   (also written (66391) 1999 kw4) is an aten and mercury-crosser asteroid discovered by linear in 1999.  has a moon orbiting it. the moon, designated s/2001 (66391) 1 or " beta", is ~360 m in diameter, and orbits  'alpha' in 0.758 d (16 hours) at a distance of 2.6&nbsp;km. the presence of a companion was suggested by photometric observations made june 19â27, 2000 by petr pravec and lenka Å arounovÃ¡ at observatoÅ ondÅejov (ondÅejov observatory) and was confirmed by radar observations from arecibo observatory from may 21â23, 2001 by lance a. m. benner, steven j. ostro, jon d. giorgini, raymond f. jurgens, jean-luc margot and michael c. nolan, announced on may 23, 2001. the shapes of the two bodies and their dynamics are complex.nasa jet propulsion laboratory asteroid radar research, retrieved may 3, 2007 among other bizarre properties, the equatorial regions of alpha are very close to breakup: raising a particle a meter above the surface would put it into orbit around the object. as seen in the image at above right, the gravitational effects between the moon and the asteroid create a gigantic mountain extending laterally around the entire asteroid. on may 25, 2036 it will pass  from earth. ==references==  * johnston, wm. robert, ed. [
Aten_asteroids Binary_asteroids Earth-crosser_asteroids Mercury-crossing_asteroids Venus-crosser_asteroids