The images, clockwise from the top left, were taken on August 5, July 28, August 2, and August 1.
Radar illumination is from the top and the asteroid's rotation is clockwise.
The Goldstone images taken on July 28 have a vertical resolution of 38 meters per pixel and those taken on August 1 have a vertical resolution of 19 meters per pixel. The images taken by the Arecibo Observatory on August 2 and 5 have a vertical resolution of 15 meters per pixel. However, although collisions are thought to be the primary process determining asteroid spin states, astronomers do not know how these slow, complex rotation states come about. 1999 JM8 was discovered with a United States Air Force telescope in New Mexico that is part of MIT's Lincoln Near Earth Asteroid Research project. The Planetairy Socety.