ZeniMax, Bethesda's parent company, filed a couple of trademarks for "Starfield" three years ago (ranging from console and PC games to merchandise). They never gave us any clue as to what this project could entail, and since three years went by without a word, its relevance faded away. That is, until now, because ZeniMax has filed a fourth trademark for Starfield, this one for mobile games. So maybe Starfield is really going to be one of Bethesda's future projects.
Because of the title, I can't stop imagining an RPG in the style of The Elder Scrolls and Fallout, but in a science fiction setting, with various space stations instead of the inhospitable Wasteland or the cold mountains of Skyrim. The mobile trademark could mean there will be a tie-in like Fallout Shelter, which wouldn't be a bad idea, since Fallout Shelter did quite well. Anyhow, for now this remains all just speculation, but maybe we'll see an announcement at E3 next month.