 Of the following, which is the best plausible explanation for the behavior of the Earthen ships?
If Procyon had possessed a habitable planet, we could have returned after an absence of not much over twenty years Earth time. "One week since we passed close enough to Aldebaran to ascertain that that system, too, is devoid of planets. "We face the unpleasant realization that what was feared is probably true—that worlds such as the Sun's are a rare accident, and that we may complete our search without finding even one new Earth. Certainly the building of this ship and its two sisters, the immense expenditure of time and labor and energy stores that went into them, left Earth's economy drained and exhausted. "That was why the planners limited our voyage, and those of the other Quests , to less than a thousand years Earth time.
 900 years passed on Earth. The populations were different enough that the Quest III Earthens scared the current Earthen population.
 Since the Quest III trip promised to locate more planets, the current Earthens didn't trust them when they learned of their success because of how unlikely it was.  Since the Quest III trip promised to locate more planets, the current Earthens didn't trust them when they learned of their failure.  Since the Quest III trip promised to locate more natural resources, the current Earthens didn't trust them when they learned of their failure.  900 years passed on Earth. The populations were different enough that the Quest III Earthens scared the current Earthen population.