Aggregation of grains in space

Arrhenius, Gustaf; Asunmaa, S. K.

doi:10.1007/bf00581731

Cited by 20 publications

(2 citation statements)

References 29 publications

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“…Arrhenius & Asunmaa 1973) indicate large-scale radial mixing of disc material between hot inner and cool outer disc regions during the early stages of planetary system formation. Our calculations have shown that the radial mixing in protoplanetary discs is driven by two different physical mechanisms, by (i) turbulent mixing, which is already discussed by Morfill (1983), preceding papers in the present series and Bockelée- Morvan et al (2002), and (ii) by large-scale meridional flows present in α-discs, which are discussed in this paper.…”

Section: Discussionmentioning

confidence: 99%

Radial mixing in protoplanetary accretion disks

Keller

Gail

2004

A&A

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Abstract. The presence of crystalline dust materials in the outer, cold regions of protoplanetary accretion discs requires conditions for their formation, which are typical for the inner, warm regions of the disc. This suggests the existence of a mechanism that allows an efficient, outward-directed radial transport of material in accretion discs. Higher order analytical calculations, as well as numerical simulations reveal meridional flow structures in α-discs, which exhibit outflow of matter in regions near the disc midplane and may play a significant role in radial mixing in protoplanetary accretion discs. We present an analytical, isothermal model for the large-scale meridional flow pattern in an α-disc, verifying the approximations which it is based on by means of a 2-D numerical computation. The solution for the flow structure obtained is used for calculating the transport of a tracer in accretion discs in combination with diffusional mixing. The impact of radial flows on mixing of tracers is compared to the height-averaged inflow solution of the standard one-zone approximation.

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Section: Discussionmentioning

confidence: 99%

Radial mixing in protoplanetary accretion disks

Keller

Gail

2004

A&A

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“…Dust grains from the protoplanetary disk collide, stick together and form clumps that progressively grow in size and mass (Weidenschilling 1980). Sticking of initially micronsized grains has been hypothesized to occur via a range of processes that includes electrostatic attraction (Marshall and Cuzzi 2001), aerodynamical sticking (Wurm et al 2001), impact melting (Lewis 2004) and/or vacuum welding (Arrhenius and Asunmaa 1973). As material accumulated, more planetesimal surface area became available to add material so the process accelerated.…”

Section: Protoplanet Accretionmentioning

confidence: 99%

Origin, Internal Structure and Evolution of 4 Vesta

et al. 2011

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Asteroid 4 Vesta is the only preserved intact example of a large, differentiated protoplanet like those believed to be the building blocks of terrestrial planet accretion. Vesta accreted rapidly from the solar nebula in the inner asteroid belt and likely melted due to heat released due to the decay of 26 Al. Analyses of meteorites from the howardite-eucritediogenite (HED) suite, which have been both spectroscopically and dynamically linked to Vesta, lead to a model of the asteroid with a basaltic crust that overlies a depleted peridotitic mantle and an iron core. Vesta's crust may become more mafic with depth and might have been intruded by plutons arising from mantle melting. Constraints on the asteroid's moments of inertia from the long-wavelength gravity field, pole position and rotation, informed by bulk composition estimates, allow tradeoffs between mantle density and core size; cores of up to half the planetary radius can be consistent with plausible mantle compositions. The asteroid's present surface is expected to consist of widespread volcanic terrain, modified extensively by impacts that exposed the underlying crust or possibly the mantle. Hemispheric heterogeneity has been observed by poorly resolved imaging of the surface that suggests the possibility of a physiographic dichotomy as occurs on other terrestrial planets. Vesta might have had an early magma ocean but details of the early thermal structure are far from clear owing to model uncertainties and paradoxical observations from the HEDs. Petrological analysis of the eucrites coupled with thermal evolution modeling recognizes two possible mechanisms of silicate-metal differentiation leading to the formation of the basaltic M.T. Zuber et al.achondrites: equilibrium partial melting or crystallization of residual liquid from the cooling magma ocean. A firmer understanding the plethora of complex physical and chemical processes that contribute to melting and crystallization will ultimately be required to distinguish among these possibilities. The most prominent physiographic feature on Vesta is the massive south polar basin, whose formation likely re-oriented the body axis of the asteroid's rotation. The large impact represents the likely major mechanism of ejection of fragments that became the HEDs. Observations from the Dawn mission hold the promise of revolutionizing our understanding of 4 Vesta, and by extension, the nature of collisional, melting and differentiation processes in the nascent solar system. Large Asteroids as Planetary EmbryosThe largest asteroids are central to understanding nascent planetary evolution, and among these 4 Vesta plays a unique role in the reconstruction of the physical and chemical processes that comprise collectively terrestrial planet accretion. Vesta is alone among the largest asteroids in having a basaltic crust (McCord et al. 1970) indicative of silicate volcanic and/or plutonic processes (Binzel et al. 2003). Observations of surface spectra (McCord et al. 1970;Binzel and Xu 1993) in concert with information on ...

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