 What emotions could likely be behind the expression on Peter's face at the end of the passage when he was told that they could not return to Earth?
I do not think it was what Peter called an emotion; and yet it had nothing to do with logic, either. They have treated us precisely as we, in less enlightened days, might have treated a newly-discovered race of lower animals. They have examined us, dissected us, driven us mad, killed us with no discernable provocation; and this is more intolerable than any normal invasion. "I have no fear that the people of Earth will fail to meet this challenge, for there is no alternative. Not only our individual lives are threatened, but our existence as a race. Peter took it in fifteen seconds, running, and stumbled to a halt in front of the door marked "Radiation."
 Defeat
 Fear  Satisfaction  Defeat  Contentment