Suppose that a planetary system is now forming around some protostar in the sky. In what ways might this planetary system turn out to be similar to or different from our own solar system? Explain your reasoning.

Imagine a vast, gently swirling whirlpool of gas and dust rotating around a young star; this is the birthplace of planets, known as the protoplanetary disk. This disk forms during the early stages of star formation, as the gravitational collapse of a molecular cloud causes the cloud to spin and flatten out into a disk shape. Within this disk, the conditions are ripe for the creation of new worlds.

Dust particles within the disk start to collide and stick together, gradually building up larger and larger clumps. Over time, these clumps can become kilometer-sized bodies, setting the stage for further growth into fully-fledged planets. The composition of this disk is a mix of ices, silicates, and metallics, varying in density and temperature, which means the type of planets formed can vary widely. Since no two disks are alike, this explains the immense variety in planetary systems observed by astronomers.

The building blocks of planets are called planetesimals, and they play a pivotal role in planetary system formation. These are solid objects, thought to be formed through a process known as 'accretion', where dust particles in the protoplanetary disk stick together upon collisions, forming ever-larger bodies.

Dawn of the Planetesimals

Planetesimals represent a significant step in planetary evolution, being the intermediate stage between dust grains and fully-formed planets. Once they reach a certain size, typically 1 kilometer or more in diameter, they exert enough gravitational pull to attract additional matter, growing increasingly massive. This stage can lead to a runaway accretion process, where the growth rate accelerates dramatically and leads to the eventual birth of planets.

The term celestial bodies encompasses a wide array of objects in space, including planets, moons, asteroids, comets, and stars. Each celestial body has its own unique characteristics, determined by its formation, composition, and subsequent evolution.

Planets, which are the most prominent celestial bodies in any solar system, can range from rocky, terrestrial worlds to gas giants, depending on their location in the protoplanetary disk and the materials available during their formation.

Varied Cast of Characters

In addition to planets, moons orbit around planets, adding complexity to the system. Asteroids and comets represent the leftover building materials from the solar system's formation. Finally, the presence of a central, sustaining star is crucial, as it governs the dynamics of the system, the distribution of celestial bodies around it, and ultimately, the potential for life on these worlds.