Hunter Pence has been in Philadelphia for a couple weeks already, but the Houston Astros didn't decide on who would be the fourth player joining their organization in that trade until today. According to Alyson Footer, that player is outfielder Domingo Santana, as the Astros have announced today that Santana has been selected as the player to be named later in the Hunter Pence trade.
When the Pence deal was originally completed, the Astros acquired Jonathan Singleton, Jarred Cosart and Josh Zeid, but they were also given a list of players that they could select as the "player to be named later" in the trade. It's not clear who was on the list outside of Santana, but it's fair to assume that he was arguably the best player being offered given that the Astros selected him.
Santana, 19, has spent the entire year in Single-A, posting a .269/.345/.434 line in 391 plate appearances. He's a massive guy, standing 6-foot-5, and he has huge raw power, but he's always battled the major contact issues that come with a swing as long as his. Things are no different this year; after striking out in 36% of his PA's last season, he's still striking out at a 31% clip this year, but with significantly less walks. He has massive potential given his power, but he's still extremely raw and is likely to be at least a few years away from MLB playing time. He does give the Astros something they've lacked, though: a position player with star-level upside.