Here is the full list of all 17 Planet Nine achievements.
Complete main mission 1
Complete main mission 2
Complete main mission 3
Complete main mission 4
Complete main mission 5
Complete main mission 6
Complete Main mission 7
Complete Main mission 8
Complete Main mission 9
Complete Main mission 10
Complete Main mission 11
Complete the Gauntlet
Brought a skill to level 4
Brought a skill to level 8
upgraded item to max level
Changed locomotion on mech