Question

Which statements describe planetesimals? Check all that apply. They are the origins of planets. They formed from gas and dust. They were created during the big bang. They are believed to have developed in debris disks. They contain 98 percent of matter in the solar system.

Answer 1

They are the origins of planets.

They formed from gas and dust.

They are believed to have developed in debris disks.

Answer 2

They are the origins of planets.
They formed from gas and dust.
They are believed to have developed in debris disks. 

According to the planetesimal theory, planets were formed from planetesimals. It all started with gas and dust-- remnants of the big bang in the form of debris disks. These disks coalesced and formed bigger and more solid forms of matter through the process of accretion.  

These bigger forms of matter ten started to attract each other as they grew bigger due to gravity. They slammed into each other, either breaking smaller pieces apart or they stuck together to form even bigger pieces. These became planetesimals. As the collisions continued, the others became bigger and bigger and formed planets.