Dust release and tensile strength of the non-volatile layer of cometary nuclei

Skorov, Yu. V.; Blum, Jürgen

doi:10.1016/j.icarus.2012.01.012

Cited by 146 publications

(196 citation statements)

References 43 publications

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“…Experimental work by Weidling et al (2009) and Güttler et al (2009) also showed that the volume-filling factor of silica pebbles acquires a value of ∼0.4 after experiencing many bouncing collisions. The filling factor of the comet, φ c , is then the product of both: φ c = φ p × φ ≈ 0.24 (Skorov & Blum 2012). Comets are thus expected to be porous bodies, which agrees with recent density measurements and estimates (e.g.…”

Section: Introductionsupporting

confidence: 86%

“…According to Skorov & Blum (2012), the packing fraction is φ P ≈ 0.6, which falls in the range between random loose packing (RLP) with φ P = 0.55 and random close packing (RCP) with φ P = 0.64.…”

Section: Dust-to-ice Ratiomentioning

confidence: 99%

“…As argued by Skorov & Blum (2012) and Blum et al (2014), the benefits of SI as a mechanism for forming comets is that it bypasses growth barriers, while the collision speeds of pebbles in a collapsing cloud also remain low, at most the escape velocity of the cloud. Hence, pebble fragmentation plays only a minor role, if at all, and the dominant collision-type is bouncing.…”

Section: Introductionmentioning

confidence: 99%

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Comet formation in collapsing pebble clouds

Lorek

Gundlach

Lacerda

et al. 2016

A&A

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Context. Comets are remnants of the icy planetesimals that formed beyond the ice line in the solar nebula. Growing from μm-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation. Aims. We study the collisional compression of silica, ice, and silica/ice-mixed pebbles during gravitational collapse of pebble clouds. Using the initial volume-filling factor and the dust-to-ice ratio of the pebbles as free parameters, we constrain the dust-to-ice mass ratio of the formed comet and the resulting volume-filling factor of the pebbles, depending on the cloud mass. Methods. We use the representative particle approach, which is a Monte Carlo method, to follow cloud collapse and collisional evolution of an ensemble of ice, silica, and silica/ice-mixed pebbles. Therefore, we developed a collision model which takes the various collision properties of dust and ice into account. We study pebbles with a compact size of 1 cm and vary the initial volume-filling factors, φ 0 , ranging from 0.001 to 0.4. We consider mixed pebbles as having dust-to-ice ratios between 0.5 and 10. We investigate four typical cloud masses, M, between 2.6 × 10 14 (very low) and 2.6 × 10 23 g (high). Results. Except for the very low-mass cloud (M = 2.6 × 10 14 g), silica pebbles are always compressed during the collapse and attain volume-filling factors in the range from φ V ≈ 0.22 to 0.43, regardless of φ 0 . Ice pebbles experience no significant compression in very low-mass clouds. They are compressed to values in the range φ V ≈ 0.11 to 0.17 in low-and intermediate-mass clouds (M = 2.6 × 10 17 −2.6 × 10 20 g); in high-mass clouds (M = 2.6 × 10 23 g), ice pebbles end up with φ V ≈ 0.23. Mixed pebbles obtain filling factors in between the values for pure ice and pure silica. We find that the observed cometary density of ∼0.5 g cm −3 can only be explained by either intermediate-or high-mass clouds, regardless of φ 0 , and also by either very low-or low-mass clouds for initially compact pebbles. In any case, the dust-to-ice ratio must be in the range of between 3 ξ 9 to match the observed bulk properties of comet nuclei.

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Section: Introductionsupporting

confidence: 86%

Section: Dust-to-ice Ratiomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comet formation in collapsing pebble clouds

Lorek

Gundlach

Lacerda

et al. 2016

A&A

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“…Thus the thermal conductivity retrieved from observations might be treated as an upper limit for the solid conductivity of the surface layer. We assume that the solid conductivities of the dust crust and the ice-dust mixture are the same and that the material porosity is constant everywhere (as in Skorov & Blum 2012). In addition to the solid conductivity, the radiative conductivity as a part of the effective conductivity is considered in the model (Gundlach & Blum 2012).…”

Section: Depth Of Super-volatiles: Model Descriptionmentioning

confidence: 99%

“…If we assume that the pore diameter is about one millimeter and the tortuosity is about 3 (see references in Skorov & Blum 2012), then the expected escaping time is a few days. At the same time, diffusive resistance of the overlying layer is so high (it is proportional to the ratio of the depth to the pore diameter) that only a fraction of 100 ppm of sublimating molecules escapes, which means that the effective mass loss is very low.…”

Section: Transient Processes In a Gas-dust-ice Layermentioning

confidence: 99%

A model of short-lived outbursts on the 67P from fractured terrains

Skorov

Rezac

Hartogh

et al. 2016

A&A

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Aims. We develop a physical model to explain the potent outbursts that occurred in the fractured terrain of comet 67P near perihelion, and predict its temporal characteristics. Methods. The feasibility of the proposed mechanism is studied using a numerical model accounting for the relevant microscopic/macroscopic processes. We rely on the thermophysical, compositional, and geo-morphological data from the published measurements of respective instruments on board Rosetta. Results. The key idea of this novel mechanism is built around observations of fractures/cracks in the region of interest. It is argued that as the stresses on the nucleus increased during the perihelion approach, a crack deepening event occurred reaching the deeper material containing super-volatile ices in equilibrium with the surrounding. This sudden opening lead to a violent sublimation of the super-volatile ices. The time scales and mass release of this process are modeled and reported. In our modeling we pay attention to the question of the existence of super-volatile ices in the deeper interior for a long time, and the thermal equilibrium in the interior. Conclusions. The deepening of pre-existing cracks (fracture) into the material containing highly volatile ices can explain the observed outburst features. The sudden disequilibration of the steady-state reservoir of highly volatile ices results in a violent release of gas and dust. The proposed mechanism also explains the rapid shut down of this activity in accordance with the observations. The proposed mechanism is independent of solar illumination history of a given region, or the pre-existance of large sealed nucleus cavities.

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Ejection of large particles from cometary nuclei in the shape of prolate ellipsoids

Gronkowski

Wesołowski

2017

Astron Nachr

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The ejection of cometary grains from comets is examined. It is assumed that cometary grains are chunks of ice-dust material. We focus on cometary nuclei in the shape of prolate ellipsoids. Two mechanisms are considered. The first one is the drag acting on the motionless grains lying on the surface of a comet's nucleus. It is a consequence of the cometary ice's gentle sublimation. The second one is related to the cometary jet-like phenomenon. This mechanism is associated with the rapid flow of gas streams into space from subsurface cavities in a comet's nucleus through narrow gaps and channels. The different elongations of ellipsoidal nuclei are examined. The formula for the maximum radius of grain that can be lifted up from the comet's nucleus is derived. The obtained algorithm takes into account the different cometo-centric latitudes of places from which the cometary grains are ejected. We show that for a fixed mass of nucleus the maximum size of grains is an increasing function of nuclear flattening. Numerical simulation is carried out for a large range of assumed cometary parameters. The obtained results are in good agreement with the observations of the Comet 103P/Hartley carried out by the Deep Impact spacecraft.

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Dust release and tensile strength of the non-volatile layer of cometary nuclei

Cited by 146 publications

References 43 publications

Comet formation in collapsing pebble clouds

Comet formation in collapsing pebble clouds

A model of short-lived outbursts on the 67P from fractured terrains

Ejection of large particles from cometary nuclei in the shape of prolate ellipsoids

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