"Because he was germ-free?" I suggested.
"It's possible. Or his medical science may have gotten oral bacteria under control with drugs. Maybe he preserved his teeth by diet, or with fluorides in his drinking-water. Perhaps his mother never let him eat candy when he was a kid," Dorsey said. "Who knows? Good teeth and all, though, our Immermann Man died twenty thousand years ago. Why? Was he germ-free, as you suggest; and was he killed by some species of Martian micro-organism that's since gone extinct from drought and a shortage of hosts? The big question, to my mind, is why none of our explorers has yet found any sign of the rest of the expedition."
"Expedition?" I asked.
"A man could hardly have been alone on Mars," Dorsey said.
"From where?"
"Pick any 'F'- or 'G'-type star with planets," Dorsey said. "After all, it's easier to posit extra-solar man than to suppose a flint-drive spaceship was devised by some early neolithic von Brauns."
"I'd never expected to see an astrophysicist take off on such a flight of improbabilia," I said.
"John, would you like to hear a thread-recording I just got from the radio observatory at Adelaide?" Dorsey asked.
"Hi-fi?"
"The radio sky is strictly spark-gap quality, no fi at all," Dorsey said, getting up to lead the way from the dining-room. "This transmission you're going to hear doesn't have anything to do with the ordinary 21.12-centimeter neutral-hydrogen radiation; but of course you realize that our big paraboloid bowls can catch anything from hydrogen hiss to low-flying bats. Remember the Christmas celebration at New Caanan that was telecast to earth a couple years back? That show was caught by the six-hundred-foot receiver at Green Bank, West Virginia, and rebroadcast by C.B.S."