Since I upgraded my explorer to find 89% more map pieces, he has never found a SINGLE adventure.
I upgraded that part of the tree and the part that lowers the cost of adventure searches, as well as the part that shortens the time of adventure searches on the first day that the explorer skill trees became available. I don't know what date that was, but it must be at least 25 searches without a single adventure. I don't believe that that is just a coincidence and think that the science system may be bugged