Georgi Paraskov - Academia.edu (original) (raw)
Uploads
Papers by Georgi Paraskov
Planetesimals and their precursors in protoplanetary disks are very porous. Thus, a gas flow arou... more Planetesimals and their precursors in protoplanetary disks are very porous. Thus, a gas flow around such bodies will be accompanied by gas flow through them. We calculate how this gas flow will influence the impact of a small body on a body larger than 1 m in size. On the front side of a large body (target) with high porosity there is a boundary layer that is characterized by a gas flow toward the surface. We find that under typical conditions with respect to collisions in protoplanetary disks, fragments of a collision will stay inside this boundary layer. These fragments will return to the target by gas drag. Net growth of the larger body in these secondary collisions will occur. The mechanism works for all sizes up to planetesimal size. This supports the idea that planetesimals (kilometer-sized bodies) build up from collisions of smaller bodies. Subject headings: hydrodynamics — planetary systems: protoplanetary disks — planets and satellites: formation — solar system: formation 1.
Summary We discuss the possibility of erosion of dusty bodies in protoplanetary disks by a subson... more Summary We discuss the possibility of erosion of dusty bodies in protoplanetary disks by a subsonic laminar gas flow. Our analysis is based on wind tunnel experiments on cm-size dust targets in an air gas flow of 63m/s at static gas pressures between 0.1mbar and 4.5mbar. We compare the results to numerical calculations of gas flow through porous bodies and the resulting drag force on dust aggregates at the surface. Our studies imply that a dusty body is efficiently eroded if the dynamic gas pressure of the surface flow exceeds gravity and/or cohesion. Applied to protoplanetary disks we find that objects on circular orbits might be relatively safe against erosion in a laminar gas flow even in a dense disk. However, if a body is stirred up to eccentric orbits its relative motion to the gas increases. Such objects can significantly be eroded if they consist of dust. As an extreme a 100m body with the rather low eccentricity of an Earth orbit might be eroded in a single orbit. The effec...
We discuss the problem of planet formation and give an account of the standard model. Our aim is ... more We discuss the problem of planet formation and give an account of the standard model. Our aim is to investigate some missing links in this model. In impact experiments we study central collisions between mm-sized dust projectiles and cm-sized dust targets. Collision velocities range from 6 to 38 m/s. The general outcome of a collision strongly depends on the target type. We prepared highly porous targets (porosity between 74% and 84%) and compressed targets with porosity of 68%. Impacts into porous targets result in craters, which are several mm deep and 2-3 cm in diameter. We observe ejecta that originate not from the crater but from the whole target surface. Responsible for particle ejection are elastic waves induced by the impact. Most of the mass of the projectile is added to the target mass due to gravity but mass loss of the target would result under microgravity. Impacts into compressed targets result in a pyramid like dust structure on top of the original target surface. At ...
In experiments and calculations we find that net growth of a body in a binary collision at `high ... more In experiments and calculations we find that net growth of a body in a binary collision at `high speed' (several tens of m/s) is possible if the colliding bodies both consist of dust and gas flow (in protoplanetary disks) is taken into account.
Protostars and Planets V Posters, 2005
Planetesimals and their precursors in protoplanetary disks are very porous. Thus, a gas flow arou... more Planetesimals and their precursors in protoplanetary disks are very porous. Thus, a gas flow around such bodies will be accompanied by gas flow through them. We calculate how this gas flow will influence the impact of a small body on a body larger than 1 m in size. On the front side of a large body (target) with high porosity there is a boundary layer that is characterized by a gas flow toward the surface. We find that under typical conditions with respect to collisions in protoplanetary disks, fragments of a collision will stay inside this boundary layer. These fragments will return to the target by gas drag. Net growth of the larger body in these secondary collisions will occur. The mechanism works for all sizes up to planetesimal size. This supports the idea that planetesimals (kilometer-sized bodies) build up from collisions of smaller bodies. Subject headings: hydrodynamics — planetary systems: protoplanetary disks — planets and satellites: formation — solar system: formation 1.
Summary We discuss the possibility of erosion of dusty bodies in protoplanetary disks by a subson... more Summary We discuss the possibility of erosion of dusty bodies in protoplanetary disks by a subsonic laminar gas flow. Our analysis is based on wind tunnel experiments on cm-size dust targets in an air gas flow of 63m/s at static gas pressures between 0.1mbar and 4.5mbar. We compare the results to numerical calculations of gas flow through porous bodies and the resulting drag force on dust aggregates at the surface. Our studies imply that a dusty body is efficiently eroded if the dynamic gas pressure of the surface flow exceeds gravity and/or cohesion. Applied to protoplanetary disks we find that objects on circular orbits might be relatively safe against erosion in a laminar gas flow even in a dense disk. However, if a body is stirred up to eccentric orbits its relative motion to the gas increases. Such objects can significantly be eroded if they consist of dust. As an extreme a 100m body with the rather low eccentricity of an Earth orbit might be eroded in a single orbit. The effec...
We discuss the problem of planet formation and give an account of the standard model. Our aim is ... more We discuss the problem of planet formation and give an account of the standard model. Our aim is to investigate some missing links in this model. In impact experiments we study central collisions between mm-sized dust projectiles and cm-sized dust targets. Collision velocities range from 6 to 38 m/s. The general outcome of a collision strongly depends on the target type. We prepared highly porous targets (porosity between 74% and 84%) and compressed targets with porosity of 68%. Impacts into porous targets result in craters, which are several mm deep and 2-3 cm in diameter. We observe ejecta that originate not from the crater but from the whole target surface. Responsible for particle ejection are elastic waves induced by the impact. Most of the mass of the projectile is added to the target mass due to gravity but mass loss of the target would result under microgravity. Impacts into compressed targets result in a pyramid like dust structure on top of the original target surface. At ...
In experiments and calculations we find that net growth of a body in a binary collision at `high ... more In experiments and calculations we find that net growth of a body in a binary collision at `high speed' (several tens of m/s) is possible if the colliding bodies both consist of dust and gas flow (in protoplanetary disks) is taken into account.
Protostars and Planets V Posters, 2005