Harwich nodded. He remembered very well. Only a hundred hours ago, still on duty as a patrol pilot, he'd seen that pointed mystery from the void, vague dusty movement around its base.
"It was my Dad's guess that whatever miracles are to be discovered on Io, they will probably be located around the Tower," Paul Arnold answered. "But I was careful to notice our position when we landed. We're far north of the Tower now—a good fifteen hundred miles. A nice, long walk—especially when the normal air of the Forbidden Moon is too thin to be breatheable."
"Stop that pessimist stuff, and let's get started!" Harwich snapped. "We'll have to live very primitively, of course, but who knows what will turn up?"
They discarded their parachutes and started out, plodding southward, carrying their heavy packs. As if to save their energy, they did not speak much.
The hills rolled past, under their plodding feet. More fragmentary ruins appeared, and were left behind. Their boots sank into soft dust, as they marched on and on. At first their muscles were fresh, but tiredness came at last. And the miles which lay ahead were all but undiminished.
The tiny sun sank into the west and the cold increased. Night was coming.
"We'd better camp," young Arnold suggested wearily.
So they opened their packs, and took out the carefully folded sections of airtight fabric that composed their tent. It was part of the usual equipment kept for emergency purposes by those in danger of being stranded on dead or almost dead worlds. The tent could be hermetically sealed. Harwich and Arnold set it up carefully and crept inside. Air was freed from their oxygen flask, and the queer shelter ballooned out like a bubble.
They could remove their space suits now, and breathe, here in the tent. They ate sparingly from their concentrated rations. Meanwhile a little pump and separator unit, driven by a tiny atomic motor, was busy compressing the thin Ionian air, separating out the excess of carbon-dioxide and nitrogen it contained, and forcing the oxygen into the depleted air flasks.
Once in the darkness Paul and Evan were awakened by a strange sound, eerie in that dead quiet, and very faint because the scant Ionian atmosphere could not conduct it well. But when they crept to the flexoglass window of the tent, they saw nothing unusual.