Use of prepositions: on or at?

[Carvalho]

Hi, in this sentence should we say:

Set on a Future Earth where robots are common...
Set at a Future Earth where robots are commo...
Thank you in anticipation

[Jamie (K)]

On.

"At" would make it sound like the story happened next to the earth but not on it, maybe floating in space or something.

[HamburgEnglish]

Set in a Future Earth where robots are common...
Set around a Future Earth where robots are common...
Set over a Future Earth where robots are common...
Set next to a Future Earth where robots are common...
Set away from a Future Earth where robots are common...
Set across a Future Earth where robots are common...
Set outside a Future Earth where robots are common...

CONTEXT ???????????????????????????????