{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"681c74b65c9d08d3243ff393d35623d0577aad426b7bb088f49a3070d353a061","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"2122435e26721b49f348134d93b345823a3ab6c7d16b36af28cf70582dd13fb0","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":[],"external_id":"astro.planetesimal-formation.meter-barrier","kind":"phenomenon","literature_status":"open","n":"1","parents":[],"plain":"Pebbles and boulders feel a headwind from the gas disk, so they lose orbital speed and spiral into the star in a few hundred orbits, and they shatter when they collide. Some process must form kilometer bodies faster than this.","posed_since":"1977","precise":"Particles with Stokes number $\\mathrm{St} = \\Omega t_{\\mathrm{stop}} \\sim 0.1-1$ drift inward at $v_{r} \\sim 2\\,\\mathrm{St}\\,\\eta\\,v_{K}/(1+\\mathrm{St}^{2})$ with $\\eta v_{K} \\sim 3-5x10^{3}\\,\\mathrm{cm/s}$ and collide at speeds above fragmentation thresholds of $\\sim 10^{2}-10^{3}\\,\\mathrm{cm/s}$. Identify which pathway forms bound planetesimals of $1-100\\,\\mathrm{km}$ fast enough: streaming instability, trapping in pressure bumps or vortices, gravitational instability of the dust layer, or coagulation of porous ice aggregates.","problem_ref":null,"references":"","settled_by":"Disk models that form planetesimals in measured disk conditions and reproduce the size distribution and binarity of primordial Kuiper-belt objects.","status_note":"","title":"How do solids grow past the drift and fragmentation barriers?","topic_ref":"31e036d86c734de67f0897bf2bb6f507ef858098857fb27d31ab4bb1d62da4e6"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"575381764f0952e6e35971a61db7d04d95345419df4465f7e11d2e986e927dab","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"ffe0bd735710c5eb7dad4838f9bd3fe70c77536e7a6fe8ba1cc08afeb24b226f","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"IrQVg_Vz45Agtyp-dcy4Wqi8Ye9XikJVWZdJpIJmgbV4iOUWXwyWcfkNeB9F943MTd62X_CJEQAHwTmn5_x5Ag"},"schema":"pubphys.envelope/1"},"record_hash":"575381764f0952e6e35971a61db7d04d95345419df4465f7e11d2e986e927dab","leaf_index":575}