Ablation of Boulder-Sized Objects Dust, Pebbles and Minor Bodies - PowerPoint PPT Presentation

Radial Drift and Concurrent Ablation of Boulder-Sized Objects Dust, Pebbles and Minor Bodies 2019 – NCCR PlanetS Workshop Bern Remo Burn , Ulysse Marboeuf, Yann Alibert & Willy Benz Physikalisches Institut, Universität Bern, Sidlerstrasse 5, 3012 Bern, Switzerland remo.burn@space.unibe.ch

Introduction 2/24

Introduction  Icy bodies crossing the snowline due to radial drift  Caused by gas drag  Quantify efficiency of water transport  Focus on H 2 O ice line (i.e. the snowline) 3/24

Boulder size range  Pebbles and Cobbles sublimate fast and drift slow (e.g. Schoonenberg, Ormel 2017, Drazkowska 2017)  Boulders with r ≳ 1m drift fast and take longer to lose ice  Planetesimals (r ≳ 200m) drift slower than snowline  They never cross it by gas induced drift 4/24

Methods 5/24

Cometary Nucleus Model  Model from Marboeuf 2008, Marboeuf et al., 2012  1-D mode used  Heat, gas and dust grain transport  Sublimation/Condensation of volatiles  Dust mantle formation / removal possible Coma Surface T Gas + grains Cometary Disk Model Nucleus Model R, ρ silicates H 2 O H 2 O 6/24

Radial Drift − 2𝑏𝜃Ω Quadratic Regime 𝑒𝑏 𝑡 𝑒𝑢 = 𝑡 2 − 2𝑏𝜃Ω Epstein or Stokes (laminar) Regime 1 + 𝑡 2 𝑡 𝜍 𝑡 𝑆Ω 2𝑆 6𝑤 𝑢ℎ𝑓𝑠𝑛  Stokes Number 𝑡 = 𝑢 𝑡 Ω = × 1, 3𝜇 , 𝜍 𝑕 𝑤 𝑢ℎ𝑓𝑠𝑛 Δ𝑤 7/24

Results (BURN ET AL. SUBMITTED TO A&A) 8/24

Single Boulder 9/24

Sublimation Model 10/24

Size Dependence 11/24

Size Dependence 12/24

Size Dependence 13/24

Size Dependence  Assume a size distribution 𝑜 𝑛 𝑒𝑛 = ቊ𝐵𝑛 𝛽 for 𝑛 ∈ [𝑑 𝑚 , 𝑑 𝑣 ] 𝑒𝑛 0 else  𝑑 𝑚 = 1 kg 𝑑 𝑣 = 1 × 10 9 kg  Integral over all included masses  Mean in time evolution of the disk 14/24

Dust Mantle 15/24

Different Disks 16/24

Applicability 17/24

Collisions 18/24

Collision Rate «Stokes» collision rate (Safronov 1969)  2 𝑑𝑝𝑚 = 𝑜 𝑊 𝑛 𝑗 𝜌 𝑆 𝑢 + 𝑆 𝑗 2 Δ𝑤 1 + 𝑤 𝑓𝑡𝑑 Γ Δ𝑤 2 𝑛 𝑢 +𝑛 𝑗 2 𝑤 𝑓𝑡𝑑 = 2𝐻  𝑆 𝑢 +𝑆 𝑗 Integrate over all masses of impactors 𝑛 𝑗  Dust and larger particles settle to the midplane  Balanced by turbulence  𝛽 Scale height is suppressed ℎ 𝑡 = ℎ 𝑕 𝛽+𝑡 (Youdin&Lithwick 2007,Fromang&Nelson  2009, Birnstiel 2016) Stop settling at 1% of gas scale height  𝜃𝑤 𝑙 Relative velocity Δ𝑤 depends on radial and azimuthal contributions  1+𝑡 2 Neglected contributions: Settling speed, Turbulence, Brownian Motion  19/24

Collision Rates Γ 𝑑𝑝𝑚 (Collisions/yr) 𝑛 𝑢 Minimum Impactor Mass (g) 20/24

Erosion  Erosion by collisions with smaller bodies:  Total mass erosion rate for a drifting boulder with 𝑠 = 10 m 2 − 10 × 10 −2 % yr −1  Timescale of modelled process 100 – 1000 yr 21/24

Conclusions 22/24

Conclusion  Boulders > ca. 10 m reach the same distance to the star (pileup)  For self-similar size distribution (-1.83) of drifting bodies, the location of 50% water fraction is shifted by 2%  Water presence limit closer by 15% than the standard one  Independent of time and disk initial conditions  Stable dust mantle has a huge impact on the location  50% closer to the star compared to standard ice line  No sublimation from surface layer, need diffusion through surface layer 23/24

Outlook  Take into account pressure of gas disk in a self-consistent way  Adding H 2 , He to nucleus model  Eccentric or scattered case  Effects for bigger planetesimals  Additional heating process  Heat due to gas drag most significant  Possible to see signature of this process in the future?  Combination with pebble sublimation needed  CO, CO 2 lines  Could small boulders keep their size when sublimating (becoming fluffy)? 24/24