George's Cosmic Treasure Hunt (27 page)
Read George's Cosmic Treasure Hunt Online
Authors: Lucy Hawking
A
lpha 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 normalâlike 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 coldâthere 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 systemâthe 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 zoneâthe Goldilocks Zoneâof 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
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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.
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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!
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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).
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The fifth planet, Cancri f, is around half the mass of Saturn and lies in the habitableâor Goldilocksâzone of its star. This planet is a giant ball of gasâmostly 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.
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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!
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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.
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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 zoneârunning dangerously low. He looked at George's, but his was still in the green zoneâplenty 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 homeâonly 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.”