small Solar System bodies is diverse through the different types of planetary bodies and even for specific objects it is often not known in detail. One of the physical properties that strongly depends on the surface structure is the surface temperature. In highly porous media with large voids, radiation can efficiently transport heat, whereas more compact, micro-porous structures transport the heat primarily by conduction through the solid material. In this work, we investigate under which conditions a macro-porous surface can be distinguished from a micro-porous one by simply measuring the surface temperature. In our numerical simulations, we included circular and elliptical orbits with and without obliquity and varied the rotation period of the considered objects. We found that daily temperature cycles are rather insensitive to the specific surface granularity. However, the surface temperature at sunrise shows significant dependency on the material structure and this effect becomes even more pronounced when the solar intensity increases. By measuring the sunrise temperature as a function of insolation at noon, a differentiation between micro-and macro-granular surface structures is possible. In this paper, we provide a strategy how remote sensing can be used to derive the surface structure of small Solar System bodies.

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The interior of Comet 67P/C–G; revisiting CONSERT results with the exact position of the Philae lander

Cited by 22 publications

References 22 publications

Shapes, structures, and evolution of small bodies

Shapes, structures, and evolution of small bodies

VLT spectropolarimetry of comet 67P: Dust environment around the end of its intense Southern summer

A method to distinguish between micro- and macro-granular surfaces of small Solar System bodies

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