This market will predict the total known human population living outside the volume contained by Earth's natural atmosphere at the end of the year 2030. The market will resolve based on the most authoritative and widely accepted report or data source available after December 31, 2030, which provides the total estimated off-Earth human population on that date. The market pertains only to the known human population living outside the volume contained by Earth's natural atmosphere and does not account for any potential discrepancies due to unknown or uncounted populations.

Edit: My go-to source for now is https://www.howmanypeopleareinspacerightnow.com