For thousands of years, humans have explored (探索) the Earth. Nowadays, we are exploring space. Astronomers (天文学家) are the modern day explorers. Now, many astronomers are looking for new planets and new places for humans to live in the future. But where do astronomers start looking?

First of all, astronomers look for a star. That's because our own Earth moves around a star (the Sun).More importantly, it is the correct distance (距离) from the Sun for heat and light. So when astronomers have found the star, they look at the planets around it. In recent years, astronomers have found nearly 400 new planets with stars. However, many of these planets are either too near the star or too far away.

However, if the planet is in a good position, astronomers look for three key things: water, air and rock. Water is important because all life needs water. Humans can drink it and also grow plants with water. And plants produce air for humans to breathe and food to eat. Rock on a planet is also important. That’s because there is often water under the rock.

After many years of scrutinizing, astronomers have found a planet that is similar to the Earth. It’s Gliese 581g and it’s near a star. The astronomers think it has water and rock and the average (平均) temperature is between－31°C and－12°C. That’s cold, but not colder than Antarctica or the Arctic Circle, for example. Gliese 581g is bigger than the Earth. A year on Gliese 581g is only 37 Earth days instead of 365.But astronomers do not think these are big differences and some of them think Gliese 581g will be a new Earth. However, Gliese 581g is twenty light years from the Earth.

Thousands of miles from the Earth, in outer space, is a small planet, far from the Sun, behind a much bigger planet. Little green aliens live there. They use torches to see.

One day, a young alien, Neila, put the wrong batteries in her torch.

Suddenly, there was bright light. It went up into the sky, around the Sun and reached the Earth.

The light hit a boy called Billy and his dog. Neila quickly turned the torch off, but the pair were caught by the light. They flew through space and landed near Neila.

“ Hello,” said Billy. Neila smiled.

“ Wow!” said Billy, “Everything’s made of ice cream!”

“The ice cream never melts (融化), and nobody eats it. It’s too cold here,” said Neila.

Neila looked sad. “Can you help us?” she said, “We need sunshine to make things grow.”

“No problem,” said Billy, “Can you get us home? I have an idea.”

“Wait there!” said Neila.

She got her torch, put the wrong batteries in again—ZOOM! Billy and his dog flew back to the Earth.

Billy pointed his bedroom mirror between the Sun and Fliptune. The sunlight bounced off the mirror and up onto Neila’s planet.

Thanks to Billy, Fliptune is not cold any more. Billy moves the mirror every day to keep the sun shining there. Now Neila and her friends sit in the sun and enjoy all the free ice cream.

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