• CART Astrophysics Seminar Series

April 9, 2026 2:00 PM - April 9, 2026 3:00 PM
PAIS 3205

Host:

Diana Dragomir

Presenter:

Debanjan Sengupta (NMSU)

The formation of planets was shaped by the formation of the first large planetesimals in the protoplanetary nebula. Moreover, the properties of primitive meteorites derived from these planetesimals provide our only ground truth about the nebula. The mechanism through which these ~ 100 km size objects formed is one of the fundamental unsolved questions in the big picture of planet formation. As of now, the most popular mechanism to form these objects is the Streaming Instability (SI) which can produce gravitationally bound over-densities starting in the form of axisymmetric filaments. This mechanism works favorably when the particle sizes are dm-size or larger and the disk is nearly nonturbulent. However, recent theoretical studies, astronomical observations, and meteoritical evidence more strongly support a turbulent solar nebula with particles reaching up to mm-cm size.

In this talk, I shall present a new and novel pathway to the formation of planetesimals, also known as Turbulent Concentration (TC). It has been known since the early 90's that particles are preferentially concentrated in turbulence to different degrees across flow scales, in a size-dependent way and sometimes by very large factors. However, the studies pertaining to this mechanism in the context of planetesimal formation have been only statistical in nature. Here, we present our results from the first 3D high resolution TC simulations under protoplanetary disk conditions including rotation, radial shear, and vertical gravity. These results are compared with prior statistical predictions and will eventually be used to predict the rate of planetesimal formation by TC. Finally, we for the first time, demonstrate the formation of planetesimals in a globally turbulent condition from small particles with abundance a few times the solar value.