Space wallpaper (background of main menu):
https://wallpaperaccess.com/4k-nebula
Used this to convert the nebula into pixelart, which helped ensure the continuity of the pixelart-game experience:
https://pixelartify.com/editor
Spaceship sprites etc:
https://www.deviantart.com/almalakarma/art/space-1046559273
Planet sprites:
https://www.deviantart.com/cluly/art/Planet-Assets-771586986
Asteroids that explode:
https://foozlecc.itch.io/void-environment-pack
Font:
https://fonts.google.com/specimen/Press+Start+2P
Coin: