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