According to reference news, at some time in the future, we may have to leave our solar system. Today, our technology cannot support such a mission, because we have no spacecraft that can overcome the obstacles faced by space travel. But what if we can travel in space without spacecraft? Irina romanovskaya, a professor of physics and astronomy at Houston Community College in the United States, proposed that alien civilizations may use free floating planets as interstellar vehicles to reach and explore other planetary systems. Her research was published in the International Journal of astrobiology. In order to find these alien civilizations, romanovskaya said, "I think that alien civilizations may use the free floating 'wandering planets' as a means of transportation for interstellar migration and colonization. The strategy I propose is to try to find their technical seals and products." So, where do these "wandering planets" come from? Most of them may be "expelled" from their stellar galaxies due to gravitational events, but some may be formed by accretion like stars. In addition, they may also come from the Oort cloud. There is a possibility that in the underground ocean where these "wandering planets" keep warm through radioactive decay, there are life forms that travel on these planets. It is speculated that there may be about 50billion "wandering planets" wandering in our galaxy. Romanovskaya's idea is that, in theory, sufficiently advanced alien civilizations may occupy one of these "wandering planets" and use them to leave the original planet. Although many of these planets are barren "wandering asteroids" that cannot sustain human life, the researcher speculates that some of them may have surface or underground oceans. Coupled with a sustainable atmosphere and a reliable level of gravity, they may become available resources for alien life to travel between stars. Of course, if we want to use these "wandering planets" for interstellar migration, in addition to having the necessary water resources for human sustainable survival, they must also be close enough to our solar system so that we can board them. (Xinhua News Agency)