Discoveries are a sort of catch-all of stuff that doesn’t fit into the other categories. In the playtest, the PCs recently came upon what they figured out was a sort of underground hovertrain. Getting it to function (sort of) was the subject of most of a session, and turned out to be interesting and even thrilling all by itself. This was a discovery. It’s not an artifact they’ll be able to claim as their own, and while it’s useful it doesn’t make their characters more powerful.