Manager Eric Wedge said Aardsma threw well and will now work two simulated innings of about 15 pitches each on Friday in Kansas City. If all goes well there, he'll likely be sent out on a rehab assignment in the Minor Leagues before returning to the Mariners.
Wedge didn't set a timeline, but he noted that as a late-inning reliever, Aardsma won't need as much time to get ready as would a starter or long man.
Aardsma pitched to Franklin Gutierrez, Ryan Langerhans and Chris Gimenez on Tuesday and didn't give up any solid contact. Gutierrez lifted one fly ball to right field and Gimenez hit a soft grounder to shortstop.
Wedge said that when Aardsma is ready, he'll return as the closer.
"That's his mentality. That's what he is," Wedge said. "As long as he's comfortable with it, we are."