Comet 67P/Churyumov–Gerasimenko preserved the pebbles that formed planetesimals

Fulle, M.; Corte, Vincenzo Della; Rotundi, A.; Rietmeijer, Frans J. M.; Green, Simon; Weissman, P. R.; Accolla, M.; Colangeli, L.; Ferrari, M.; Ivanovski, S.; Moreno, J. J. Lopez; Epifani, E. Mazzotta; Morales, R.; Ortiz, J. L.; Palomba, E.; Palumbo, P.; Rodriguez, J.; Sordini, R.; Захаров, Владимир

doi:10.1093/mnras/stw2299

Cited by 124 publications

(53 citation statements)

References 39 publications

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“…Comets are highly porous objects (∼70%-80% porosity Blum et al 2006;Kofman et al 2015;Fulle et al 2016;Pätzold et al 2016), and are composed of refractory dust and ices of different volatiles. Their bulk density is very low, about 0.5 g cm −3 (Blum et al 2006;A'Hearn 2011;Sierks et al 2015;Pätzold et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

Lorek

Lacerda

Blum

2018

A&A

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Context. Comet formation by gravitational instability requires aggregates that trigger the streaming instability and cluster in pebble-clouds. These aggregates form as mixtures of dust and ice from (sub-)micrometre-sized dust and ice grains via coagulation in the solar nebula. Aim. We investigate the growth of aggregates from (sub-)micrometre-sized dust and ice monomer grains. We are interested in the properties of these aggregates: whether they might trigger the streaming instability, how they compare to pebbles found on comets, and what the implications are for comet formation in collapsing pebble-clouds. Methods. We used Monte Carlo simulations to study the growth of aggregates through coagulation locally in the comet-forming region at 30 au. We used a collision model that can accommodate sticking, bouncing, fragmentation, and porosity of dust- and ice-mixed aggregates. We compared our results to measurements of pebbles on comet 67P/Churyumov-Gerasimenko. Results. We find that aggregate growth becomes limited by radial drift towards the Sun for 1 μm sized monomers and by bouncing collisions for 0.1 μm sized monomers before the aggregates reach a Stokes number that would trigger the streaming instability (Stmin). We argue that in a bouncing-dominated system, aggregates can reach Stmin through compression in bouncing collisions if compression is faster than radial drift. In the comet-forming region (~30 au), aggregates with Stmin have volume-filling factors of ~10−2 and radii of a few millimetres. These sizes are comparable to the sizes of pebbles found on comet 67P/Churyumov-Gerasimenko. The porosity of the aggregates formed in the solar nebula would imply that comets formed in pebble-clouds with masses equivalent to planetesimals of the order of 100 km in diameter.

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Section: Introductionmentioning

confidence: 99%

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

Lorek

Lacerda

Blum

2018

A&A

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“…In addition, its mafic composition and its size distribution make it suitable for radar investigations dedicated to Mars [e.g., Mattei et al, 2014] and asteroids [e.g., Palmer et al, 2015]. It has also a porous structure [Brouet et al, 2015], which can be interesting to approach, for example, the fluffy structure of the cometary dust, estimated from in situ measurements [e.g., Fulle et al, 2000Fulle et al, , 2016 and from remote light scattering observations [e.g., Levasseur-Regourd et al, 2009]. The method used for the permittivity measurements over the frequency range of 50 MHz to 2 GHz is then defined.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the permittivity of controlled porous water ice-dust mixtures to support the radar exploration of icy bodies

Brouet

Neves

Sabouroux

et al. 2016

J. Geophys. Res. Planets

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The internal properties of porous and icy bodies in the solar system can be investigated by ground‐penetrating radars (GPRs), like the COmet Nucleus Sounding Experiment by Radiowave Transmission instrument on board the Rosetta spacecraft which has sounded the interior of the nucleus of comet 67P/Churyumov‐Gerasimenko. Accurate constraints on the permittivity of icy media are needed for the interpretation of the data. We report novel permittivity measurements performed on water ice samples and icy mixtures with porosities in the 31–91% range. The measurements have been performed between 50 MHz and 2 GHz with a coaxial cell on a total of 38 samples with a good reproducibility. We used controlled procedures to produce fine‐grained and coarse‐grained ice samples with a mean diameter of 4.5 μm and 67 μm, respectively, and to prepare icy mixtures. The JSC‐1A lunar regolith simulant was used as the dust component in the mixtures. The results are focused on the real‐part ε′ of the permittivity, which constrains the phase velocity of the radio waves in low‐loss media. The values of ε′ show a nondispersive behavior and are within the range of 1.1 to 2.7. They decrease with the increasing porosity Φ according to E(1 − Φ), with E equal to about 3.13 for pure water ice, and in the 3.8–7.5 range for ice‐dust mixtures with a dust‐to‐ice volumetric ratio in the 0.1–2.8 range, respectively. These measurements are also relevant for radiometers operating in the millimeter‐submillimeter domains, as suggested by the nondispersive behavior of the mixtures and of the pure components.

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“…How real is a global layered structure of comets (Penasa et al, 2017;Thomas et al, 2015;Fulle et al, 2016)? Do the structures on the surface of comet 67P detected by the panoramic camera onboard the Philae probe actually represent agglomerates of primordial pebbles (Poulet et al, 2016;Fulle et al, 2016a)? In which way does a high ratio of the refractory component and ices in comet 67P (according to different estimates, it ranges from 4±2 (Rotundi et al, 2015) to 8.5 (Fulle et al, 2016a)) agree with the composition of a protoplanetary nebula in the formation region of comets?…”

Section: Discussionmentioning

confidence: 99%

“…The porosity value depends on both the volume density and the composition of the cometary material. For the nucleus of comet 67P, all of the independent estimates yield the porosity value larger than 70%: 72−74% (Patzold et al, 2016), 71±2% (Davidsson et al, 2016), and 71±8% (Fulle et al, 2016a). The values obtained for the nucleus of comet 67P are consistent with the corresponding quantities for comet 9P/Tempel 1 estimated from the results of the Deep Impact space mission: the density is 400 kg/m3 (Richardson et al, 2007), and the porosity is 75−88% (Ernst and Schultz, 2007).…”

Section: Data Of the Rosetta Space Missionmentioning

confidence: 99%

Dynamics and Origin of Comets: New Problems Appeared after the Rosetta Space Mission

Emel’yanenko

2018

Sol Syst Res

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The data obtained in the recent Rosetta space mission to comet 67P/Churyumov-Gerasimenko have had a profound impact on the understanding of the nature of comets. In addition to revising the notions on the physical properties and structure of comets, this addresses dynamical aspects of the formation of the observed cometary populations (short-and long-period comets, Centaurs, trans-Neptunian objects, and Oort-cloud objects). In the review, we discuss new problems that have appeared in the theory of dynamical evolution and origin of comets due to the Rosetta mission. POPULATIONS OF COMETS IN THE SOLAR SYSTEMAlong with visible features, especially the presence of a coma in the objects of the inner Solar system, there are two characteristic features in comets that set them apart from the other Solar system bodies. First, comets move along high-eccentricity orbits; and, second, there are often substantial nongravitational effects in their motion. In the mid last century, attempts to explain these features resulted in two remarkable achievements in understanding the nature of comets. It was found that comets with near-parabolic orbits exhibit a concentration of values w = 1/a (where a is the semimajor axis of an orbit) in a range of w<10 -4 au -1 . This led J.H. Oort to a concept of a cometary cloud on the periphery of the Solar system (Oort, 1950); this cloud now bears his name. The nongravitational effects were explained by the model, supposing the presence of a solid rotating nucleus composed of frozen volatile compounds, mainly water with admixed dust (Whipple, 1950). In our days, the Oort cloud model and the cometary nucleus model have been substantially modified and improved; however, in general, these achievements provided a basis for the approaches currently developed in the studies of cometary dynamics and physics.While Oort (1950) had only 14 sufficiently exact orbits with w<10 -4 au -1 at his disposal, now the number of such orbits has increased substantially. For near-parabolic comets with a perihelion distance q <5 au, typical changes in the value of w due to the planetary perturbations for one passage through the planetary region considerably exceed 10 -4 au -1 (Fernandez,1981; Emel'yanenko, 1992). Consequently, there is no doubt that the majority of observed comets with the Oort-cloud values of w are "new": they enter near-Earth space for the first time after long being in orbits with large perihelion distances. As shown in papers by Duncan et al. (1987), Dones et al. (2004), andEmel'yanenko et al. (2007), the Oort cloud is a natural result of a long dynamical evolution of objects ejected from the planetary region. The main features in the orbit distribution of the Oort cloud weakly depend on dynamical characteristics specific to the bodies at the first stages of the Solar system formation and are mainly determined by the long-term influence of planetary, stellar, and galactic perturbations. Due to the effects of stellar and galactic perturbations, the orbits of most objects are currently far from the pl...

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Comet 67P/Churyumov–Gerasimenko preserved the pebbles that formed planetesimals

Cited by 124 publications

References 39 publications

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

Characterization of the permittivity of controlled porous water ice-dust mixtures to support the radar exploration of icy bodies

Dynamics and Origin of Comets: New Problems Appeared after the Rosetta Space Mission

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