That Distant Star Gate

In the future, human aerospace technology develops rapidly. When humans colonize the solar system, a huge ring-shaped man-made object is discovered in the Kuiper Belt. After decades of research, it is discovered that this is a star gate made by aliens. When humans thought it was a door to a new world, they observed the reasons why aliens built it. There was not much time left for humans. Since then, all humans have embarked on the Great Migration.