It was the size of a volleyball with a shiny silver surface. it came from the north over highway 89 southbound into flagstaff. it flew overhead roughly between milepost 431 and 430. at first i thought it was a mylar balloon until i noticed it didn't have a tarnished surface and there was no design on the surface. before it crossed the traffic median and over highway 89 north, it slowed down, made a j like turn and proceeded ne. i was driving, so unfortunately i didn't take a picture.