Our Solar System and where space rocks live
The Sun, eight planets, their moons and millions of smaller bodies make up our Solar System. In this lesson you will find out where the asteroids and comets are.
- Name the eight planets in order from the Sun.
- Describe where asteroids and comets are found.
- Compare the sizes of a planet and an asteroid using large numbers.
Links to: Year 5 science, Earth and space: the planets move around the Sun; maths: numbers up to 10,000,000 and division.
The Sun and its planets
The Sun is a star at the centre of our Solar System. Its gravity holds everything else in place. Eight planets travel around it on paths called orbits. In order from the Sun they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The four planets nearest the Sun are small and rocky. The four further out are giants made mostly of gas or ice. Earth takes one year to travel once around the Sun.
The asteroid belt
Between Mars and Jupiter is a wide ring of rocky and metal objects called the asteroid belt. Asteroids are far smaller than planets. The biggest, Ceres, is about 940 kilometres across, while many are no bigger than a house.
Even though there are millions of asteroids, the belt is mostly empty space. The asteroids are so far apart that spacecraft have flown through the belt without hitting anything.
Jupiter's strong gravity stirs up the asteroids. Over millions of years it nudges some of them, and pieces broken off in collisions, onto paths that cross Earth's orbit. That is how many meteorites start their journey to us.
Comets far away
Much further out, beyond Neptune, are billions of icy bodies. When one of them swings close to the Sun it warms up, and gas and dust stream off it to make a glowing tail. We call it a comet.
Comets leave trails of dust along their orbits. In lesson 11 you will find out what happens when Earth passes through one of those trails.
How many Ceres would fit across Earth?
Earth is about 12,700 km across. Ceres is about 940 km across. Roughly how many Ceres would fit side by side across Earth?
- We need to find how many lots of 940 fit into 12,700, so we divide: 12,700 ÷ 940.
- Round to make it easier: 940 is close to 1,000, and 12,700 ÷ 1,000 = 12.7. Because 940 is a little less than 1,000, the real answer will be a little more than 12.7.
- Check by multiplying: 940 × 13 = 12,220, which is just under 12,700. 940 × 14 = 13,160, which is too much.
Answer: About 13 Ceres would fit across Earth, and Ceres is the largest asteroid of all.
Make a planet line. Use a long strip of paper or the school field. Mark the Sun at one end, then use this guide (1 step is about 1 metre): Mercury 1, Venus 2, Earth 3, Mars 4, asteroid belt 6 to 8, Jupiter 13, Saturn 24, Uranus 49, Neptune 77. Stand at the asteroid belt and look at how far you are from Earth.
Quiz
5 questions. Choose an answer to see whether you are right and why. Finish the quiz to complete the lesson.
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Question 1What holds the planets and asteroids in their orbits?
The Sun's gravity pulls on everything in the Solar System and keeps the planets and asteroids travelling around it.
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Question 2Which planet comes straight after Mars, going outwards from the Sun?
The order is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The asteroid belt lies between Mars and Jupiter.
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Question 3What is Ceres?
Ceres is the biggest object in the asteroid belt. It is large enough to be round and is also called a dwarf planet.
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Question 4Why can spacecraft fly through the asteroid belt safely?
There are millions of asteroids, but the belt is so huge that the space between them is enormous.
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Question 5Earth is about 12,700 km across and Ceres is about 940 km across. About how many Ceres fit across Earth?
12,700 ÷ 940 is about 13.5, and 13 Ceres side by side measure about 12,220 km.