Here is the full list of all 19 Gravity Ghost achievements.
Terraform 100 planets
Terraform the biggest planet in the game
Make 10 gem planets
Beat the game
Collect all 94 stars
Reunite all animals, collect all geoms, collect all stars
Reunite all 14 animals
Collect all 7 geoms
Make 10 ice planets
Make 10 fire planets
Make 10 air planets
Make 10 earth planets
Make 10 water planets
Reach max hair length
Float for 10 minutes without touching the ground
Carry all 14 animal spirits at once
Carry all 7 planet pieces at once
Carry all animal spirits and planet pieces at once
Speedrun the game in less than 50 minutes