resently 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....

For each asteroid which had been identified, and its orbit plotted,
there was a pinpoint of l