What is the chance your plane will be hit by space debris?

MIT Technology Review 

What is the chance your plane will be hit by space debris? Explains: Let our writers untangle the complex, messy world of technology to help you understand what's coming next. In mid-October, a mysterious object cracked the windshield of a packed Boeing 737 cruising at 36,000 feet above Utah, forcing the pilots into an emergency landing. The internet was suddenly buzzing with the prospect that the plane had been hit by a piece of space debris. We still don't know exactly what hit the plane--likely a remnant of a weather balloon--but it turns out the speculation online wasn't that far-fetched. That's because while the risk of flights being hit by space junk is still small, it is, in fact, growing.