Chapter 17: Stars and the Solar System Class 8 Notes

Solar System Class 8 Notes Pdf


Inner Planets: The four planets Mercury Venus Earth Mars are called Inner Planets.

These are also called terrestrial planets which means earth like planets.


Outer Planets: Jupiter, Saturn Uranus, and Neptune are called outer planets.

These planets are also called Jovian planets which means Jupiter like planets or Gas giants.


  • It is the smallest planet of our solar system
  • It is the fastest revolving planet around the. sun but rotation is slower than earth.
  • not the hottest planet although closest to the sun.
  • has a thin atmosphere, so trapping of heat is lesser.
  • Mercury is highly dense and 2nd in list after earth.
  • Mercury has no moon


  • 2nd planet from the sun
  • brightest planet
  • has a thick and toxic atmosphere of CO2 which reflects a lot of sunlight
  • hottest planet due to the presence of yellowish sulfuric acid cloud which absorbs a lot of heat
  • it is called earth’s twin because of its size and density.
  • takes 243 days to complete one rotation, makes day longer than year.
  • it rotates in clockwise direction
  • has a surface temperature of 475 degree Celsius.
  • No. of Moons: No Moon


  • only planet that supports life
  • fifth largest planet on the earth
  • No. of Moons: 1
  • Rotation time: 23 hrs 56 mins
  • Revolution: 365.24 days


  • fourth planet from the sun
  • is called reddish planet because of reddish iron oxide on its surface.
  • No. of Moons: 2 (Phobos, Deimos)
  • It has a very thin atmosphere made of carbon dioxide, nitrogen, and argon.


  • it is fifth planet from the sun
  • Largest planet of the solar system
  • Jupiter’s atmosphere is made up mostly of hydrogen (H2) and helium (He).
  • the Great Red Spot is a gigantic storm and it is about twice the size of Earth
  • Jupiter doesn’t support life but some of its moons might support as they have oceans beneath their crust.
  • NASA’s Juno orbiter – is currently exploring this gas giant.
  • No. Of Moons- 53+26=79


  • 6th planet from the sun
  • 2nd largest planet of solar system
  • like Jupiter, it is also made mostly of hydrogen and helium.
  • a unique planet as it has thousands of rings made up of ice and rock chunks
  • No. Of Moons- 53+29=82


  • Discovered in 1781 by William Herschel
  • third largest planet of the solar system
  • Like Venus, Uranus also rotate clockwise
  • First planet to be discovered with the help of telescope
  • Uranus is called ice giant, as most of its mass is a hot dense fluid of icy materials- water, methane and ammonia.
  • Uranus has 13 known rings.
  • Has a atmosphere of hydrogen and helium and also methane
  • Methane makes Uranus blue
  • Most remarkable feature: highly tilted rotational axis
  • Voyager 2 is the only spacecraft to fly by Uranus
  • No. Of Moons- 27


  • It was discovered in 1846 by Urbain Le Verrier, John Couch Adams, and Johann Galle.
  • spacecraft visited Neptune is Voyager 2
  • Neptune has a thick, windy atmosphere.
  • It has six rings but hardly visible
  • No. Of Moons- 14

Read Also: Chapter 4 – Materials: Metals And Non-Metals Revision Notes

Asteroids or Planetoids

Asteroids or Planetoids are rocky, airless remnants left over from the early formation of our solar system.

  • Asteroids, sometimes called minor planets
  • Asteroids – planetoids – were first discovered in 1801
  • The size is from few meters to hundreds of kilometers in width
  • These are generally found between mars and Jupiter forming a belt called Asteroid belt.

Kuiper Belt

In the year 1951, Gerard Kuiper predicted belt of icy objects beyond Neptune.

  • It was discovered by David Jewett and Jane Liu in 1992.
  • It is a collection of icy objects outside the orbit of Neptune called Kuiper Belt objects.
  • It ranges from 30 AU to 50 AU
  • Famous KBOS are dwarf planets like Makemake, Haumea, Eris and Pluto


  • These are lumps or small pieces of rock and iron that orbit the sun.
  • On coming closer to a planet (earth), gravitation pulls them in.


  • Meteoroids with Bright streaks of light in the sky
  • meteoroids Start burning on entering earth’s surface due to friction
  • Also known as Shooting Stars, but they are not stars.


  • Meteoroids that fall on a planet (earth) or moon


  • cosmic snowballs of frozen gases, rock, and dust moving around the sun in elongated orbit.
  • glowing gases and tail form tail of the comet
  • Halley comet appears after 76 years, last appeared in 1986


A satellite is an object in space that orbits or circles around a bigger object. There are two kinds of satellites: natural (such as the moon orbiting the Earth) or artificial (such as the International Space Station orbiting the Earth).

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