Modeling of the thermal behavior and of the chemical differentiation of cometary nuclei

Espinasse, S.; Klinger, J.; Ritz, Catherine; Schmitt, Bernard

doi:10.1016/0019-1035(91)90058-2

Cited by 116 publications

(78 citation statements)

References 17 publications

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“…Espinasse et al 1991;Shoshany et al 2002;Guilbert-Lepoutre et al 2011). Based on a fractal porous model of cometary ice, Shoshany et al (2002) propose an analytic expression for the effective thermal conductivity as a function of porosity p (defined as the fraction of the volume occupied by voids), in the form of a temperature-independent correction factor Φ = (1 − p/p c ) 4.1p+0.22 , where p c = 0.7 the porosity at percolation threshold.…”

Section: Thermal Inertia and Dependence With Heliocentric Distancementioning

confidence: 99%

“TNOs are Cool”: A survey of the trans-Neptunian region

Lellouch

Santos-Sanz

Lacerda

et al. 2013

A&A

137

143

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Aims. The goal of this work is to characterize the ensemble thermal properties of the Centaurs / trans-Neptunian population. Methods. Thermal flux measurements obtained with Herschel/PACS and Spitzer/MIPS provide size, albedo, and beaming factors for 85 objects (13 of which are presented here for the first time) by means of standard radiometric techniques. The measured beaming factors are influenced by the combination of surface roughness and thermal inertia effects. They are interpreted within a thermophysical model to constrain, in a statistical sense, the thermal inertia in the population and to study its dependence on several parameters. We use in particular a Monte-Carlo modeling approach to the data whereby synthetic datasets of beaming factors are created using random distributions of spin orientation and surface roughness. Results. Beaming factors η range from values <1 to ∼2.5, but high η values (>2) are lacking at low heliocentric distances (r h < 30 AU). Beaming factors lower than 1 occur frequently (39% of the objects), indicating that surface roughness effects are important. We determine a mean thermal inertia for Centaurs/ TNO of Γ = (2.5 ± 0.5) J m −2 s −1/2 K −1 , with evidence of a trend toward decreasing Γ with increasing heliocentric (by a factor ∼2.5 from 8-25 AU to 41-53 AU). These thermal inertias are 2-3 orders of magnitude lower than expected for compact ices, and generally lower than on Saturn's satellites or in the Pluto/Charon system. Most high-albedo objects are found to have unusually low thermal inertias. Our results suggest highly porous surfaces, in which the heat transfer is affected by radiative conductivity within pores and increases with depth in the subsurface.

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Section: Thermal Inertia and Dependence With Heliocentric Distancementioning

confidence: 99%

“TNOs are Cool”: A survey of the trans-Neptunian region

Lellouch

Santos-Sanz

Lacerda

et al. 2013

A&A

137

143

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“…We thus adopted the approach developed by Espinasse et al (1989Espinasse et al ( , 1991 rather than more up-to-date concepts which have been developed since that time (see for example Tancredi et al 1994;Enzian et al 1997).…”

Section: General Assumptionsmentioning

confidence: 99%

“…Hence, in that case, the gas is close to saturation and so automatically compensates for the local loss or gain of gas due to gas diffusion towards the surface. We can then take a sublimation/recondensation rate equal to (Espinasse et al 1991): (2) where δt is the time step of our simulation, and Π the porosity.…”

Section: Physical Processesmentioning

confidence: 99%

The physico-chemical history of Falling Evaporating Bodies aroundβPictoris: investigating the presence of volatiles

Karmann

Beust

Klinger

2001

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Abstract. Transient spectral absorption events have been monitored for many years toward the star β Pictoris and have been interpreted as resulting from the transit across the line of sight of evaporating comet-sized bodies (Falling Evaporating Bodies, or FEBs). The model shows that these bodies come from circular orbits at > ∼ 4 AU, becoming star-grazers due to planetary perturbations. The physics of the evaporation of those bodies is widely influenced by their physico-chemical properties, especially the presence of volatile matter. We investigate here this question from a modeling point of view, adapting for that case the models designed for solar comets. We simulate the physico-chemical evolution of the FEB progenitors on circular orbits for a time comparable to the supposed age of β Pic, and constrain the quantity of volatiles present in them in relationship with its age and to the semi-major axis of the orbits. We also constrain this semi-major axis by investigating its influence on the dynamical model of FEB generation by planetary perturbations, and show that it is probably less than ∼10 AU. Finally, we show that demanding the FEB progenitors to be icy in a major part of their volume at those distances is probably an unrealistic constraint, and that they more likely look like asteroids with perhaps a small icy nucleus rather than fully icy comets. This result leads to a revision of the FEB evaporation model that has been assumed up to now.

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“…H x is the molar latent heat of sublimation of ice x (J mol −1 ) and Q cr x (mol m −3 s −1 ) and Y cr are the rate of moles of gas x and the power per unit volume released during the crystallization process of amorphous water ice respectively (Espinasse et al 1991;Orosei et al 1999). Q x is the rate of volatile molecule x (mol m −3 s −1 ) that sublimates/condenses in the pores of the matrix, and is given by the gas diffusion equation that describes the diffusion of gas through the porous matrix for each molecule x:…”

Section: Nucleus Modelmentioning

confidence: 99%

On the stability of clathrate hydrates in comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen

Marboeuf

Mousis

Petit

et al. 2010

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Context. For several years, Jupiter-family comets have been the targets of spacecraft missions whose aims are to determine the comets' composition, structure, and physical properties. The Rosetta mission is currently flying towards comet 67P/Churyumov Gerasimenko for a rendezvous in August 2014 and comet 46P/Wirtanen is considered for a rendezvous in 2021 with the PriME (Primitive Material Explorer) mission, which is currently proposed to NASA. Aims. Here we investigate the stability conditions of clathrate hydrates within the comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen by considering an initial mixture of amorphous H 2 O with CO, CO 2 , CH 4 , and H 2 S in the nuclei. Methods. We use a one-dimensional nucleus model, which considers an initially homogeneous sphere composed of a predefined porous mixture of ices and dust in specified proportions and describes heat transmission, gas diffusion, sublimation/recondensation of volatiles within the nucleus, water ice phase transition, dust release, and mantle formation. Results. We show that stability conditions of multiple guest clathrates are permanently reached in the subsurface of both comets, and in a broader manner in the subsurface of all short period comets. The thickness of the stability zone of the clathrate slightly oscillates with time as a function of the heliocentric distance, but never vanishes. When comets approach perihelion, our calculations suggest that clathrate layers, which are located closer to the nucleus surface, may destabilize before amorphous ice is tranformed into crystalline ice.

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Modeling of the thermal behavior and of the chemical differentiation of cometary nuclei

Cited by 116 publications

References 17 publications

“TNOs are Cool”: A survey of the trans-Neptunian region

“TNOs are Cool”: A survey of the trans-Neptunian region

The physico-chemical history of Falling Evaporating Bodies aroundβPictoris: investigating the presence of volatiles

On the stability of clathrate hydrates in comets 67P/Churyumov-Gerasimenko and 46P/Wirtanen

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