by Lucy Hawking
“Um, yes,” George admitted. “We kept going because in each place we found another clue that sent us to a new location.”
“And you came here because the clue you found on Titan told you to go to a binary star system with a planet in orbit around one of the stars?”
“We thought we’d been really smart,” said Annie sadly.
“Oh you have!” said Eric. “All three of you. Emmett believes that the clues are taking you on a hunt for signs of life in the Universe. If he’s right, then we need to find a planet in what we call the Goldilocks Zone of its star. That means a planet that is not too hot, not too cold, but just right.”
“Oh!” said George. “I see—this planet is too hot! So we know this isn’t the right planet.”
“And I can think of another reason to suspect this isn’t the right place. How many stars did the clue show?” asked Eric.
“Two,” said George.
“Here,” said Eric, “there are three. That fainter star, the one you can only just see over there—that’s Proxima Centauri, so called because it’s the closest star to Earth. So this is a triple system.”
“Oh no! Wrong planet, wrong star system,” said George. “What do we do now?”
“So, do you believe us now, about the clues and the messages?” interrupted Annie.
“I do, darling,” admitted Eric. “And I’m so sorry. I’m sure those messages were left for me, not for you. And if I could send you back to Earth right this second, I would. But I can’t do that and I can’t leave you here. So I think we’re going to have to finish the cosmic treasure hunt together. Are you with me?”
Annie moved closer to him. “I am,” she said, “very definitely.”
* * *
ALPHA CENTAURI
At just over four light-years away, Alpha Centauri is the closest star system to our Sun. In the night sky it looks like just one star, but is, in fact, a triplet. Two Sun-like stars, Alpha Centauri A and Alpha Centauri B—separated by around twenty-three times the distance between the Earth and the Sun—orbit a common center about once every eighty years. There is a third, fainter star in the system, Proxima Centauri, which orbits the other two but at a huge distance from them. Proxima is the nearest of the three to us.
Alpha A is a yellow star and very similar to our Sun but brighter and slightly more massive.
Alpha B is an orange star, slightly cooler and a bit less massive than our Sun. It is thought that the Alpha Centauri system formed around one thousand million years before our Solar System. Both Alpha A and Alpha B are stable stars, like our Sun, and like our Sun may have been born surrounded by dusty, planet-forming disks.
In 2008 scientists suggested that planets may have formed around one or both of these stars. From a telescope in Chile they are now monitoring Alpha Centauri very carefully to see whether small wobbles in starlight will show us planets in orbit in our nearest star system. Astronomers are looking at Alpha Centauri B to see whether this bright, calm star will reveal Earth-like worlds around it.
Alpha A and Alpha B are binary stars. This means that if you were standing on a planet orbiting one of them, at certain times you would see two suns in the sky!
Alpha Centauri can be seen from Earth’s southern hemisphere, where it is one of the stars of the Centaurus constellation. Its proper name, Rigel Kentaurus, means “centaur’s foot .” Alpha Centauri is its Bayer designation (a system of star-naming introduced by astronomer Johann Bayer in 1603).
* * *
“Me too,” said George. “Let’s finish this. And find out who is sending those messages.”
“I’m calling the portal,” said Eric. On one side of the crater, they could already see the light of dawn as Alpha B hovered below the horizon. “Emmett!” he called. “Any chance of a trip back to Earth?”
“Not just yet,” said Emmett. “But I do have some reasonably good news….”
“You’ve found us a planet that might be just right, a planet about the size of Earth in the Goldilocks Zone?”
“Affirmative,” said Emmett rather weakly. “Or at least, we’ve found something. It’s our best guess. It’s a moon, not a planet, though.”
“How is Cosmos holding up?” asked Eric.
“I just want you to know,” Mabel chipped in, “that I promised George’s parents I wouldn’t let him get into any trouble during his vacation! I’m going to have a very difficult time explaining this to Terence and Daisy….”
“Cosmos is functioning,” said Emmett nervously. “I’ve nearly finished updating the reverse portal. I’ll be able to bring you in as soon as I’ve finished. Can you wait and I’ll get you back to Earth?”
Bright rays of light were stealing across the crater, chasing the dark shadows away.
“No, we can’t stay here any longer,” said Eric. “Send us onward, Emmett. And don’t worry, Mabel. We’ll be back.”
* * *
THE USER’S GUIDE TO THE UNIVERSE
THE GOLDILOCKS ZONE
Our Milky Way Galaxy contains at least one hundred billion rocky planets. Our Sun has four: namely, Mercury, Venus, Earth, and Mars—but only Earth has life.
What makes Earth special?
The answer is water, especially in its liquid form. Water is the great mixer for chemicals—breaking them apart, spreading them out, and bringing them back together as new biological building blocks, such as proteins and DNA. Without water, life seems unlikely.
To support life, a planet’s temperature must be between 32 and 212 degrees Fahrenheit (0 and 100 degrees Celsius) to keep the water in liquid form.
A planet orbiting too close to its home star will receive so much light energy that it will heat up to scorching temperatures, boiling all the water into steam.
Planets too far from their star will receive very little light energy, keeping the planet so cold that any water will remain as ice. Indeed, Mars has its water trapped as ice at the north and south poles.
There is a certain distance from every star where a planet receives as much light as it emits heat. That energy balance serves as a thermostat, keeping the temperature lukewarm—just right to keep the water liquid in lakes and oceans. In this “Goldilocks Zone” around a star, any planets would stay warm and bathed in water for millions of years, allowing the chemistry of life to flourish.
Geoff
* * *
Chapter 15
Alpha B was rising as they went through the portal, shining brilliantly onto the hot, heavy planet. To avoid having to stand up again, they wriggled feetfirst through the doorway, with Eric hopping up as soon as he was through to pull the two kids after him.
They got to their feet and found they could stand up on the rocky surface of this new place. They didn’t float off it, and they weren’t squished down toward it. It just felt normal—like they could move easily again, without ropes and without having to crawl around.
The light was pleasant, shining from a star in the sky that looked a bit like the Earth’s Sun. It wasn’t too bright, but it also didn’t seem too cold—there was no ice on the rock as there had been on Mars and Titan. In the distance they heard a gurgling, rushing sound. They seemed to be at the bottom of a rocky valley.
“What’s that noise?” said Annie. “And where are we? Are we back on Earth?”
“It sounds like water,” said George, “but I can’t see it anywhere.”
“We’re in the 55 Cancri star system,” said Eric. “It’s a binary star system—the one you see shining in the sky is a yellow dwarf star, just like our Sun. Farther away there is a red dwarf star as well.”
Emmett joined in from Earth. “You are on a moon of the fifth planet around 55 Cancri A,” he said. “The planet is in the habitable zone—the Goldilocks Zone—of its star, but the planet itself is a gas giant, about half the size of Saturn, so I didn’t think you’d want to land there.”
“Well done, Emmett,” said Eric. “I don’t really feel like falling through layers of gas. Not today, anyway. You made a good
choice.”
* * *
55 CANCRI
55 Cancri is a star system forty-one light-years away from us in the direction of the Cancer constellation. It is a binary system: 55 Cancri A is a yellow star; 55 Cancri B is a smaller, red dwarf star. These two stars orbit each other at one thousand times the distance between the Earth and the Sun.
On November 6, 2007, astronomers discovered a record-breaking fifth planet in orbit around Cancri A. This makes it the only star other than our Sun known to have as many as five planets!
The first planet around Cancri A was discovered in 1996. Named Cancri b, it is the size of Jupiter and orbits close to the star. In 2002 two more planets (Cancri c and Cancri d) were discovered; in 2004 a fourth planet, Cancri e, which is the size of Neptune and takes just three days to orbit Cancri A. This planet would be scorchingly hot, with surface temperatures up to 2,732 degrees Fahrenheit (1,500 degrees Celsius).
The fifth planet, Cancri f, is around half the mass of Saturn and lies in the habitable—or Goldilocks—zone of its star. This planet is a giant ball of gas—mostly made of helium and hydrogen, like Saturn in our solar system. But there may be moons in orbit around Cancri f or rocky planets within Cancri’s Goldilocks Zone where liquid water could exist on the surface.
Cancri f orbits its star at a distance of 0.781 astronomical units (AU). An astronomical unit is the measure of distance that astronomers use to talk about orbits and distance from stars. One AU = 93 million miles, which is the average distance from the Earth to the Sun. Given that there is life on Earth and liquid water on the surface of our planet, we can say that one AU, or 93 million miles, from our Sun is within the habitable zone of our Solar System. So for stars of roughly the mass, age, and luminosity of our Sun, we can guess that a planet orbiting its star at around one AU might be in the Goldilocks Zone. Cancri A is an older and dimmer star than our Sun, and astronomers calculate that its habitable zone lies between 0.5 AU and 2 AUs away from it, which puts Cancri f in a good position!
It is very difficult to spot multiple planets around a star because each planet produces its own stellar wobble. To find more than one planet, astronomers need to be able to spot wobbles within wobbles! Astronomers in California have been monitoring 55 Cancri for more than twenty years to make these discoveries.
© NASA/JPL-CALTECH/SCIENCE PHOTO LIBRARY
Artwork comparing the sizes of the 55 Cancri system (left) with a small brown dwarf star system in the constellation of Chamaeleon (upper right).
* * *
The kids stretched out their arms and legs. It felt good to be able to move freely again.
“Can we take our space helmets off now?” asked Annie.
“No, absolutely not!” said Eric. “We have no idea what the atmosphere is made of here. Let me check your oxygen gauge.” He looked at her air tank and saw that it was getting close to the red zone—running dangerously low. He looked at George’s, but his was still in the green zone—plenty still in there. Eric said nothing but called Emmett again. “Emmett, how long before we can return to Earth?”
“I’m getting hungry,” moaned Annie. “Do you think there’s anything to eat here?”
“I don’t think they have restaurants at the end of Universe,” said George.
“We’re not at the end of the Universe yet,” said Eric, while waiting for Emmett’s reply. “We’re nowhere near. We’re still really quite close to home—only forty-one light-years away! We haven’t even left our own Galaxy yet. In terms of the Universe, this is like George coming to the States. A bit of a journey, but hardly an epic voyage.”
“What about the clue?” said George. “Don’t we need to see if there’s another clue here for us? I mean, aren’t we supposed to be saving planet Earth from someone who wants to destroy it?”
“Hmm…” Eric was looking anxious. Emmett was silent. “I think whoever sent you those messages put that part in to scare you,” he said. “I can’t think of anything right now that is powerful enough to destroy a whole planet. It would take far more energy than we’ve ever generated before to blow up the Earth. That was just a threat, to make sure we didn’t ignore the messages.”
“But what if it came from aliens who have sources of power we can’t even dream of?” asked Annie. “How do you know there isn’t a superrace out there? Those messages weren’t sent by some bacteria, were they?”
“That, I suppose,” said Eric, “is what we’re trying to find out. Annie”—his tone changed—“why don’t you sit down and have a rest? Try not to talk for a few minutes, get your strength back.”
“But I don’t want to not talk,” said Annie. “I like talking. That’s what I’m good at. And soccer. I’m good at soccer. And physics. I’m great at that, aren’t I, Dad?”
“I know,” said Eric soothingly. “But you’re running a bit low on air now. So I need you to be quiet for me, until we know when we’re going home.”
George looked around. He studied the ravines and mountains of this rocky planet, seeking the source of the rushing noise. Suddenly, at the other end of the valley, he saw something move.
“Over there!” he said quietly to Eric while Annie sat down on a rock.
“It’s moving,” muttered Eric, spotting it. “But what is it?”
The thing was in shadow so they couldn’t even make out its shape. All they could see was that it was coming toward them. It was like a black blob creeping ever closer.
“George,” said Eric, “call Emmett now! Tell him we’ve got an ET sighting, and I want him to open the portal and take you and Annie back immediately.”
“Emmett…” George tried to call him. “Emmett…Come in, Emmett…Emmett, we need you to beam us up.”
The shape was approaching them along the dark side of the ravine, shaded from the rays of the yellow dwarf star, Cancri A. As it crept toward them, they noticed two tiny pinpricks of bright red light shining from its middle, like a pair of very angry eyes.
“Annie,” said Eric, “stand up and get behind me. We have an alien approaching.”
Annie got to her feet and hurried behind her dad, peeping around him. The black shape came closer, the red lights in its middle sparkling with demonic fury. As it approached, they could see it was shaped almost like a human being, dressed entirely in black, with scarlet eyes burning out of its stomach.
“Get back,” said Eric. “Whatever you are, do not take another step toward us.”
The thing took no notice of Eric’s warning and continued onward. It stepped out of the shadow and into the light. And then it spoke.
“So, Eric,” its voice rasped through all their voice transmitters, “we meet again.”
Chapter 16
OMG! It’s Reeper!” shouted Annie and George at the same moment.
Standing in front of them, in a black space suit with a black glass visor on a black space helmet, was none other than Eric’s nemesis, Dr. Graham Reeper, the once-upon-a-time friend and colleague who had turned on him and become his deadly enemy.
Not so long ago, Eric had let Dr. Reeper, who had been posing as a teacher at George’s school, escape to start a new life somewhere else. Even though he had tried to throw Eric into a black hole and steal his amazing computer, Eric had been convinced that Reeper shouldn’t be punished.
And now it seemed that Eric had made a terrible mistake. Reeper was back and—in his black suit on this distant moon—a thousand times scarier than when George and Annie had last seen him.
Reeper wasn’t alone, either. In his cupped hands he held what looked like a small animal with glowing bright red eyes. Its little paws scrabbled against the shiny black material of Reeper’s space gloves.
“Ahhhh—look!” said Annie. “He’s found a lovely little furry pet on this planet!” She took half a step forward, but Eric shot out an arm to stop her from going any closer. The creature in Reeper’s hands hissed and bared its teeth. Reeper stroked its head with one hand.
“There, there,” he said soothingly. “Don’t
worry, Pooky. We’ll get rid of them very soon.”
“You’ll never destroy us, Reeper,” said Eric defiantly. Behind him, George was desperately trying to radio Emmett.
“Is that the boy?” asked Reeper idly. “Is that the boy who ruined all my plans last time? How kind of you to bring him too. That’s so”—the animal made a nasty growling noise—“thoughtful. And your daughter. How charming.”
“Reeper, you can do anything you want to me,” said Eric, “but don’t touch the kids. Let them go.”
“Let them go?” said Reeper, as though considering it. “What do you say, Pooky?” He scratched the animal’s head. “Shall we let the kids go?” Pooky hissed loudly. “The problem is,” he explained, “your children don’t have anywhere to go. Or any way to get there. I know you’re trying to call your dear chum Cosmos to help you out, and it’s really very touching how much faith you’ve put in him. But you might as well save your oxygen because Pooky here is sending out a very powerful blocking signal.”
“What!” exclaimed Eric. “What is Pooky?”
“Dear little Pooky,” said Reeper. “He is my friend. Sweet, isn’t he? Twice as powerful as Cosmos and so very much smaller. In fact, you could say Pooky is the nano-Cosmos. I disguised him as a hamster. After all, who would think of looking for a very powerful supercomputer inside a hamster’s cage?”
“What!” said Eric. “You built a new version of Cosmos?”
“What did you think I’d been up to all this time?” Reeper sneered. “Did you think I would just forget about everything that happened? Or did you think I would forgive?” He said the last word in a particularly unpleasant fashion. “Forgiveness is only for lucky people, Eric. People like you. People who get everything they ever wanted. It’s easy for you to be forgiving, with your wonderful career and your lovely family and your nice home and your helpful supercomputer. You’ve always had everything your own way. Until now, that is.”