Why won't my jump drives let me access this trinary system?

The trinary system in question

I'm relatively new to the game so I understand it's entirely possible I've missed something. But I started as eager explorers and as such have jump drives. Why can't my science OR military ships jump to that trinary system in the middle of my empire?

I only ever get a "there is no known route to this system". Have I missed a tech or something?