The behaviour of pebbles around the snowline in protoplanetary disks Djoeke Schoonenberg University of Amsterdam with Chris Ormel, Beibei Liu, Sebastiaan Krijt SPF2, Biosphere, 15 March 2018 Image: A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO) Water snowline around V883 Ori Cieza et al., Nature, 535, 2016 Schoonenberg, Okuzumi, & Ormel, A&A, 605, L2 (2017) Outline • Planetesimal formation by streaming instability around the snowline • Formation of the TRAPPIST-1 planets From dust to planets planet planetesimal dust µm km 1e3 km Not to scale! (not even to log-scale) Streaming instability • Mechanism to directly form planetesimals from pebbles • Requires local solids-to-gas ratio of order unity Johansen, Youdin, & Mac Low 2009 (see also Youdin & Goodman 2005; Johansen, Henning, & Klahr 2006; Krijt et al. 2016 Johansen & Youdin 2007; (see also Birnstiel et al. 2012, Simon et al. 2016; Yang et al. 2017) Lambrechts & Johansen 2014) Planetesimal formation outside the snowline: a local transport model snowline constant mass flux of icy pebbles Schoonenberg & Ormel, A&A, 602, A21 (2017) e-folding timescale ≈ (rpeak - rsnow) / vgas 3 ˙ 8 1 ↵ =3 10− Mgas = 10− M yr− · 2 ˙ ˙ ⌧ =3 10− Mpeb/Mgas =0.8 Schoonenberg & Ormel, A&A, 602, A21 (2017) · Icy pebble designs ‘single-seed’ evaporation front ‘many-seeds’ Icy pebble designs ‘single-seed’ evaporation front ‘many-seeds’ Michael Hammer, Astrobites Many-seeds model enhances ‘bump’ and leads to planetesimal ice fraction of ~0.5 Schoonenberg & Ormel, A&A, 602, A21 (2017) ‘free silicates’ ‘dirt’ 3 ˙ 8 1 ↵ =3 10− Mgas = 10− M yr− · 2 ˙ ˙ ⌧ =3 10− Mpeb/Mgas =0.8 · Formation scenario for the TRAPPIST-1 planets Ormel, Liu, and Schoonenberg, A&A, 604, A1 (2017) Grimm et al., A&A, in press Jack Cook/WHOI/USGS Water fraction of TRAPPIST-1 planets dictated by ratio of icy pebble accretion to water-poor pebble accretion Ormel, Liu, and Schoonenberg, A&A, 604, A1 (2017) planetesimal formation + pebble accretion (no migration / planetesimal mergers) Planetesimal mergers and migration Using MERCURY (Chambers 1999) g16 Planetesimal mergers and migration Using MERCURY (Chambers 1999) g17 Planetesimal mergers and migration first planetary embryo has crossed snowline Using MERCURY (Chambers 1999) g18 b c d e f g h 3 ↵ = 10− 10 1 M˙ gas = 10− M yr− Z =0.02 Take home messages • Planetesimal formation in our TRAPPIST-1 model starts after a few 10^3 years • First planet embryo migrates across the snowline after a few 10^4 years • Without migration, planetesimal formation is a self-limiting process (because pebble flux goes down due to pebble accretion as planetesimal mass grows) • Icy pebble accretion versus rocky pebble accretion after iceline-crossing determines bulk composition of TRAPPIST-1 planets • PRELIMINARY: water fractions of a few percent seem to be feasible.