I propose the Cosmic Hitchhikers hypothesis as follows. Advanced extraterrestrial civilizations may use free-floating planets as interstellar transportation for space exploration and interstellar colonization. Large groups or populations of their biological species, post-biological species, and technologies may become Cosmic Hitchhikers when they ride free-floating planets to reach, explore and colonize planetary systems. To get an interstellar ride, Cosmic Hitchhikers may travel to free-floating planets passing close by their home worlds. Otherwise, they may use astronomical engineering to steer free-floating planets toward their home planetary systems. Cosmic Hitchhikers may also ride objects native to the outer regions of their planetary systems, which become free-floating planets when ejected by astronomical engineering or by their stars during the asymptotic giant branch evolution. During interstellar travel, Cosmic Hitchhikers may apply astronomical
engineering to steer their free-floating planets toward the planetary systems of their choice. Whereas riding free-floating planets may not save travel time, it avoids the technical challenges of interstellar spacecraft transporting large populations. Each civilization of Cosmic Hitchhikers may colonize several planetary systems. Its colonies may grow into autonomous civilizations, changing the number of civilizations in the Galaxy. Over the last 4 billion years, Cosmic Hitchhikers or their artifacts riding free-floating planets might have passed by the Solar System. Therefore, their artifacts might exist in the Solar System or in our stellar neighborhood. SETI and SETA should include the search for Cosmic Hitchhikers and their artifacts.
To download the paper, click here.