This seems to be a common view of the title, even though "Planet Explorers" can also accurately mean "Explorers whom explore a planet".
As for the range of the game, the devs were aiming to be able to at least explore one of Maria's moons. This will likely be coming in a later expansion, if the devs are still seeking this goal. Space travel though will not be possible with the structure of PE.
PE is certainly still being worked on, but the development team is also working on other projects alongside it, so updates will be coming a bit more slower than they used to.