Planetary Geography

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Solar system: Sun + 8 planets + dwarf planets + asteroids + comets. Inner 4 (terrestrial: Mercury, Venus, Earth, Mars) and outer 4 (gas giants: Jupiter, Saturn, Uranus, Neptune).
Inner vs outer: Inner planets — rocky, small, fewer moons. Outer planets — gaseous, huge, many moons, ring systems.
Special bodies: Asteroid belt between Mars and Jupiter; Kuiper belt beyond Neptune; Pluto reclassified as dwarf planet in 2006.

Earth is one of eight planets orbiting the Sun. Planetary geography covers their order, classification, and key features — the kind of facts NDA likes to test as one-shot MCQs.

Structure of the Solar System

The Sun holds ~99.86% of the solar system's mass. Around it orbit 8 planets, at least 5 recognised dwarf planets (Pluto, Eris, Haumea, Makemake, Ceres), thousands of asteroids and innumerable comets.

Order of planets from Sun

Mercury → Venus → Earth → Mars → (Asteroid belt) → Jupiter → Saturn → Uranus → Neptune
Mnemonic: My Very Educated Mother Just Served Us Noodles.

Inner (Terrestrial) Planets

Planet	Note
Mercury	Smallest, closest to Sun, no atmosphere, extreme temperature swing.
Venus	Brightest planet, hottest (CO₂ greenhouse), rotates clockwise (retrograde).
Earth	Only known life-bearing planet; one natural satellite (the Moon).
Mars	"Red Planet"; iron oxide surface; two small moons (Phobos, Deimos); Olympus Mons is largest volcano in solar system.

Outer (Gas Giant) Planets

Planet	Note
Jupiter	Largest planet; Great Red Spot (storm); 95+ moons (Io, Europa, Ganymede, Callisto = "Galilean moons").
Saturn	Famous ring system; second-largest planet; Titan is largest moon (has atmosphere).
Uranus	Rotates "on its side" (axial tilt 98°); discovered 1781 by Herschel.
Neptune	Windiest planet; discovered 1846 mathematically before being observed; Triton is largest moon.

Asteroids, Comets and Dwarf Planets

Asteroid belt: Between Mars and Jupiter; ~1 million asteroids; Ceres is the largest (and a dwarf planet).
Kuiper belt: Beyond Neptune; home of Pluto, Eris, Makemake, Haumea.
Oort cloud: Theoretical sphere of icy objects far beyond Kuiper belt; source of long-period comets.
Comets: Icy bodies with elliptical orbits; develop tails when near the Sun. Famous: Halley's Comet (76-year period, last seen 1986, next 2061).
Pluto: Reclassified as a "dwarf planet" in 2006 by the IAU.

NDA PYQ Examples

Q: Which planet is known as the Red Planet?

(a) Venus (b) Mars (c) Jupiter (d) Mercury

Answer: (b) Mars — iron oxide on surface gives the reddish colour.

Q: Which is the largest planet in the solar system?

(a) Saturn (b) Earth (c) Jupiter (d) Neptune

Answer: (c) Jupiter.

Q: In which year was Pluto reclassified as a dwarf planet?

Drill Planetary Geography for NDA

NDA-pattern items on Planetary Geography with answer keys and explanations.

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Frequently Asked Questions

Why is Venus the hottest planet despite not being closest to the Sun?

Because of its thick CO₂ atmosphere causing a runaway greenhouse effect. Surface temperatures reach 470 °C — hotter than Mercury, which is closer to the Sun but has no atmosphere to trap heat.

What are the Galilean moons?

Jupiter's four largest moons — Io, Europa, Ganymede and Callisto — discovered by Galileo in 1610. Ganymede is the largest moon in the solar system.

Why is Pluto no longer a planet?

In 2006 the IAU defined a 'planet' as a body that has cleared its orbital neighbourhood. Pluto shares its orbit with many Kuiper-belt objects, so it was reclassified as a dwarf planet.

Which is the closest galaxy to the Milky Way?

Andromeda Galaxy (M31), about 2.5 million light-years away. It is on a collision course with the Milky Way — they will merge in ~4.5 billion years.

What is the difference between an asteroid and a comet?

Asteroids are rocky/metallic bodies, mostly in the belt between Mars and Jupiter. Comets are icy bodies, mostly from the Kuiper belt or Oort cloud, with elliptical orbits that bring them near the Sun (where they form a tail).