 The system is not coplanar , with each other or with the stellar rotation . The mutual inclination between c and d is 30 degrees . In 2001 , preliminary astrometric measurements suggested the orbit of the outermost planet is inclined at 155 @.@ 5 ° to the plane of the sky . However , subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterize the orbits of substellar companions . Astrometry of the innermost planet , meanwhile , constrained its inclination to 30 @-@ 90 degrees . Full publication is expected in 2008 . The orbit of Upsilon Andromedae c gradually oscillates between circular and eccentric states every 6 @,@ 700 years . The existence of further planets too small or distant to detect has not been ruled out , though the presence of Jupiter @-@ mass planets as close as 5 AU from Upsilon Andromedae A would make the system unstable . 
