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Wetherill, G. W.; Inaba, Satoshi

doi:10.1023/a:1005211732138

Cited by 16 publications

(5 citation statements)

References 15 publications

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“…Planets form in protoplanetary disks by accretion of kilometer sized protoplanetary bodies, commonly called planetesimals. This later growth phase is driven by gravity (Wetherill & Inaba 2000;Wetherill & Stewart 1993). The planetesimals themselves grow from dust particles, but due to the small size and mass, self gravity is not important during individual collisions and the basic formation process -if a single one can be named -is not yet understood entirely.…”

Section: Introductionmentioning

confidence: 99%

Colliding Decimeter Dust

Deckers

Teiser

2013

ApJ

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Collisional evolution is a key process in planetesimal formation and decimeter bodies play a key role in the different models. However, the outcome of collisions between two dusty decimeter bodies has never been studied experimentally. Therefore, we carried out microgravity collision experiments in the Bremen drop tower. The agglomerates consist of quartz with irregularly shaped micrometer-sized grains and the mean volume filling factor is 0.437 ± 0.004. The aggregates are cylindrical with 12 cm in height and 12 cm in diameter, and typical masses are 1.5 kg. These are the largest and most massive dust aggregates studied in collisions to date. We observed rebound and fragmentation but no sticking in the velocity range between 0.8 and 25.7 cm s −1 . The critical fragmentation velocity for split up of an aggregate is 16.2 ± 0.4 cm s −1 . At lower velocities the aggregates bounce off each other. In this velocity range, the coefficient of restitution decreases with increasing collision velocity from 0.8 to 0.3. While the aggregates are very weak, the critical specific kinetic energy for fragmentation Q μ=1 is a factor of six larger than expected. Collisions of large bodies in protoplanetary disks are supposed to be much faster and the generation of smaller fragments is likely. In planetary rings, collision velocities are of the order of a few cm s −1 and are thereby in the same range investigated in these experiments. The coefficient of restitution of dust agglomerates and regolith-covered ice particles, which are common in planetary rings, are similar.

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Section: Introductionmentioning

confidence: 99%

Colliding Decimeter Dust

Deckers

Teiser

2013

ApJ

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“…Nevertheless, there are several noteworthy exceptions. Wetherill & Inaba (2000) considered that planetesimals progressively appear over a 10 5 years timescale, but only considered mutual planetesimal accretion as a possible growth mode, implicitly neglecting the contribution of dust. Morbidelli et al (2009), while attempting to fit the known asteroidal size-distribution, did consider in one of their simulations the possible accretion of dust by planetesimals which formed early, but did so only for one specific case: large, 100 km sized seed-planetesimals produced over 2 Myr.…”

Section: Introductionmentioning

confidence: 99%

From Dust to Planetesimal: The Snowball Phase?

Xie¹,

Payne²,

Thébault³

et al. 2010

ApJ

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The standard model of planet formation considers an initial phase in which planetesimals form from a dust disk, followed by a phase of mutual planetesimal-planetesimal collisions, leading eventually to the formation of planetary embryos. However, there is a potential transition phase (which we call the "snowball phase"), between the formation of the first planetesimals and the onset of mutual collisions amongst them, which has often been either ignored or underestimated in previous studies. In this snowball phase, isolated planetesimals move on Keplerian orbits and grow solely via the direct accretion of sub-cm sized dust entrained with the gas in the protoplanetary disk. Using a simplified model in which planetesimals are progressively produced from the dust, we consider the expected sizes to which the planetesimals can grow before mutual collisions commence and derive the dependence of this size on a number of critical parameters, including the degree of disk turbulence, the planetesimal size at birth and the rate of planetesimal creation. For systems in which turbulence is weak and the planetesimals are created at a low rate and with relatively small birth size, we show that the snowball growth phase can be very important, allowing planetesimals to grow by a factor of 10 6 in mass before mutual collisions take over. In such cases, the snowball growth phase can be the dominant mode to transfer mass from the dust to planetesimals. Moreover, such growth can take place within the typical lifetime of a protoplanetary gas disk. A noteworthy result is that, for a wide range of physically reasonable parameters, mutual collisions between planetesimals become significant when they reach sizes ∼ 100 km, irrespective of their birth size. This could provide an alternative explanation for the turnover point in the size distribution of the present day asteroid belt. For the specific case of close binaries such as α Centauri, the role of snowball growth could be even more important. Indeed, it provides a safe way for bodies to grow through the problematic ∼1 to 50 km size range for which the perturbed environment of the binary can prevent mutual accretion of planetesimals. From a more general perspective, these preliminary results suggest that an efficient snowball growth phase provides a large amount of "room at the bottom" for theories of planet formation.

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“…5 5 In this case, the very concept of an ‘initial’ planetesimal population might be questioned (see e.g. Wetherill & Inaba 2000). …”

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confidence: 99%

Planet formation in α Centauri A revisited: not so accretion friendly after all

Thébault

Marzari

Scholl

2008

Monthly Notices of the Royal Astronomical Society

102

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We numerically explore planet formation around α Centauri A by focusing on the crucial planetesimals-to-embryos phase. Our approach is significantly improved with respect to the earlier work of Marzari & Scholl, since our deterministic N-body code computing the relative velocities between test planetesimals handles bodies with different size. Due to this step-up, we can derive the accretion versus fragmentation trend of a planetesimal population having any given size distribution. This is a critical aspect of planet formation in binaries since the pericenter alignment of planetesimal orbits due to the gravitational perturbations of the companion star and to gas friction strongly depends on size. Contrary to Marzari & Scholl, we find that, for the nominal case of a Minimum-Mass Solar Nebula gas disc, the region beyond ~0.5au from the primary is strongly hostile to planetesimal accretion. In this area, impact velocities between different-sized bodies are increased, by the differential orbital phasing, to values too high to allow mutual accretion. For any realistic size distribution for the planetesimal population, this accretion-inhibiting effect is the dominant collision outcome and the accretion process is halted. Results are relatively robust with respect to the profile and density of the gas disc. Except for an unrealistic almost gas-free case, the inner `accretion-safe' area never extends beyond 0.75au. We conclude that planet formation is very difficult in the terrestrial region around α Centauri A, unless it started from fast-formed very large (>30km) planetesimals. Notwithstanding these unlikely initial conditions, the only possible explanation for the presence of planets around 1au from the star would be the hypothetical outward migration of planets formed closer to the star or a different orbital configuration in the binary's early history. Our conclusions differ from those of several studies focusing on the later embryos-to-planets stage, confirming that the planetesimals-to-embryos phase is more affected by binary perturbations

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Cited by 16 publications

References 15 publications

Colliding Decimeter Dust

Colliding Decimeter Dust

From Dust to Planetesimal: The Snowball Phase?

Planet formation in α Centauri A revisited: not so accretion friendly after all

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