Our Solar System contains several types of object that orbit the Sun. Describe the differences between asteroids, comets, and planets in terms of their orbit shapes, the material they are made from, and where they are found in the Solar System.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Planets orbit the Sun in nearly circular (low‑eccentricity) orbits.
Comets travel in highly elongated (high‑eccentricity) orbits.
Asteroids are rocky or metallic bodies.
Comets are composed of ice, dust and some rock.
Asteroids are mainly found in the asteroid belt between Mars and Jupiter, whereas comets originate in the outer Solar System and spend most of their time far from the Sun, only approaching the Sun on their perihelion passages.
Comets travel in highly elongated (high‑eccentricity) orbits.
Asteroids are rocky or metallic bodies.
Comets are composed of ice, dust and some rock.
Asteroids are mainly found in the asteroid belt between Mars and Jupiter, whereas comets originate in the outer Solar System and spend most of their time far from the Sun, only approaching the Sun on their perihelion passages.
Examiner tips
- Use the exact terms ‘nearly circular’ and ‘highly elongated’ to match the mark scheme.
- Mention the composition of each type (rock/metal, ice/dust) and their typical locations.
- Keep the answer concise – one sentence per point – to fit the 5‑mark limit.
Common mistakes
- Confusing the orbit shapes of asteroids and comets; both are elliptical but only comets are highly elongated.
- Mixing up the locations – placing comets in the asteroid belt or planets in the Kuiper belt.
- Using vague terms like ‘small’ or ‘big’ instead of the specific materials and orbital characteristics.
Mark scheme (5 marks)
- Planets have nearly circular (elliptical) orbits / comets have highly elongated (elliptical) orbits
- Asteroids are made of rock and/or metal
- Comets are made of ice and dust / rock and ice
- Asteroids are mainly found in the asteroid belt between Mars and Jupiter
- Comets travel from the outer Solar System towards the Sun and back / spend most of their time far from the Sun
Key terms in this question
asteroid · comet · planet · orbit
Related
- All WJEC A-Level Physics (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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