Metallic orb, bowling ball or beach ball sized, and no visible props or motor, flying at approximately 35-40 mph

Walking my dog I looked up and saw a metallic sphere I initially assumed must be a drone, but wondered why it was flying so close to the Ann Arbor airport. As it approached where I stood and flying at perhaps 150-200 feet of altitude, I realized that it had no visible propellers or other means of propulsion and there was no sound. It maintained a steady speed of perhaps 35-40 miles per hour and steady course heading southeast. The entire sighting lasted a minute or less. There were few dogwalkers at the park and no one else seemed to notice.