Formation of Planetesimals: The Building Blocks of Planets
Planetesimals are traditionally defined as solid objects (rocky or icy or a combination of both) whose internal strength is dominated by self-gravity rather than material strength. This corresponds to bodies of approximately 100 m to 1 km in size (Benz 2000). However, this definition does not take into account the role of the body in the planet-building process. Planetesimals of km in size are vulnerable to erosion and fragmentation in collisions with other planetesimals at the speeds relevant in protoplanetary disks (Ida et al. 2008). One can instead define the planetesimal formation stage as the growth of bodies to sufficient sizes to be insensitive to disruption in collisions with equal-sized bodies. This stage of planet formation may extend to as large as 1,000 km in size, depending on the strength of the gas turbulence which is responsible for inducing high planetesimal-planetesimal speeds.
Planet formation takes place in protoplanetary disks of gas and dust...