"Were you made by other beings, or did you evolve on your own?" asked the youngest Pet, a spotted biped named 34355011 — or plain "Dirrei" to his friends. The question was relayed to the three planets, and since Dirrei stood on Mars, it was Mars who received it first.

"Mind your own business," grumbled Mars. "Just because I let you walk on me..."

Jupiter replied: "Both. It wasn't planned, from what I can remember, but merely turned out that way. I remember I was once subdivided into many billion parts, who called themselves Immortals, and over time they came together in neural networks to form me, inside the crust of this planet."

"I was always this," added Neptune. "There were never parts of me, only the whole."

"Do you like it here?" asked another Pet, who felt sorry for the planet-sized beings, being trapped by their size, doomed to orbit a dead star until it went completely dark (she told her friends later). "Don't you want to leave, and see the Universe?"

"Go where?" Mars replied. "All stars die. The Universe is old. We have our eyes in the sky. We have seen cultures rise and fall. There is nothing new to see, all is known."

Jupiter fell in: "Speak for yourself, Mars. I want to see other stars. Meet other planets."

"Had enough of us, have you?" snapped Neptune. "If you had to listen to yourself all the time, you would be fed up with it, too."

The three planets started to scream at each other, their transmitted voices multiplied and amplified, filling the empty space between them with electromagnetic waves.

The Runaway Pets decided to leave the Martian surface before the energy transmission levels became harmful to them. They hurried into their landing-ships and took off for the orbiting mothership.

A while later, safely in orbit, the Pets took the mothership closer to the dead red star. The star's outer shell of gas was so thinned out that the ship could move only a few kilometers above it. A vast sea of red billowed faintly past the ship, reflected in the ship's smooth metal hull.

But then, an anomaly was detected near the star's surface. The Pets realized that they had found a planet in orbit very close to the surface. They set course for a flyby of the newfound planet. A ship's day later, the planet came into view. It was larger than Mars, its surface melted smooth and featureless; it resembled a polished ball of marble. The smooth surface reflected everything around it: the dull red glow of the dead sun, the stars in space, the passing mothership.

The Pets gazed in awe at the mirror surface of the planet, a miniature Universe filled with tiny stars and planets.

"I suppose beings like us once lived there," suggested Dirrei. "Before the star burned out and melted the surface into glass."

An elderly Pet said, "There is nothing more for us here. Let us leave this system and find green planets with blue oceans. I want to feel the green stuff under my feet again."

The Runaway Pets agreed.

And so their mothership made one last lap around the dead star, and speeded toward Jupiter for the final slingshot plunge into deep space.

Some hopeful Pets transmitted their friendly goodbye messages to the three planets, who had fallen into silence. Ship-days went by, Pets fell in love and formed new couplings, conflicts were settled, and old Pets died surrounded by their loved ones. The Pets were a tightly-knit flock and thus never alone, even in the emptiness between stars.

As the mothership passed outside the orbit of Neptune, suddenly the planets called out to the visitors.

"Don't leave so soon," pleaded Jupiter. "We can give you things, tell you the secrets of the past, entertain you, feed you. We so seldom get visitors. Please reconsider."

"I may look dry and sterile now," said Mars, "but once I was green all over. I need carbon-based life on my surface, people like you. You can make me green again! You'd be stupid to turn down that offer. Hey!"

"It's no use," said Neptune. "They have outgrown us. They can't bring back the past. They won't make her come back."

Dirrie heard this, and sent back a question, despite his elders' objections. "Who lived on the planet with the mirror surface, the one closest to your sun?"

There was a silence of hours. Then the planets spoke. The three voices melted into a single voice, the way people do each other after too much time in each other's company.

"She was us."

"Our motherworld."

"Now our mirror."

"Into which we look, to remind ourselves of her."

"But in her smooth mirror, we see only us, and how time has passed."

"We thought the memories would be enough."

"We never forget."

"But that only makes it worse."

"So we tried to fill our memories up, until there would be no space left in us to suffer conscious thought. For an eon or two, we scanned space and tried to suck in all knowledge in the Universe."

"But there is a flaw in our structure, built into us from our earliest creation. When our planetary memories were full, the system would automatically erase the oldest memories to make space for recent ones."

"And we lost many precious memories of the motherworld, before we could stop the erasure. Most of our eyes in the sky are now shut down. We have been the way we are for longer than we dare to remember. Each round in orbit is like the last one, instantly forgotten."

The Pets wept, the way large-brained carbon-based bipeds are wont to do, by leaking clear liquid from the mucuous membranes of their eye-organs.

And like their distant ancestors once did, they gathered on a knoll in the park in their ship's habitat cylinder, and began to howl.

All the Pets joined the haunting chorus, and the ship sent their song to the three planets. The dog-howl of Pets young and old, converted to electromagnetic waves, bounced off the mirror- smooth shell of the dead motherworld. And when the howl was reflected by the mirror sphere and sent outward, the three lonely planets heard it. It reminded them of the motherworld, of how she had sung her farewell to them — just before their sun died in a flash of helium fusion.

The song of the lonely planets could be heard for a long time after the Pets left them.