介绍：Escape velocity: the minimum speed needed for an object to escape from the gravitational influence of a massive body, without ever falling back. An astronaut awakens in an abandoned cave of a strange planet. An interstellar vagabond, so to say. A light path leads him to the surface, where he looks at his compass and heads for his spaceship. He keeps glancing back, treading nervously, looking afraid. He has been chased by a creature for a long time, and his only way to break free is to escape this curious planet.