You only place claims for Earthside missions, which are missions for delivering refineries to existing claims from low Earth orbit. You can get missions other ways, in which case you don't place the claim token. You can also get claims appearing on the map in a variety of ways that don't require prospecting: for instance, every space encounter you have may end up placing a claim on a location.
This Space Intentionally allows you to make claims "the hard way" -- which you need to do if you're not originating in LEO. I should probably state that Earthside missions are only available in the Upported era and later.