Pretty much (the planet eats up 80% of the sprite table in fact). Other objects are also sprites on top of the planet, I was kind of surprised that sprite overflow never happens given how many sprites end up on the same line thanks to the planet.
Planet = miniplanet
Planet set = planelago
Everything = planelago system
Planelago = planet + archipelago :P (a planelago is a group of small planets much like how an archipelago is a group of small islands)