Final answer:
The smaller pieces that clustered together to eventually form the major bodies of our solar system are known as planetesimals. These became the building blocks for planets and remain observable today as comets and asteroids.
Step-by-step explanation:
The material that would eventually make up all the major bodies in our solar system first gathered together as smaller pieces, which astronomers call planetesimals. These planetesimals, chunks a few kilometers to a few tens of kilometers in diameter, became the building blocks of planets through the process of accretion.
The solar system is believed to have formed about 4.5 billion years ago from a massive cloud of gas and dust, which became the solar nebula. As this solar nebula collapsed under its own gravity, the material coalesced and formed planetesimals, some of which can still be seen today as comets and asteroids.