Quite suddenly the room seemed hot and stuffy, oppressive. He couldn't make his thoughts come straight. There had been too much thinking, too much speculation. Tom stood up and slipped on his jacket.

He had to walk, to move about, to try to think. He slipped open the door, and started for the ramp leading to the Main Concourse.

There was an answer, somewhere.

He walked on along the steel walkways, trying to clear his mind of the doubts and questions that were plaguing him. At first he just wandered, but presently he realized that he had a destination in mind.

He went up a ramp and across the lobby of the United Nations Administration Building. He took a spur off the main corridor, and came to a doorway with a small circular staircase beyond it. At the bottom of the stairs he opened a steel door and stepped into the Map Room.

It was a small darkened amphitheater, with a curving row of seats along one wall. On either side were film viewers and micro-readers. And curving around on the far wall, like a huge parabolic mirror, was the Map.

Tom had been here many times before, and always he gasped in wonder when he saw the awesome beauty of the thing. Stepping into the Map Room was like stepping into the center of a huge cathedral. Here was the glowing, moving panorama of the Solar System spread out before him in a breath-taking three-dimensional image. Standing here before the Map it seemed as if he had suddenly become enormous and omnipotent, hanging suspended in the blackness of space and staring down at the Solar System from a vantage point a million miles away.

Once, Dad had told him, there had been a great statue in the harbor of Old New York which had been a symbol of freedom for strangers coming to that city from across the sea, and a welcome for countrymen returning home. And someday, he knew, this view of the Solar System would be waiting to greet Earthmen making their way home from distant stars. The Map was only an image, a gift from the United Nations to the colonists on Mars, but it reproduced the Solar System in the minutest detail that astronomers could make possible.

In the center, glowing like a thing alive, was the Sun, the hub of the magnificent wheel. Around it, moving constantly in their orbits, were the planets, bright points of light on the velvet blackness of the screen. Each orbit was computed and held on the screen by the great computer in the vault below.

But there was more on the Map than the Sun and the planets, with their satellites. Tiny green lights marked the Earth-Mars and the Earth-Venus orbit-ships, moving slowly across the screen. Beyond Mars, a myriad of tiny lights projected on the screen, the asteroids. Without the magnifier Tom could identify the larger ones ... Ceres, on the opposite side of the Sun from Mars now as it moved in its orbit; smaller Juno, and Pallas, and Vesta....