"They had spaceships?"

"It’s barely possible. I rather hope they did, since it would mean the chance of a survival elsewhere, though the negative results of your expedition rather lessen that." He went on, "The cache was laid down when they were first attempting space flight, just after their discovery of atomic power, in the first flush of their youth. It was probably created in a kind of exuberant fancifulness, with no serious belief that it would ever serve the purpose for which it was intended." He looked at the Explorer strangely. "If I am not mistaken, we have laid down similar caches."