I have no idea what it was, but I did watch something accidentally clip the edge of Polestar radar cover back in the 90s, entering to the north and heading south-west. Only for about 8-10 radar sweeps before it left cover again. (Running the gap between Rockville and Polestar coverage). M4 slowing and a 3D height coming down through about 150K.
Could have been a comet, but they don’t usually slow down. Who knows?
And what were all those “soap-on-a-rope” contrails way high and fast off the Californian coast?