- Group of celestial bodies like Sun, eight planets, satellites, asteroids, comets, etc.
- Discoverer (Heliocentric concept): Nicolaus Copernicus
- Origin: 4.5 billion years ago
4.5 Bn yrs
Origin of Solar System
- Proposed by Immanuel Kant, 1755 AD
- Modified in 1796 by Laplace
- A collapsing gas-and-dust nebula formed the Solar System; hydrogen fusion began in the Sun’s core. Hydrogen is about 73% of the Sun by mass.
⚡ Quick Recall
Nebular Theory: Kant (1755) → Modified by Laplace (1796)
| Key Fact | Value / Details |
|---|
| Location | Centre of solar system |
| Age | ~4.6 billion years |
| Diameter | About 13,91,400 km (about 109 Earth diameters) |
| Volume | 13 lakh times of Earth |
| Mass | About 3,33,000 Earth masses |
| Distance from Earth | 14.96 crore km |
| Chemical composition | Hydrogen ~73%, helium ~25%, heavier elements ~2% (photospheric mass) |
| Core temperature | 15 million°C (1.5×10⁷°C) |
| Period of rotation | About 25 days at the equator; ~36 days near the poles (differential rotation) |
| Source of Energy | Nuclear Fusion |
| Layer | Key Details |
|---|
| Corona (Upper layer of the Sun) | Hot outer atmosphere: up to about 2 million°C |
| Core (Central part) | Site of Thermo-Nuclear Fusion |
| Photosphere | Sphere of Light • Bright part / Radiant |
- Nearest star to solar system: Proxima Centauri
- Speed of light: 3×10⁸ m/s; Sun-to-Earth light travel: about 8 minutes 20 seconds
- Aditya-L1: India’s first solar mission; observes from a halo orbit around Sun–Earth L1.
- Midnight Sun: Arctic region • Country of Midnight Sun – Norway
⚠ Exam Trap
Aditya-L1 is positioned at
Lagrange Point L1 (not L5) — a commonly twisted detail in MCQs.
- Total Number – 8: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
- Shine with sunlight
- Revolve around the Sun
Terrestrial / Inner Planets
Mercury, Venus, Earth, Mars
- Formed from rocky (solid) substances
- Solid Surface
- Few satellites
- Absence of rings
- Comparatively smaller
Jovian / Outer / Jupiter-like Planets
Jupiter, Saturn, Uranus, Neptune
- Jupiter/Saturn: gas giants; Uranus/Neptune: ice giants
- More satellites
- Presence of rings
- Comparatively larger
⚡ Quick Recall
Most planets
rotate West→East;
Venus and Uranus rotate retrograde. Rotation and orbital revolution are different motions.
1 Mercury
- Nearest to the Sun • Very hot planet
- No satellite; water ice exists in permanently shadowed polar craters.
- Smallest planet • Highest orbital speed (fastest planet)
- Large day–night surface-temperature range: about 610°C (430°C to −180°C)
2 Venus
- Morning-Star name: Lucifer; Venus makes the closest minimum approach to Earth, while Mercury is closest on average over time.
- Brightest and hottest planet; mean surface temperature about 464°C
- Dense carbon-dioxide atmosphere with clouds of sulfuric-acid droplets
- Evening star or Morning star (seen in west in evening and east in morning)
- Earth's twin / Earth's sister planet (similar in density, size and diameter)
- Rotates clockwise / retrograde (East to West); orbital revolution is a different motion.
- No satellite
3 Earth
- Shape – Geoid • Fifth largest planet of the solar system
- Densest planet of the solar system
- Blue Planet (water); only planet known to support life
- Only natural satellite – Moon
- Nearest star after the Sun – Proxima Centauri
4 Mars
- Red planet (due to iron oxide, red soil)
- Axis tilt and day-night duration similar to Earth
- Second smallest planet after Mercury
- Two major satellites – Phobos and Deimos
- Largest volcano – Olympus Mons
- Olympus Mons: largest volcano and one of the tallest planetary mountains in the Solar System
- Mission – Mangalyaan
⚠ Exam Trap
Venus and Uranus are the only two planets with retrograde (East→West) rotation — Venus among the inner planets, Uranus among the outer.
5 Jupiter
- Largest planet of the solar system
- Banded colours: cloud chemistry including ammonia, ammonium hydrosulfide and sulfur/phosphorus-bearing chromophores
- Least rotation period (on its axis)
- Jupiter has a faint ring system; do not confuse it with Saturn’s prominent ice-rich rings.
- Jupiter: largest planet; its Great Red Spot is a massive storm.
- A massive storm – Great Red Spot present
- Atmosphere full of Hydrogen, Helium and other gases
- Satellites discovered by Galileo – 4: Ganymede (largest), Io, Europa, Callisto
6 Saturn
- Second largest planet • Gas giant and massive body (Hydrogen + Helium)
- Rings made of rocks and ice chunks → discovered by Galileo Galilei
- Most known moons in the July 2026 OP snapshot: Saturn, 293
- Density – less than water (can float on water)
- Pale yellow appearance: ammonia crystals and atmospheric haze
- Satellites – Titan (largest, similar to size of Mercury), Mimas, Tethys, Rhea, Phoebe, Enceladus, etc.
7 Uranus
- Discoverer – William Herschel (1781 AD)
- Third largest planet (by radius) • Fourth largest planet (by mass)
- Colour – Greenish (due to methane) • Tilted planet, known as Ice giant
- Lowest recorded minimum atmospheric temperature among planets; atmosphere mainly hydrogen and helium
- Clockwise rotation like Venus (East to West)
- Satellites: Titania (largest), Ariel, Miranda, etc.; 29 known moons in the July 2026 OP snapshot
8 Neptune
- Farthest from the sun • Ice giant
- Blue appearance: methane absorbs red light; other atmospheric effects deepen the colour.
- Fourth largest and third heaviest planet of the solar system
- Atmosphere made of Hydrogen and Helium
- Le Verrier and Adams predicted Neptune’s position; Johann Galle observed it in 1846.
- Satellites – Triton, Nereid
⚠ Exam Trap
July 2026 OP snapshot: Saturn
293 known moons; Uranus
29. These are dated counts.
| Planet | Diameter (km) | Orbital / Revolution Period | Satellites | Colour (Reason) |
|---|
| Mercury | 4,879 | 88 days | 0 | — |
| Venus | 12,104 | ~224.7 days | 0 | Bright (due to warming) |
| Earth | 12,756–12,714 | 365.26 days | 1 | Blue (due to water) |
| Mars | 6,792 | 687 days | 2 | Red (due to iron oxide) |
| Jupiter | 1,42,984 | 11.86 years | 115 (July 2026) | Banded cloud chemistry |
| Saturn | 1,20,536 | 29.5 years | 293 (July 2026) | Yellow (due to ammonia) |
| Uranus | 51,118 | 84.0 years | 29 (July 2026) | Green (due to methane) |
| Neptune | 49,528 | 165 years | 16 | Light blue (due to methane) |
By Distance from Sun
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
By Size (Diameter; Mass Order Differs)
- Jupiter
- Saturn
- Uranus
- Neptune
- Earth
- Venus
- Mars
- Mercury
By Density
- Earth
- Mercury
- Venus
- Mars
- Neptune
- Jupiter
- Uranus
- Saturn
By Revolution Period
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
By Orbital Speed (Highest to Lowest)
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
⚠ Exam Trap
Moving outward from Mercury to Neptune,
distance and orbital period increase while
orbital speed decreases. Size and mass rankings also differ between Uranus and Neptune.
| Key Fact | Details |
|---|
| Nature | Earth’s natural, non-luminous satellite; its ancient cratered surface preserves early impact history. |
| Sea of Tranquility | First step of Neil Armstrong |
| Distance from Earth | 3,84,400 km |
| Radius / Diameter | Radius – 1737.5 km • Diameter – 3475 km |
| Rotation + Revolution | Rotation and sidereal revolution: ~27.3 days; libration allows ~59% to be seen over time. |
| Moon's Gravity | 1/6th of Earth |
| Highest Mountain | Highest measured elevation: 10,786 m above mean lunar radius, far side near Engel’gardt crater |
| Moonlight to Earth | About 1.3 seconds |
| Scientific Study | Selenology |
| Mission | Chandrayaan-1, Chandrayaan-2, Chandrayaan-3 |
Comet / Tail Star
- Bodies made of stone, dust, ice and gas
- Approaching the Sun, solar heating causes volatile ices to sublimate, forming a coma and tail.
- Tail always points away from the sun
- Halley’s Comet: last perihelion 1986; next expected 2061.
Asteroids
- Big-big rocks
- Small bodies orbiting the sun between Mars and Jupiter
- First asteroid discovered – Ceres
- Visible with naked eye – 4 Vesta
- Asteroid named after Pt. Jasraj (2019)
Meteoroids, Meteors & Meteorites
- Meteoroids: debris from asteroids and comets in space
- Revolve around the sun
- Meteors: atmospheric light phenomena; many occur mainly in the mesosphere (~50–85 km).
- Meteor → Shooting star
- Meteorite – those which fall on Earth without burning completely
- Meteor showers / sighting month – December, January
- Lyrid Meteor shower – April
⚡ Quick Recall
Asteroid Belt lies between
Mars and Jupiter · Kuiper Belt lies
beyond Neptune.