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strapped into your seat. With six seconds before liſt off , the main rocket engines fire. T ey roar. T ey rumble. Everything starts to shake. T e countdown winds down—5, 4, 3, 2, 1.


Liſt off . T e rocket shoots up, pressing you into your seat. Hang on! You’re on a tour of our solar system. Your

super-fast rocket will blast off to the sun. T en you’ll pick up speed and tour the eight planets that orbit the sun. T ey make up our neighborhood in space.

Our Star You head to the center of our solar system. Your destination is a yellow star, our sun. Like all stars, the sun is a ball of hot, glowing gases. T ese gases churn, sizzle, and pop. You can’t land on the sun, though. T e

surface of the sun isn’t solid. T is is a place of bubbling gases and raging heat. All this activity is important. T e sun’s light

and heat spread throughout the solar system. A tiny amount of this energy falls on each planet. Without the sun, life on Earth couldn’t exist. T e sun is the biggest and hottest object

in our solar system. If the sun were hollow, a million Earths could fit inside it. Temperatures in the core soar to 15 million degrees Celsius (27 million degrees Fahrenheit). T at’s not all. T e sun also holds our solar

system together. Without its powerful gravity, our planetary neighborhood would fall apart. T e sun’s gravity is a natural force that pulls the planets toward the sun. It keeps the planets from spinning off into space. T e first four planets from the sun are called

the inner planets. Mercury, Venus, Earth, and Mars are all small and rocky worlds. T e next four planets are called the outer

planets. Jupiter, Saturn, Uranus, and Neptune are huge, cold balls of gases. Because of their large size, they are called gas giants. As you make your tour of our solar system, take a closer look at each planet.


our rocket is on the launch pad, and you’re

The First Planet T e sun’s nearest neighbor is Mercury. It’s the smallest planet. If you look out your rocket window, you’ll see that Mercury is pitted and scarred. Craters dot its surface. Mercury’s surface is also wrinkled. T at’s

because the planet used to be bigger. T en its core cooled a little and shrank. T is made its crust fold in places, forming ridges or wrinkles. If you’re feeling a little warm on Mercury,

it’s because the temperature can get hot. It can also get really cold. Mercury has the greatest temperature change between day and night of any planet. T e side of Mercury facing the sun bakes

in the heat. It gets 11 times hotter than Earth’s average temperature. T e side of Mercury that faces away from the sun gets very cold. Temperatures there drop hundreds of degrees below freezing. Ice may even form in some of Mercury’s craters. Mercury spins slowly, so the side facing the

sun is bathed in light for about 59 Earth days. A lot of heat builds up during that time. Yet the heat doesn’t last. Mercury has almost

no atmosphere to trap the heat. As the planet rotates, the dark side cools quickly.

Craters and wrinkles cover Mercury’s surface.

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