Where did Ransom end up at the end of chapter 3

Confused, Ransom sits back on his bed and wonders about his situation. He looks once more through the skylight at the giant orb, which he realizes is much too large to be the full moon. Just then, a door opens and Weston walks in. He is nude. Ransom turns to him and confirms that indeed it is not the moon he sees floating in space. It is the Earth.