UPSC Prelims 2011 Q86: Science & Technology – Space Technology & Astronomy
What is the difference between asteroids and comets?
1. Asteroids are small rocky planetoids, while comets are formed of frozen gases held together by
rocky and metallic material.
2. Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found
mostly between Venus and Mercury.
3. Comets show a perceptible glowing tail, while asteroids do not.
Which of the statements given above is/are correct?
- (a) 1 and 2 only
- (b) 1 and 3 only
- (c) 3 only
- (d) 1, 2 and 3
Answer: (b) 1 and 3 only
Explanation
Asteroids vs comets: checking the three statements
Asteroids and comets are both small solar-system bodies, but they differ in composition, location, and appearance.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Asteroids are rocky planetoids; comets are frozen gases with rocky/metallic material | Correct | This accurately describes the basic compositional difference between the two |
| 2. Asteroids mostly between Jupiter and Mars; comets mostly between Venus and Mercury | Incorrect | Asteroids are indeed mostly found in the belt between Mars and Jupiter, but comets are not typically found between Venus and Mercury — they originate much farther out (Kuiper Belt, Oort Cloud) |
| 3. Comets show a glowing tail, asteroids do not | Correct | A comet's ice sublimating near the Sun creates its characteristic glowing tail; asteroids, being rocky, do not develop this feature |
Asteroids vs comets:
| Point | Asteroids | Comets |
|---|---|---|
| Composition | Rocky/metallic | Frozen gases + rock/metal |
| Typical location | Mars-Jupiter belt | Kuiper Belt / Oort Cloud (far outer solar system) |
| Tail | No tail | Glowing tail near the Sun |
Answer: (b) 1 and 3 only.
Why each option is right or wrong
- (a) Incorrect. Statement 3 (the glowing tail distinction) is also correct, so '1 and 2' wrongly includes the false location claim.
- (b) CORRECT. Statements 1 and 3 — composition difference and the tail feature — are accurate; statement 2 wrongly places comets between Venus and Mercury.
- (c) Incorrect. Statement 1 (composition difference) is also correct, so '3 only' is incomplete.
- (d) Incorrect. Statement 2's location claim for comets is false, so 'all three' cannot be correct.
Key point
Asteroids (rocky, Mars-Jupiter belt, no tail) differ from comets (frozen gases + rock/metal, from the Kuiper Belt/Oort Cloud, develop a glowing tail) — comets are NOT found between Venus and Mercury.
Remember
Asteroids: rocky, Mars-Jupiter belt, no tail. Comets: icy, from the outer solar system, develop a glowing tail near the Sun.
Common mistakes
- Placing comets' typical origin near the inner solar system (Venus-Mercury) instead of the far outer solar system.
- Not knowing the sublimation mechanism behind a comet's glowing tail.
- Missing that asteroids, being purely rocky/metallic, never develop a tail like comets do.
Exam tip
Comets come from far out (Kuiper Belt/Oort Cloud), not from near Mercury/Venus. Their glowing tail comes from ice sublimating near the Sun.
Sources
- NASA Jet Propulsion Laboratory — Small-Body Database: asteroids and comets
- NCERT Class VIII Science — Stars and the Solar System