Competitive Exams: Planets

Terrestrial and Jovian Planets

Terrestrial planet are smaller in size; rocky in structure; slow rotation on the axis and have lesser satellite. Inner terrestrial planets are: Mercury, Venus, Earth, Mars.

Jovian planets are huge in size; spin very fast and have higher number of satellites. Outer or Jovian planets are: Jupiters, Saturn, Uranus, Neptune, and Pluto.

  • Earth is the densest of all the planets; Saturn has the lowest density (less than water 0.5)

  • Mercury is closest to the sun.

  • Sequence of planets'distance from the sun: Mercury< Venus< Earth< Mars< Jupiter< Saturn< Uranus< Pluto traces elongated elliptical orbit. So, from 1980 − 1999, the distance of Neptune was more than Pluto.

  • Uranus and Venus rotates retrograde (i.e.. from east to west), other planet rotates in the same way as earth (from west to east).

  • Venus is the only planet whose period of rotation (243 days) is longer than the period of revolution (225 days) around the sun.

  • Uranus is tilted at 90° so it almost rolls around the sun. Mars tilted at 23° in the same way as the earth, so experiences four seasons as earth.

  • Mercury is the hottest planet; Venus is the second hottest planet (600° C), atmosphere mainly made of C02 (90%).

  • Mars glows with reddish light because of high iron content; it has thin atmosphere (containing free oxygen at very low-level), also has frozen water at polar region. Due to these factors, Mars is considered as the first planet that will be colonised.

  • Jupiter's internal temperature of Jupiter is very high, close to starting nuclear fusion. Mainly hydrogen is present around the Jupiter.

  • Saturn is the second largest planet; it looks yellowish light (due to the presence of ammonia). Ring around Saturn is made up of dust particles, frozen ice, and frozen ammonia.

  • Uranus grows with blue light.

  • Neptune grows with the greenish blue light due to presence of methane.

  • Pluto is the coldest, darkest, and the strongest planet. It is smaller in size and does not fall in giant planet category


  • Mercury and Venus have no satellite.

  • Earth has one satellite: Moon

  • Mars has two satellite: Deimos and Phobos.

  • Jupiter has 19 satellites, one of the satellite known is Europa, containing large number of deep oceans. It contains possibility of extra-terrestrial life.

  • Saturn has 21 satellites (10 discovered by Voyage 1&2)

  • Uranus has 17 satellite (12 discovered by Voyage 1&2)

  • Neptune has 11, one of this is tital.

  • Pluto's satellite is Charon.


Minor planets of the solar system, small rocky structure, revolving around sun mostly between Mars and Jupiter. These are considered as debris of large planets existing between Mars and Jupiter as is evident from the distance between them.

Earth has long history of collision with: Comets, and asteroids.

Sedimentary rocks of 65 million years ago have high iridium content which gives evidence of collision of celestial body.

  • Miss distance: a celestial body coming closer beyond 9, 00, 000 km, may not strike earth. This is called as miss distance.


Member of the solar system, found revolving around the sun beyond the path of Pluto, generally, at outer edges of the solar system. Comets are made of pre-mordial substance from which solar system are made. Since, they are undisturbed due to far location, study of comets may give more information about evolution of earth or other planets. Comets are made up of frozen ammonia, dust particles and ice crystals and other chemicals.

  • Halley Comet: Appears after a period of 76 years.

  • Halle Bopp: One of the largest comet with 40 km diameter.

  • Comet Swift Turtle: Calculated to collide on 14 Aug 2126 AD in Australia

  • Comets making journey towards sun develop small head and long tail, due to heat only as it approaches Jupiter. Tail extending millions of kilometers in the outer space. Tail always point away from the sun. Solar wind is responsible for the formation of tails since solar winds goes away from the sun.


It is the alignment of three celestial bodies along a straight line; Viewed from one of these bodies, the other two will either be in conjunction or in opposition. An inferior planet, whose orbit lies inside that of earth, can, in reference to the sun as seen from the earth, be either in inferior conjunction or in superior conjunction; unlike a superior planet, whose orbit lies outside the earth's, and unlike the moon, it can never be in opposition to the sun as seen from the earth


  • Looks bluish white, body due to the presence of ocean and ice-caps.

  • Earth's core is mainly made up of iron and nickle; mantle is mostly solid. Outer core due to its movement gives magnetic field of earth manifested in Van-alien Radiation bell. Van-Allen Radiation belts are two concentric circles. Inner belt is more energetic and situated at 3000 km above the equator. Outer concentric circle is less energetic and found at 16000 km above the earth. Van-Allen radiation belts are formed due to concentration of solar-winds.

Important Statistics

  • Fastest Rotational Period (descending order) -Jupiter > Saturn > Neptune > Uranus > Earth > Mars > Pluto > Mercury > Venus
  • Density (Highest to Lowest) -Earth > Mercury > Venus > Mars > Neptune > Jupiter > Uranus > Saturn
  • Size (Biggest to Smallest) -Jupiter > Saturn > Uranus > Neptune > Earth > Venus > Mars > Mercury > Pluto