IDA , Shigeru

Context. Forming planetesimals from pebbles is a major challenge in our current understanding of planet formation. In a protoplanetary disk, pebbles drift inward near the disk midplane via gas drag and they may enter a zone of reduced turbulence (dead zone). In this context, we identified that the backreaction of the drag of pebbles onto the...

Context. Circumstellar disks are known to contain a significant mass in dust ranging from micron to centimeter size. Meteorites are evidence that individual grains of those sizes were collected and assembled into planetesimals in the young solar system. Aims. We assess the efficiency of dust collection of a swarm of non-drifting planetesimals...

Context. A notable challenge of planet formation is to find a path to directly form planetesimals from small particles. Aims. We aim to understand how drifting pebbles pile up in a protoplanetary disk with a nonuniform turbulence structure. Methods. We consider a disk structure in which the midplane turbulence viscosity increases with the...

Context. The formation of rocky planetesimals is a long-standing problem in planet formation theory. One of the possibilities is that it results from gravitational instability as a result of the pile-up of small silicate dust particles released from sublimating icy pebbles that pass the snow line. Aims. We want to understand and quantify the...

The high density of the recently discovered close-in extrasolar planet HD 149026b suggests the presence of a huge core in its interior, which challenges planet formation theory. We first derive constraints on the total mass of heavy elements in the planet and find its preferred value is 50-80 M? . We then explore the possibility of the...

Context. Forming planetesimals is a major challenge in our current understanding of planet formation. Around the snow line, icy pebbles and silicate dust may locally pile up and form icy and rocky planetesimals via a streaming instability and/or gravitational instability. The scale heights of both pebbles and silicate dust released from...

Context. The formation of rocky planetesimals is a long-standing problem in planet formation theory. One of the possibilities is that it results from gravitational instability as a result of the pile-up of small silicate dust particles released from sublimating icy pebbles that pass the snow line. Aims. We want to understand and quantify the...

We present the first measurements of Jupiter's wind profile obtained from radial-velocity measurements. Radial velocity measurements of wind are rather difficult, but can be very interesting as they measure the actual speed of cloud particles instead of the motion of large cloud structures. Here we present the first scientific results of the...

We present the first measurements of Jupiter's wind profile ever obtained with Doppler velocity measurements in the visible. Hitherto, knowledge about atmospheric dynamics has been obtained with cloud-tracking techniques , which consist of tracking visible features from images taken at different dates. However, cloud tracking indicates the...

Uranus and Neptune are the archetypes of "ice giants", a class of planets that may be among the most common in the Galaxy. They hold the keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres inside and outside the solar system; however, they are also the last unexplored planets of the Solar System. ...