Year 7 Science · Unit 4 · Lesson 17
Extension · Apply Worksheet
Learning Goals
Extension · optional
Asteroids, comets, meteors and the moons of other planets are not in Science 7–10 at all, so nothing on this sheet is assessed in Year 7. Our own Moon is: its phases and eclipses are assessed, and the core lessons of this unit cover them.
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. Mars has two tiny, lumpy moons called Phobos and Deimos.
Correct it:
2. Titan, Saturn’s largest moon, has lakes of liquid made of cold methane, not water.
Correct it:
3. Most asteroids are found between the orbits of Earth and Mars.
Correct it:
4. A comet’s glowing tail is smoke from rock burning on its surface.
Correct it:
5. Ganymede, a moon of Jupiter, is larger than the planet Mercury.
Correct it:
1. Why is a comet sometimes called a “dirty snowball”?
Scenario: a comet loops the Sun
A comet races in towards the Sun. The Sun’s heat turns its ice straight into gas, and gas and dust stream off to form a long glowing tail. The comet loops around the Sun and heads back out into deep space.
2. Draw the Sun and the comet’s looping path. Mark the comet at A, on its way in, and at B, on its way out. Draw its tail at A and at B, and add an arrow at each to show which way the comet is moving.
3. A friend draws the comet at B with its tail trailing behind it, like smoke behind a car. Explain what is wrong with the drawing and why.
4. A space probe flies from Mars towards Jupiter, straight through the asteroid belt, and hits nothing. There are millions of asteroids in the belt. Explain how the probe got through safely.
Read the data: Halley’s Comet
Scenario: a comet that keeps coming back
Halley’s Comet follows a long, stretched orbit and returns close to the Sun again and again. Table 1 lists three of its recorded returns.
| Return | Year |
|---|---|
| First in the table | 1835 |
| Second | 1910 |
| Third | 1986 |
Source: standard recorded dates (the lesson gives 1986 and “about once every 76 years”).
5. Work out the number of years between each pair of returns in Table 1.
Gaps years
6. Predict the year of the comet’s next return. Explain how you used the data, and why your answer is “about” rather than exact.
7. Long ago, a large lump of iron from space fell towards the Tanami Desert in Western Australia. Describe its journey from space to the ground and what it left behind.
True or false
1. True. 2. True. 3. False: most are between the orbits of Mars and Jupiter. 4. False: the tail is gas and dust given off as the Sun’s heat turns the comet’s ice straight into gas. 5. True.
Question 1
It is made of ice and frozen gases mixed with dust and rock. [1 mark]
Question 2
Sun, looping path and A and B marked. At A the tail points away from the Sun, behind the comet (1). At B the tail still points away from the Sun, so it is ahead of the comet (1). Arrows show motion towards the Sun at A and away at B (1). [3 marks]
Question 3
The tail does not trail behind; it is pushed by sunlight and particles streaming from the Sun (1), so it always points away from the Sun and at B it leads the comet (1). [2 marks]
Question 4
The belt is mostly empty space (1), so the asteroids are usually very far apart (1). [2 marks]
Read the data: Question 5
1910 − 1835 = 75 years (1); 1986 − 1910 = 76 years (1). [2 marks]
Question 6
About 2061–2062 (1): add the usual gap of about 75–76 years to 1986 (1). The gaps are not all the same, so the return can only be predicted approximately from this data (1). (Astronomers predict 2061.) [3 marks]
Question 7
Marking guide: 1 enters the atmosphere at very high speed; 1 heats up and burns, making a streak of light: a meteor; 1 most pieces burn up completely, but this lump was big enough to survive; 1 the piece that lands is a meteorite; 1 it slammed into the ground and blasted out a bowl-shaped crater; 1 Wolfe Creek Crater (Kandimalal, Djaru name), about 880 m across, one of the best-preserved on Earth. [6 marks]
Model answer: The lump hit the atmosphere very fast, heated up and glowed as a meteor. Small pieces burn up completely, but this one was big enough to survive and land, so it became a meteorite. It slammed into the desert and blasted out a bowl-shaped crater: Wolfe Creek Crater, which the Djaru People call Kandimalal, about 880 m across.
Common error: drawing the tail streaming behind the comet on its way out.