A planet or station can only be selected if it is annotated with its name. This annotation is only performed when the game assumes that the object is clearly visible. The heuristic that is used for this decision sometimes fails badly. Therefore some planets can only be selected if the system is zoomed <#36#>and rotated<#36#> until the observer's position is near the planet. Try it with Pluto in Sol [0, 0]. It really is selectable!