Year 7 Science · Unit 4 · Lesson 17
Extension · Master 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 in the core lessons of this unit.
1. Io, Europa, Ganymede and Callisto are called the Galilean moons. Which planet do they orbit, and why are they given that name?
Odd one out
Each row has a rule. Circle the one item that does not fit the rule, then say why.
| Rule | Group | Odd one out, and why |
|---|---|---|
| A moon of Jupiter | Io · Europa · Titan · Callisto | |
| A natural satellite of a planet | Phobos · Ganymede · Itokawa · Deimos | |
| True of a comet’s tail | made of gas and dust · points away from the Sun · can stretch for millions of km · always trails behind the comet |
Compare the three
Write one short, correct fact in each empty box.
| Body | What it is made of | Where it is found, or what it orbits |
|---|---|---|
| Moon | ||
| Asteroid | ||
| Comet |
2. In 2010, grains of the asteroid Itokawa, collected by Japan’s Hayabusa spacecraft, parachuted down at Woomera in South Australia. Explain why samples like these can tell scientists how the Solar System formed.
Read the data: counting moons
Scenario: do bigger planets have more moons?
Mia thinks: “The bigger the planet, the more moons it has.” She finds the data in Table 1 to test her idea.
| Planet | Width compared with Earth (Earth = 1) | Known moons |
|---|---|---|
| Mercury | 0.4 | 0 |
| Venus | 0.95 | 0 |
| Earth | 1 | 1 |
| Mars | 0.5 | 2 |
| Jupiter | 11 | about 95 |
| Saturn | 9 | about 146 |
Source: moons of Mercury to Mars from the lesson. Widths are rounded standard values; the Jupiter and Saturn moon counts are the totals announced in 2023 (the counts keep rising as small moons are found).
3. How does the number of moons change from the four worlds nearest the Sun to the two giants in Table 1?
4. Does Table 1 fully support Mia’s idea? Use two pairs of planets from the table as evidence.
5. A student writes: “Moons, asteroids and comets are basically the same thing: just rocks floating in space.” Evaluate this claim.
Question 1
Jupiter (1). Galileo first spotted them through a telescope in 1610 (1). [2 marks]
Odd one out
1 each: Titan (Saturn’s moon); Itokawa (an asteroid); “always trails behind” (it points away from the Sun, so on the way out it leads). [3 marks]
Compare the three
Moon: rock or ice (some rocky and cratered, some icy); orbits a planet. Asteroid: rock and metal; mostly in the belt between Mars and Jupiter. Comet: ice, frozen gases, dust and rock; from the cold outer edges, on a long stretched orbit of the Sun. Six boxes = 3; four or five = 2; two or three = 1. [3 marks]
Question 2
Asteroids are rocky leftovers from when the Solar System formed, about 4.6 billion years ago (1). They have barely changed since (1), so, like a time capsule, they show what the early Solar System was made of (1). [3 marks]
Read the data: Question 3
The rocky inner planets have few or no moons, 0 to 2 (1); the gas giants have far more, about 95 and 146 (1). [2 marks]
Question 4
Only partly (1). Saturn (9) is narrower than Jupiter (11) but has more moons (146 vs 95) (1). Mars (0.5) is narrower than Venus (0.95) but has 2 moons to Venus’s 0 (or Mars and Earth: 0.5 vs 1, but 2 moons to 1) (1). [3 marks]
Question 5
Marking guide: 1 judgement: mostly wrong (all are smaller bodies, and some are rocky); 1 moons orbit planets; asteroids and comets orbit the Sun; 1 asteroids are rock and metal, mostly in the belt between Mars and Jupiter; 1 comets are ice, frozen gases, dust and rock from the cold outer edges; 1 moons vary: rocky and cratered or icy; 1 near the Sun a comet’s ice turns to gas, forming a tail that points away from the Sun. [6 marks]
Model answer: Mostly wrong. All are smaller bodies and some are rocky, but moons orbit planets while asteroids and comets orbit the Sun. Asteroids are rock and metal, mostly between Mars and Jupiter; moons can be rocky or icy. Comets are icy, from the cold outer edges, and near the Sun their ice turns to gas, forming a tail that points away from the Sun.
Common error: saying asteroids orbit planets, like moons.