I think reducing the space would be a great idea, here's some extra feedback:
- also start with the player facing up, I was waiting for the asteroids to appear near the earth, but playing the game again, I realized I could shoot at them when they spawn.
- Also making the turret occupy a little less space on the screen would be a nice idea, maybe make it a little smaller, or zoom in a bit, as with the shooting particles it can occupay half the screen
- Show some arrows where the asteroids are coming from, something like a radar to help guiding the player.
- Is there a final goal to the game?