Correct Option
The correct option is Second stage.
Explanation
The standard model of planet formation, primarily based on the Nebular Hypothesis, describes the evolution of the solar system from a rotating cloud of gas and dust. This process is generally divided into three distinct stages, leading from a nebula to fully formed planets.
Analysis of Stages
- First Stage: The process begins with a localized lump of gas within a nebula. Gravitational forces cause the core to collapse, forming a protostar, while a huge rotating disc of gas and dust develops around it.
- Second Stage (Correct): The gas cloud condenses, and matter around the core aggregates into small, rounded objects. Through the process of cohesion, these objects develop into planetesimals. This stage is characterized by the formation of a large number of smaller solid bodies through collision and gravitational attraction.
- Third Stage: The numerous planetesimals collide and accrete (stick together) to form fewer, larger bodies, eventually resulting in the formation of planets.
Key Takeaway
Planetesimals are intermediate solid bodies formed during the second stage of planet formation through the condensation of the solar nebula and the cohesion of dust particles.