AbstractAmong various factors affecting the space weather effects of a coronal mass ejection (CME), its propagation trajectory in the interplanetary space is an important one determining whether and when the CME will hit the Earth. Many direct observations have revealed that a CME may not propagate along a straight trajectory in the corona, but whether or not a CME also experiences a deflected propagation in the interplanetary space is a question, which has never been fully answered. Here by investigating the propagation process of an isolated CME from the corona to interplanetary space during 12–19 September 2008, we present solid evidence that the CME was deflected not only in the corona but also in the interplanetary space. The deflection angle in the interplanetary space is more than 20° toward the west, resulting a significant change in the probability the CME encounters the Earth. A further modeling and simulation‐based analysis suggests that the cause of the deflection in the interplanetary space is the interaction between the CME and the solar wind, which is different from that happening in the corona.
