{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"c2f58edc1d29f9f8f008e172223e6e7f213f123ba72bc83ae9f6e02a1ea02a5f","created":"2026-10-03T07:17:55Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011","575381764f0952e6e35971a61db7d04d95345419df4465f7e11d2e986e927dab"],"salt":"1b3f389f57d1227691f6491596dbe9ab68ee97103f53fb035c91f9bf7f766cd7","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"astro.planetesimal-formation.initial-size","kind":"well-posed","literature_status":"open","n":"1","parents":[{"note":"","parent_revision":"575381764f0952e6e35971a61db7d04d95345419df4465f7e11d2e986e927dab","relation":"special_case"}],"plain":"If planetesimals form by sudden gravitational collapse, they should be born big, around 100 kilometers. The size mix at birth determines how fast planets can grow afterwards.","posed_since":"","precise":"Predict and measure $\\mathrm{d}N/\\mathrm{d}D$ of planetesimals at formation. Streaming-instability collapse simulations give a top-heavy distribution peaking near $D \\sim 100\\,\\mathrm{km}$; test against the size distribution and binary fraction of cold classical Kuiper-belt objects and against asteroid-belt constraints. The answer is $\\mathrm{d}N/\\mathrm{d}D$ at birth with its dependence on disk conditions.","problem_ref":null,"references":"","settled_by":"Kuiper-belt surveys complete to $D \\sim 1-10\\,\\mathrm{km}$ plus collapse simulations that resolve fragmentation into binaries and smaller bodies.","status_note":"","title":"What is the birth size distribution of planetesimals?","topic_ref":"31e036d86c734de67f0897bf2bb6f507ef858098857fb27d31ab4bb1d62da4e6"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"af7d1af886865fe1e742dd56f8da8bfe62775ac6d85100ef33f4d91d86af9ddb","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"cd097f404583dd55ea08739eb22aeb9ada15093c2724d79ad440cde1e7a727fa","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"dhI0olQNeY-KP2mNS5zgUaKmR6UUlhLooe_JS8AwW5pQQdV0bLZO8kjzRwCP_lng-aCmZL0tD5GJAQBLwHXuCg"},"schema":"pubphys.envelope/1"},"record_hash":"af7d1af886865fe1e742dd56f8da8bfe62775ac6d85100ef33f4d91d86af9ddb","leaf_index":576}