Question

what are planet decimals

Answer 1

These were the objects that first formed, mostly in the inner solar system, as the dust and gas nebula collapsed. The planetisimals would then stick together, through soft collisions, until they grew big enough to have sufficient gravity to attract even more stuff, allowing them to grow into planets. The term "planetesimal" is used for objects that become just big enough for their own gravity to begin to help in the gathering of other "stuff". Once the object gets big enough from gravity to become the principal agent of collection AND when the body itself begins to differentiate due to its own gravity (meaning: heavier stuff begins to drift towards the middle of the object), then they are called protoplanets. There is no clear division line between planetesimal and protoplanet. The theory that includes planetesimals, in the formation of planets, was originally from Viktor Sergeevich Safronov, a Soviet astronomer.