What is causing this ring around the outer edge of brake rotor/should I be concerned? mi

It’s only on the rear passenger side, car is pretty new. Less than 9,000 miles on it. Noticed this ring near the outside edge of the rotor the other day. Doesn’t really have any depth to it, yet at least.

It’s only on the rear passenger side, car is pretty new. Less than 9,000 miles on it. Noticed this ring near the outside edge of the rotor the other day. Doesn’t really have any depth to it, yet at least.