Collisional processes in extrasolar planetesimal discs – dust clumps in Fomalhaut's debris disc
By M. C. Wyatt, W. R. F. Dent. 2002
211 citations recorded by the source corpus.
This paper presents a model for the outcome of collisions between planetesimals in a debris disc, and assesses the impact of collisional processes on the structure and size distribution of the disc. The model is presented by its application to Fomalhaut’s collisionally replenished dust disc; a recent 450-µm image of this disc shows a clump embedded within it with a flux ∼5 per cent of the total. The following conclusions are drawn. (i) Spectral energy distribution modelling is consistent with Fomalhaut’s disc having a collisional cascade size distribution extending from bodies 0.2 m in diameter (the largest that contribute to the 850-µm flux) down to 7-µm-sized dust (smaller grains are blown out of the system by radiation pressure). (ii) Collisional lifetime arguments imply that the collisional cascade starts with planetesimals 1.5‐4 km in diameter, and so has a mass of 20‐30 M⊕. Any larger bodies must be predominantly primordial. (iii) Constraints on the time-scale for the ignition of the collisional cascade from planet formation models are consistent with these primordial planetesimals having the same distribution as the cascade extending up to 1000 km, resulting in a disc mass of 5‐10 times the minimum solar nebula mass. (iv) The debris disc is expected to be intrinsically clumpy, as planetesimal collisions result in dust clumps that can last up to 700 orbital periods. The intrinsic clumpiness of Fomalhaut’s disc is below current detection limits, but it could be detectable by future observatories such as ALMA, and could provide the only way of determining this primordial planetesimal population. Also, we note that such intrinsic clumpiness in an exozodiacal cloudlike disc could present a confusion limit when trying to detect terrestrial planets. (v) The observed clump could have originated in a collision between two runaway planetesimals, both larger than 1400 km in diameter. It appears unlikely that we should witness such an event unless both the formation of these runaways and the ignition of the collisional cascade occurred relatively recently (within the last ∼10 Myr), however this is a topic which would benefit from further exploration using planet formation and collisional models. (vi) Another explanation for Fomalhaut’s clump is that ∼5 per cent of the planetesimals in the ring were trapped in 1:2 resonance with a planet orbiting at 80 au when it migrated out as a result of the clearing of a residual planetesimal disc. The motion on the sky of such a clump would be 0.2 arcsec yr −1 ,
Subfields: Astronomy and Astrophysics
View Paper: https://www.semanticscholar.org/paper/2e16277ecf5a1b5ee27ca404fd83b228f883e148
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In Astronomy and Astrophysics
Citations in the corpus
- Collisional processes and size distribution in spatially extended debris discs (2007, result): “For the large–scale regime just below the fragmentation threshold, we follow Wyatt & Dent (2002) and assume: Mcra = 0.5Mt ( Qimp Q∗ ) if 0.2Q∗ < Qimp < Q ∗ (B.6) which is in agreement with the experiment results displayedin Fig.5 of Housen et al. (1991).”
- The Insignificance of P-R drag in detectable extrasolar planetesimal belts (2005, background): “In reality the collisional lifetime depends on particle size, in a way which depends on the size distribution of dust in the disk, and the size of impactor required to destroy the particle, rather than result in a non-destructive collision (e.g., Wyatt & Dent 2002).”
- Predictions for a planet just inside Fomalhaut's eccentric ring (2006, background): “The low scaleheight implied by the sharp edge suggests that fewer collisions are destructive than previously estimated (e.g. by Wyatt & Dent 2002).”
- Planet Hunters IX. KIC 8462852-where's the flux? (2015, background): “One possibility is that the dimming events are caused by dust thrown off in collisions between planetesimals in an otherwise unseen asteroid belt analogue (e.g. Wyatt & Dent 2002; Zeegers, Kenworthy & Kalas 2014).”
- Frequency of Debris Disks around Solar-Type Stars: First Results from a Spitzer MIPS Survey (2005, background): “Note that for the sub-mm flux, it is no longer appropriate to assume blackbody emission; as the wavelength of the emitted radiation becomes long compared to 2πagrain, the effective grain absorption cross-section begins to fall off as λ−1 to λ−2 (Draine & Lee 1984; Wyatt & Dent 2002).”
- Collisional Cascades in Planetesimal Disks. II. Embedded Planets (2003, background): “The nearby A-type star Fomalhaut also has a distinct clump in its debris disk (Wyatt & Dent 2002; Holland et al. 2003).”
- Variations on Debris Disks: Icy Planet Formation at 30-150 AU for 1-3 M☉ Main-Sequence Stars (2008, background): “Catastrophic collisions may also produce diversity among A star debris disks (e.g., Wyatt & Dent 2002; Su et al. 2005).”
- Steady State Evolution of Debris Disks around A Stars (2007, background): “D, defined as the specific incident energy required to catastrophically destroy a particle such that (Wyatt & Dent 2002): Xc = 1.3× 10−3 [ Q?”
- Resonant Trapping of Planetesimals by Planet Migration: Debris Disk Clumps and Vega’s Similarity to the Solar System (2003, background): “…showed that some grain growth must have occurred in these systems, since this dust is short-lived and so must be continually replenished (e.g., Backman & Paresce 1993); the dust is thought to originate in a collisional cascade that starts with planetesimals a few km in size (Wyatt & Dent 2002).”
- Dust distributions in debris disks: effects of gravity, radiation pressure and collisions (2006, background): “…found in most of the debris disks and attributed to the gravity of presumed planets (Wyatt et al. 1999; Ozernoy et al. 2000; Moro-Martín & Malhotra 2002; Quillen & Thorndike 2002; Wyatt & Dent 2002; Wilner et al. 2002; Kuchner & Holman 2003; Moran et al. 2004; Deller & Maddison 2005, among others).”
- COLLISIONS BETWEEN GRAVITY-DOMINATED BODIES. I. OUTCOME REGIMES AND SCALING LAWS (2011, methodology): “Using the method from Wyatt & Dent (2002) and Paardekooper, Leinhardt, and Thebault (in preparation), the mass of the second largest remnant, Mslr, is fully constrained by knowledge of the mass/size of the largest remnant and the power-law slope for the size distribution of the smaller fragments.”
- Transience of Hot Dust around Sun-like Stars (2006, unknown): “The collisional cascade scenario is supported by modeling of the emission spectrum of the dust which shows a size distribution similar to that expected for dust coming from a collisional cascade (Wyatt & Dent 2002, hereafter WD02).”