 Some simulations show that the eccentricity of the system 's planets may have arisen from a close encounter between the outer planet and a fourth planet , with the result that the fourth planet was ejected from the system or destroyed . If so , the rogue planet would have had to eject immediately ; it is unclear how likely this situation might be . Other models are possible . However , a fourth planet ( Upsilon Andromedae e ) was discovered in 2010 . This planet is in a 3 : 1 resonance with Upsilon Andromedae d . 
