Planets – Complete Notes for Competitive Examinations

(SSC • JKSSB • UPSC • JKPSC • Railway • CUET • School Exams)

What is a Planet?

A planet is a celestial body that:

1. Revolves around the Sun in a fixed orbit.

2. Has enough gravity to become nearly spherical.

3. Has cleared the neighborhood around its orbit.

Important Points

Total recognized planets in our Solar System = 8

Pluto was declared a Dwarf Planet in 2006
All planets revolve around the Sun in elliptical orbits
The study of planets is called Planetology

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Classification of Planets

1. Inner Planets (Terrestrial Planets)

Also called Rocky Planets

Planets:

Mercury

Venus
Earth
Mars

Characteristics

✔ Small in size
✔ Rocky surface
✔ Higher density
✔ Few or no moons
✔ Located before asteroid belt

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2. Outer Planets (Jovian/Giant Planets)

Planets:

Jupiter

Saturn
Uranus
Neptune

Characteristics

✔ Large size
✔ Mostly gas/ice
✔ Lower density
✔ Many moons
✔ Rings present

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1. Mercury

Important Facts

Closest planet to Sun

Smallest planet
No atmosphere (very thin exosphere)
No moons
Fastest revolution around Sun

Time

Rotation → 59 Earth days

Revolution → 88 Earth days

Temperature

Day: ~430°C

Night: ~–180°C

Missions

Mariner 10

MESSENGER
BepiColombo

Exam Facts

Smallest planet

No natural satellite

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2. Venus

Important Facts

Second planet from Sun

Hottest planet
Called Earth’s Twin
Rotates opposite direction (Retrograde rotation)

Atmosphere

Mainly Carbon Dioxide

Moons

None

Temperature

≈ 465°C

Missions

Magellan

Akatsuki

Exam Facts

• Brightest planet

• Morning Star / Evening Star

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3. Earth

Important Facts

Third planet

Only known planet supporting life

Surface:

• 71% Water

• 29% Land

Moon

• 1 Moon

Atmosphere

• Nitrogen (78%)

• Oxygen (21%)

Missions

• Apollo 11

• Chandrayaan-3

Exam Facts

• Densest planet

• Blue Planet

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4. Mars

Important Facts

• Fourth planet

• Called Red Planet

• Largest volcano:

  • Olympus Mons

• Evidence of ancient water

Moons

• Phobos

• Deimos

Missions

• Mars Orbiter Mission

• Perseverance Rover

• Curiosity Rover

Exam Facts

• Most explored planet after Earth

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5. Jupiter

Important Facts

• Largest planet

• Gas Giant

• Great Red Spot = Giant storm

Moons

• More than 90 known moons

Major:

• Io

• Europa

• Ganymede

• Callisto

Missions

• Juno

• Galileo

Exam Facts

• Shortest day (~10 hrs)

• Ganymede = Largest moon

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6. Saturn

Important Facts

• Famous for rings

• Second largest planet

Moons

• More than 140 known moons

Important:

• Titan

• Enceladus

Missions

• Cassini–Huygens

Exam Facts

• Lowest density

• Could float in water (theoretical comparison)

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7. Uranus

Important Facts

• Ice Giant

• Rotates on its side

Moons

• 27 known moons

Missions

• Voyager 2

Exam Facts

• Coldest atmosphere

• Blue-green due to methane

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8. Neptune

Important Facts

• Farthest planet

• Strongest winds

Moons

• 16 known moons

Major:

• Triton

Missions

• Voyager 2

Exam Facts

• Deep blue color

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Important Planet Comparison

Planet	Position	Moons	Special Name
Mercury	1	0	Smallest
Venus	2	0	Hottest
Earth	3	1	Blue Planet
Mars	4	2	Red Planet
Jupiter	5	90+	Largest
Saturn	6	140+	Ring Planet
Uranus	7	27	Tilted Planet
Neptune	8	16	Farthest

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Most Important One-Liners for Exams

1. Largest planet → Jupiter

2. Smallest planet → Mercury

3. Hottest planet → Venus

4. Blue planet → Earth

5. Red planet → Mars

6. Planet with rings → Saturn

7. Earth’s twin → Venus

8. Largest moon → Ganymede

9. Planet with life → Earth

10. Coldest planet → Uranus

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MCQ Questions

Q1. Which is the smallest planet?

A. Venus
B. Earth
C. Mercury ✅
D. Mars

Q2. Which planet is called Red Planet?

A. Mars ✅
B. Venus
C. Jupiter
D. Neptune

Q3. Which planet has rings?

A. Saturn ✅
B. Mercury
C. Earth
D. Mars

Q4. Largest moon belongs to which planet?

A. Jupiter ✅
B. Earth
C. Mars
D. Venus

Q5. Which planet rotates in opposite direction?

A. Venus ✅
B. Mercury
C. Jupiter
D. Earth

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Statement Type Questions

Q1. Consider the statements:

1. Mercury is the smallest planet.

2. Venus has one moon.

Choose correct answer:

A. Only 1 correct ✅
B. Only 2 correct
C. Both
D. Neither

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Q2. Consider:

1. Jupiter is a gas giant.

2. Saturn is famous for rings.

Answer:
Both statements are correct ✅

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Q3. Consider:

1. Earth is the third planet.

2. Mars has one moon.

Answer:
Only Statement 1 is correct ✅

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Memory Trick

Inner Planets:
M V E M → My Very Educated Mother

Outer Planets:
J S U N → Just Study Until Night