Here is the full list of all 15 Jettomero: Hero of the Universe achievements worth 1,000 gamerscore.
Used a volcano to launch into space
Destroyed the enemy base
Destroyed 5 imposters
Chose to live or die
Unlocked all back issues
Collected all parts
Reached the secret system
Destroyed a comet
Searched rubble for survivors
Extinguished a forest fire
Chased a storm away
Obliterated a moon
Destroyed 25 asteroids
Defeated a Monster
Dove into the sun