31 research outputs found
Dynamics of charged dust particles in protoplanetary discs
We study the effect of an imposed magnetic field on the motion of charged
dust particles in magnetically active regions of a protoplanetary disc.
Assuming a power law structure for the vertical and the toroidal components of
the magnetic field for the regions beyond magnetically dead region of the disc,
the radial and the vertical velocities of the charged particles, in the
asymptotic case of small particles, are calculated analytically. While grains
with radii smaller than a critical radius significantly are affected by the
magnetic force, motion of the particles with larger radii is independent of the
magnetic field. The critical radius depends on the magnetic geometry and the
charge of the grains. Assuming that a grain particle has one elementary charge
and the physical properties of the disc correspond to a minimum-mass solar
nebula, we show that only micron-sized grains are affected by the magnetic
force. Also, charge polarity determines direction of the radial velocity. For
such small particles, both the radial and the vertical velocities increase due
to the magnetic force.Comment: Accepted for publication in Astrophysics & Space Scienc
On the origin and evolution of the material in 67P/Churyumov-Gerasimenko
International audiencePrimitive objects like comets hold important information on the material that formed our solar system. Several comets have been visited by spacecraft and many more have been observed through Earth- and space-based telescopes. Still our understanding remains limited. Molecular abundances in comets have been shown to be similar to interstellar ices and thus indicate that common processes and conditions were involved in their formation. The samples returned by the Stardust mission to comet Wild 2 showed that the bulk refractory material was processed by high temperatures in the vicinity of the early sun. The recent Rosetta mission acquired a wealth of new data on the composition of comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G) and complemented earlier observations of other comets. The isotopic, elemental, and molecular abundances of the volatile, semi-volatile, and refractory phases brought many new insights into the origin and processing of the incorporated material. The emerging picture after Rosetta is that at least part of the volatile material was formed before the solar system and that cometary nuclei agglomerated over a wide range of heliocentric distances, different from where they are found today. Deviations from bulk solar system abundances indicate that the material was not fully homogenized at the location of comet formation, despite the radial mixing implied by the Stardust results. Post-formation evolution of the material might play an important role, which further complicates the picture. This paper discusses these major findings of the Rosetta mission with respect to the origin of the material and puts them in the context of what we know from other comets and solar system objects
Giant Planet Formation and Migration
© 2018, The Author(s). Planets form in circumstellar discs around young stars. Starting with sub-micron sized dust particles, giant planet formation is all about growing 14 orders of magnitude in size. It has become increasingly clear over the past decades that during all stages of giant planet formation, the building blocks are extremely mobile and can change their semimajor axis by substantial amounts. In this chapter, we aim to give a basic overview of the physical processes thought to govern giant planet formation and migration, and to highlight possible links to water delivery.S.-J. Paardekooper is supported by a Royal Society University Research Fellowship. A. Johansen is supported by the Knut and Alice Wallenberg Foundation, the Swedish Research Council (grant 2014-5775) and the European Research Council (ERC Starting Grant 278675-PEBBLE2PLANET)