Our Solar System



  • Solar system originted from a nebula which started collapsing and core formation about 5 to 5.6 billion years ago.
  • All planets were formed about 4.6 billion years ago.
  • Our solar system consists of the sun (the star), 8 planets, many moons, millions of smaller bodies like asteroids and comets and huge quantity of dust-grains and gases.
  • Out of the eight planets, mercury, venus, earth and mars are called as the inner planets as they lie between the sun and the belt of asteroids .
  • They are also called Terrestrial, meaning earth-like as they are made up of rock and metals.
  • They have relatively high densities.
  • Other four planets are called the outer planets and also called Jovian or Gas Giant planets.
  • Jovian means Jupiter-like.
  • NASA’s Voyager-1 and Voyager-2 only two spacecrafts so far to leave our solar system.


space mission history



  • Sun is a G2 star and revolves around the galactic core.
  • It completes one revolution in 230 million years which is known as 1 Cosmic Year.
  • It comprises about 99.86% of the mass of our Solar System.
  • Sun is composed primarily of the chemical elements hydrogen and helium.
  • Hydrogen converted into helium and energy has been produced by nuclear fusion.
  • Sunlight at the top of Earth’s atmosphere is composed
    • 50% infrared light
    • 40% visible light
    • 10% ultraviolet light
  • Apparent rotational period of the Sun at its equator is about 28 days
  • Average luminance of the Sun is about 1.88 Giga candela /m2, but as viewed through Earth’s atmosphere, this is lowered to about 1.44 Gcd/m2.


Structure of the Sun


Structure of the Sun


  • Innermost 20-25% of the Sun’s radius, where temperature and pressure are sufficient for nuclear fusion
  • Hydrogen fuses into helium. The fusion process releases energy


Radiative Zone

  • Between about 20-25% of the radius, and 70% of the radius, there is a radiative zone



  • the boundary region between the radiative and convective zones.


Convective Zone

  • Between about 70% of the Sun’s radius and a point close to the visible surface.



  • the deepest part of the Sun which we can directly observe with visible light.
  • Photosphere has a temperature of around 6000°C
  • Sunspots appears in photosphere



  • A gaseous ‘halo’ surrounding the Sun, comprising
    • Chromosphere – Plages occurs here, it is rosy red color, apparent during eclipses
    • Solar transition region
    • Corona – Outermost part of sun, Solar Flares occurs here
    • Heliosphere – is the bubble-like region of space dominated by the Sun, which extends far beyond the orbit of Pluto.



  • Sunspots are darker, cooler regions on the bright, hot photosphere.
  • Whilst the photosphere has a temperature of around 6000°C, sunspots are between 3000°C and 4000°C.
  • They move across the surface of the Sun.
  • Sunspots number varies according to the 11-year solar cycle.
  • Galileo studied sunspots in 1610.


Solar Flares

  • Those are sudden variations in the brightness of a surface region of the Sun.
  • Magnetic energy builds up in the solar atmosphere, above active regions
  • Solar flares also pose a radiation hazard to astronauts in the International Space Station.


Solar Wind

  • Solar wind is a stream of energized, charged particles, primarily electrons and protons.
  • It flows outward from the Sun, through the solar system.
  • Speed of solar winds as high as 900 km/s and at a temperature of 1 million 0C.
  • It is made of plasma.
  • Solar winds affect the magnetic field of the Earth.



Planets of our Solar System


Difference between Terrestrial & Jovian planets

  • The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles.
  • Jovian planets were formed at quite a distant location.
  • The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets.
  • The solar winds were not all that intense to cause similar removal of gases from the Jovian planets.
  • The terrestrial planets are smaller and their lower gravity could not hold the escaping gases




Planets of our Solar System


  • Mercury is the closest planet to the Sun.
  • It is also the smallest planet in our Solar System.
  • Mercury is made mainly of iron.
  • After Earth it is the second most dense planet in our Solar System.
  • It has no moon of its own.
  • Big differences in day-time ( 427 °C) and night-time ( -173 °C) temperatures
  • Orbital period of Mercury is 88 days.



  • Venus is the 2nd planet from the Sun.
  • Orbital period of Venus is 224.7 days.
  • It has the longest rotation period 243 days
  • Venus rotates in the opposite direction to most other planets.
  • The Sun would rise in the west and set in the east.
  • It does not have any natural satellites
  • Venus is the 2ndbrightest natural object in the night sky after the Moon.
  • It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% CO2.
  • Venus is the hottest planet in our Solar System, with a mean surface temperature of 462 °C.
  • It was the 1st planet to have its motions plotted across the sky as early as the 2nd millennium BC.
  • Venus is the closest planet to Earth.
  • It is similar to Earth in size and mass, and is often described as Earth’s “sister” or “twin”
  • Venus was the first planet visited by a spacecraft (Mariner 2 in 1962, by NASA).




  • Mars is the 4th from Sun and the 2nd smallest planet.
  • Olympus Mons is the largest volcano, the tallest planetary mountain with height of 25km.
  • Mars has two moons, Phobos and Deimos,  may be captured asteroids.
  • Mars trojans are a group of objects that share the orbit of the planet Mars around the Sun
  • It having about 15% of Earth’s volume and 11% of Earth’s mass, resulting in about 38% of Earth’s surface gravity.
  • Mars lost its magnetosphere 4 billion years ago.
  • Atmosphere of Mars consists of about 96% CO2.
  • Mars has polar ice caps.
  • Mariner 9 was 1st successfully mission, 1971, landed a spacecraft on Mars.
  • Mangalyaan, is a space probe orbiting Mars, was launched on 5 November 2013 by ISRO



  • Jupiter is the 5th from Sun the largest planet.
  • Its volume is that of about 1,321 Earths.
  • Jupiter and Saturn are gas giants; the other two giant planets, Uranus and Neptune, are ice giants.
  • It has 79 known moons.
  • Jupiter’s four largest moons Io, Europa, Ganymede and Callisto.
  • Those were first observed by Galileo Galilei in 1610 using telescope.
  • Io is the most volcanically active body in our solar system.
  • Ganymede is the largest moon in the solar system.
  • Jupiter has the same ingredients as a star, but it did not grow massive enough to ignite.
  • It is composed of hydrogen and helium.
  • Jupiter still radiates more heat than it receives from the Sun.
  • It has the largest planetary atmosphere in our Solar System, spanning over 5,000 km in altitude.
  • Jupiter has the shortest day in our  solar system, only about 10 hours.
  • It makes a complete orbit around the Sun in about 12 Earth years.
  • Its magnetic field is 16 to 54 times as powerful as that of the Earth, causes some of the solar system’s most spectacular aurorae at the planet’s poles.
  • 1st spacecraft to visit Jupiter was Pioneer-10 in 1973.


Cassini Mission to Saturn
Cassini Mission


  • Saturn is the 6th fromthe Sun and 2nd largest planet.
  • It has rings, that was first observed in 1610 by the astronomer Galileo Galilei
  • Saturn is made mostly of hydrogen and helium.
  • One day on Saturn takes only 10.7 hours.
  • Saturn makes a complete orbit around the Sun in about 29.4 Earth years.
  • Its axis is tilted by 26.73 degrees.
  • It is the only planet in our solar system whose average density is less than water.
  • Saturn’s rings are thought to be pieces of comets, asteroids or shattered moons that broke up before they reached the planet
  • It has 82 moons, in which 53 moons are confirmed and named.
  • Largest moon of Saturn is Titan.
  • Pioneer 11 launched in 1973 was the 1st mission to Saturn by NASA.
  • Cassini mission, was the most important launched in 2004 by NASA.



  • Uranus is the 7th from Sun and 3rd largest.
  • It is very cold and windy planet
  • The ice giant is surrounded by 13 faint rings and 27 small moons as it rotates at a nearly 90-degree angle from the plane of its orbit.
  • This unique tilt makes Uranus appear to spin on its side, orbiting the Sun like a rolling ball.
  • Uranus is the first planet found with the aid of a telescope.
  • It was discovered in 1781 by astronomer William Herschel.
  • Uranus is 4 times wider than Earth.
  • One day on Uranus takes about 17 hours.
  • It makes a complete orbit around the Sun in 84 Earth years
  • It is the only planet equator is nearly at a right angle to its orbit, with a tilt of 97.77 degrees
  • Uranus also rotate in opposite direction like Venus, from east to west
  • It has 27 known moons, being named for characters from the works of William Shakespeare and Alexander Pope
  • Uranus has two sets of rings.


our solar system


  • Neptune is the 8th and most distant planet in our solar system.
  • It is 30 astronomical units away from the Sun
  • Neptune is the only planet in our solar system not visible to the naked eye
  • Johann Galle discovered the planet in 1846.
  • It is about four times wider than Earth
  • One day on Neptune takes about 16 hours
  • It makes a complete orbit around the Sun in 165 Earth years
  • Of the giant planets, Neptune is the densest
  • Its atmosphere is made up mostly of hydrogen and helium with just a little bit of methane
  • Neptune is a vivid, brighter blue colored planet.
  • It has 13 known moons, largest is Triton.




Dwarf Planets

  • It is a planetary-mass object that is neither a true planet nor a natural satellite
  • That is, it is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibriums shape.
  • The term dwarf planet was adopted in 2006.
  • As of July 2008 the International Astronomical Union (IAU) recognizes five dwarf planets
    1. Ceres – 1801
    2. Pluto – 1930
    3. Haumea – 2004
    4. Makemake – 2005
    5. Eris  – 2005




Asteroid Belt

  • Asteroid Belt is a circumstellar disc in the Solar System.
  • It is located between Mars and Jupiter.
  • Asteroid Belt is occupied by numerous irregularly shaped bodies called asteroids or minor planets.
  • Four largest asteroids
    • Ceres
    • Vesta
    • Pallas
    • Hygiea
  • Ceres, the asteroid belt’s only dwarf plane.




Kuiper Belt

  • Kuiper Belt Objects (KBOs) first time came to light in 1992.
  • It is approximately 50 AU from the Sun.
  • Kuiper Belt is 20 times as wide and 20 to 200 times as massive then asteroid belt.
  • It is the home to 3 recognized dwarf planets
    • Pluto
    • Haumea
    • Makemake




Oort Cloud

  • Oort Cloud is believed to be a thick bubble of icy debris that surrounds our solar system
  • It exists between 5,000 and 100,000 astronomical units from sun.
  • Oort Cloud is too far to be seen with current telescopes, so it hasn’t been directly seen or discovered
  • Scientists’ best guess about where long-period comets come from this region.





  • Little chunks of rock and debris in space are called meteoroids.
  • Meteorite size can about be 1 to 5 meter.
  • They become meteors or shooting stars, when they fall through a planet’s atmosphere.
  • It leaves a bright trail as they are heated to incandescence by the friction of the atmosphere.
  • Several times a year, Earth passes through a trail of debris creating meteor showers.
  • Any of these debris that survive the journey and hit the ground are called meteorites.





  • Comets are icy small Solar System body.
  • When passing close to the Sun, warms and begins to release gases, a process called outgassing.
  • This produces a visible atmosphere or coma, and sometimes also a tail.
  • Coma may be up to 15 times the Earth’s diameter, while the tail may stretch one astronomical unit.
  • Comets usually have highly eccentric elliptical orbits.
  • They have a wide range of orbital periods, ranging from several years to several millions of years.
  • Short-period comets originate in the Kuiper belt.
  • Long-period comets are thought to originate in the Oort cloud.


en English

You cannot copy content of this page

Mock Tests