Here is the full list of all 15 The Space Garden achievements.
Defeat an UFO
Get your first helper
Collect 100 coins
Get your first plant
Collect 1000 coins
Collect 10.000 coins
Collect 100.000 coins
Place your first face on a planet
Get your first chicken
Get your first guardian
Connect all your planets
Survive to your first alien invasion
Survive to your first zombie attack
Get 100 helpers
Defeat 100 aliens