And as the frontiers of knowledge and discovery move on, the search for a pale blue dot continues.

The most important and most admirable problem that there is.

Tom Daniels tiptoed down the shadowy concrete corridor toward the door marked STAFF ONLY.

This is cool, he said to himself. Like a spy or a detective or something.

He was celebrating his fifteenth birthday in his own way. All summer long he’d been stuck here at the observatory. His father had said it would be fun, but Tom wished he’d stayed back home with Mom and all his friends. There weren’t any other kids at the observatory, nobody his own age anywhere nearby. And there wasn’t much for a bright, curious fifteen-year-old to do, either.

He remembered last summer, when he’d stayed home with Mom. At least at home I could go out in the backyard at night and look at the sky. He remembered the meteor shower that had filled the night with blazing streaks of falling stars.

No meteor showers here, he thought. Not this summer. Not ever.

Sure, Dad tried to find busywork for him. Check the auxiliary battery packs for the computers. Handle the e-mail going back to the university. If that was fun, Tom thought, then having pneumonia must be hysterical.

There was one time, though, when Dad let him come into the telescope control center and look at the images the big ’scopes were getting. That was way cool. Stars and more stars, big groady clouds of glowing gas hanging out there in deep space. Better than cool. Radical.

That was what Tom wanted. To be in on the excitement. To discover something that nobody had ever seen before.

But Dad was too busy to let Tom back into the control center again. He was in charge of building the new telescope, the one that everybody said would be powerful enough to see Earth-sized planets orbiting around other stars. Other worlds like Earth.

All the observatory’s telescopes were searching for planets circling around other stars. They had found plenty of them, too: giant worlds, all of them much bigger than Earth. None of them had an ocean of blue water. None had fleecy white clouds and an atmosphere rich with oxygen. No “pale blue dot” like Earth.

Dad said this new ’scope just might be able to find a pale blue dot out there among the stars: a pale blue dot like Earth.

So Tom tiptoed to the locked steel door, all alone in the middle of the night, determined to celebrate his birthday in his own way.

He had memorized the lock’s electronic code long ago. Now he tapped the keypad set into the concrete wall and heard its faint beeps. For a moment nothing happened, then the door clicked open.

What if somebody’s in the control center? Tom asked himself. What if Dad’s in there? I’m supposed to be asleep in my bunk.

He shook his head. None of the astronomers worked this late at night unless something special was going on. The big telescopes outside were all automated; the computers collected the images they saw and recorded all the data. Only if something unusual happened would anybody get out of bed and come down here.

He hoped.

Pushing through the heavy steel door, Tom saw that the control center really was empty. Even the ceiling lights were off; the only light in the cramped little room came from the computer screens, flickering off the walls in an eerie greenish glow.

The big display screen on the wall showed the telescopes outside, big spidery frameworks of steel and aluminum pointing out at the black night sky.

His heart thumping faster than usual, Tom went straight to the console where the new telescope was controlled. He sat in the little wheeled chair, just as his father would. For a moment he hesitated, then, licking his lips nervously, he booted up the computer.

“Happy birthday to me,” Tom whispered as the screen lit up and showed a display of icons.

Dad’s going to be pretty sore when he finds out I used the new ’scope before anybody else, Tom thought. But if I discover something, something new and important, maybe he won’t get so mad. Maybe I can find the pale blue dot he’s been looking for.

Tom knew the telescope was already focused on a particular planet orbiting a distant star. He leaned forward in his chair and pecked at the keyboard to get some pictures on the screen. Up came an image of the planet that was being observed by the new telescope: a big slightly flattened sphere covered with gaudy stripes and splotches of color. Along the bottom of the screen a data bar showed what the telescope’s sensors had determined: the planet’s size, its density, the chemical elements it was made of.

Tom saw that the planet was a lot like Jupiter, but much bigger. A huge gas giant of a planet, without even a solid surface to it. So very different from Earth. Seven hundred light years away. He calculated quickly in his head: That’s forty-two trillion miles. I’m seeing this planet the way it looked seven hundred years ago; it’s taken light that many years to cross the distance from there to here.

Then his breath caught in his throat. From behind the curve of the planet’s rim, Tom saw something new appearing.

A moon, he realized. It had been hidden behind the planet’s huge bulk. Glancing at the data bar he saw that this moon was almost the same size as Earth. And it gleamed a faint, soft blue.

A pale blue dot! As the distant moon moved clear of the planet it orbited, Tom saw a world that looked like Earth.

He yanked the phone from its holder and punched out his father’s number. “Dad! Come quick! Quick!”

Before his father could ask a question Tom hung up, bent forward in his chair, staring at this distant blue world.

Then he looked again at the data bar. This world showed no water. No oxygen. The blue color was from methane, a deadly unbreathable gas.

His father burst into the data center. “What is it, Tom? What’s wrong?”

Feeling almost ashamed, Tom showed him the display screen. “I thought I’d found a world like Earth,” he said, crushingly disappointed.

“What are you doing in here?” his father demanded. “You ought to be in bed, asleep.”

“I. . .” Tom took a deep breath. “I’m celebrating my birthday.”

“Your birthday? That’s not until tomorrow.”

“It’s past midnight, Dad.”

Dad’s frown melted slowly into a smile. “Yes, so it is. Well, happy birthday, son.”

“Thanks, Dad.”

“I had a surprise party arranged for you,” Dad said, almost wistfully. “With a videophone call arranged from your mother and sister.”

Tom tried not to laugh. “I guess I surprised you, instead.”

“I guess you did.”

Dad spent almost half an hour studying Tom’s discovery.

“Well, it’s not like Earth is now,” he said at last, “but Earth had a lot of methane in its atmosphere a few billion years ago.”

“It did?” Tom brightened a little.

“Yes, back when life first began on our world.”

“So this world is like ours was, way back then?”