Peterson, the 12th-overall pick in the 2013 Draft, was Seattle's highest unprotected player as the club's No. 8-rated prospect by MLBPipeline.com, so it's not surprising the Mariners moved him onto the Major League roster rather than risk another team grabbing him in the Rule 5 Draft, which will be held on the final day of the Winter Meetings, Dec. 8, in Washington, D.C.
The two pitchers were added because both are the types of players teams tend to target in the Rule 5 Draft with the idea they might be able to survive a full-season on a 25-man roster.