"Red Planet Nocturne" (sad piano)
If you play anything in minor on the higher octaves of a piano, it sounds bittersweet. Especially if you’ve been reading Steins;Gate, where they have multiple piano arrangements of the main theme that they use for bittersweet moments.
The original “Red Planet Nocturne” is the theme for the game Offworld Trading Company, a colonization / resource management game. The composer is Christopher Tin, who did my favorite modern orchestral album, Calling All Dawns.