"But the elements of the moon are different—and there's only one explanation."
"What?"
"Think about it a minute, Sam. We take a spectrograph of the sun, and we find the same elements that are here on earth. We turn it on Alpha Centauri and find the same thing. We turn it to the farthest stars we can find that give enough light to record by. Always the same. Calcium is calcium, whether it's on the earth or on a star a half billion light years away."
"So?" Sam's voice was tired, and he sounded as if he was listening only because Jim was too good a friend to tell to go to hell for calling in the middle of the night.
"So? So what?" Sam repeated.
"So we go to the moon," said Jim, "and all of a sudden calcium isn't calcium, and the sodium on the moon isn't the same as the sodium on earth and on the sun and on Alpha Centauri and the stars a half billion light years away. Don't you see what that means!"
"No, I guess not," said Sam dully. "Maybe in the morning—"
"It means the moon just doesn't belong, Sam! It means the moon is completely foreign to anything in the Solar System, in the whole galaxy—in any galaxy we have been able to analyze. It means the moon has come from somewhere else, from a region of space where atoms and electrons are not even the same as atoms and electrons here. It must be a somewhere that's so far away it's beyond the edge of space as we know it!"
"I'll get dressed and come over," said Sam.