When my grandfather was a boy, Charon had been a site of similar activity. Thousands of excited men and women had clustered around an asteroid ship half the size of the little moon itself, taking aboard a virtual ark of hopeful would-be colonists, their animals, and their goods.

Those early explorers knew they would never see their final destination. But they were not sad. They suffered from no great-depression. Those people launched forth in their so-primitive first starship full of hope for their great-grandchildren—and for the world which their sensitive telescopes had proved circled, green and pleasant, around the star Tau Ceti.

Ten thousand waityears later, I looked out at the mammoth Yards of Charon as we passed overhead. Rank on serried rank of starships lay berthed below. Over the millennia, thousands had been built, from generation ships and hiberna-barges to ram-shippers and greatstrutted wormhole-divers.

They all lay below, all except the few that were destroyed in accidents, or whose crews killed themselves in despair. They had all come back to Charon, failures.

I looked at the most ancient hulks, the generation ships, and thought about the day of my grandfather’s youth, when the Seeker cruised blithely over the Edge, and collided at one percent of light speed with the inner face of Sol’s crystalsphere.

They never knew what hit them, that firstcrew.

They had begun to pass through the outermost shoals of the solar system… the Oort Cloud, where billions of comets drifted like puffs of snow in the sun’s weakened grasp.

Seeker’s instruments sought through the sparse cloud, touching isolated, drifting balls of ice. The would-be colonists planned to keep busy doing science throughout the long passage. Among the questions they wanted to solve on their way was the mystery of the comets’ mass.

Why was it, astronomers had asked for centuries, that virtually all of these icy bodies were nearly the same size—a few miles across?