Solar system

Introduction to the solar system

What is the solar system?

The solar system is basically the sun at the center and all other celestial bodies like 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), their moons, asteroids, meteoroids, Dwarf planets, and comets revolving around it. This whole system is known as the solar system.

How it was formed and where we located in the universe?

According to research, it is known that our solar system was formed 4.5 billion years ago after the big bang. At that time majority of the space is covered with the H and He gas. The same way our Milkyway was full of dust and gas clouds.

formation of the solar system
Image Credit: wikipedia

In the beginning, roughly 30000 Ly away from the center of the Milkyway a giant cloud of dust and gas was formed and known as a nebula. This nebula started to contract and collapse into itself, atoms of gas & dust clouds started colliding into each other and enormous heat was produced and because of a process called nuclear fusion star was born which is known as The Sun.

Due to the gravity of the sun material around it settled into a disk form which is known as an accretion disk. This disk is made of the same material of gas and tiny grains of the dust cloud.

In this disk, dust particles started sticking together and formed a hard rocky core for the planet formation. A plethora of collisions and impacts were done in this process which become the main reason for the creation of moons and asteroids.

Two types of planets formed (Gas giants & Rocky planets)

There is a total of eight planets in the solar system, the First four (Mercury, Venus, Earth, Mars) is known as the Terrestrial planets and the last four (Jupiter, Saturn, Uranus, Neptune) is known as the Jovian planets.

The main reason behind this differentiation is solar radiation or stellar winds. At the time of formation due to solar radiation majority of gas was wiped out and the rocky core was left but the gas giants cannot able to hit up due to the distance from sun, so they retained their gaseous components and left with a small rocky core with a large amount of gas or ice.

Properties of the Terrestrial and Gas giants

Terrestrial PlanetsGas giants (Jovian Planets)
Solid surface (Rock & Metal)Surface covered with gas (H & He)
Small size and higher densityLarge size and lower density
No rings and single or two moonRings and plethora of moons

Terrestrial Planets


image credit: NASA
  • First and closest planet from the sun.
  • Distance from the sun in AU: 0.39
  • Orbital Period: 88 Days
  • Rotational Period: 59 Days
  • No. of natural satellites: 0
  • Surface temperature varies from 427 C to (-180 C)
  • Due to inner orbit from the earth, we can see phases of the mercury like our moon.
  • Rarely observable with naked eye due to sun’s glare, best time to observe the mercury is one hour before sunrise or one hour after sunset according to its visibility.


Image Credit: NASA/JPL
  • Second planet from the sun and closest planet from the Earth.
  • Distance from the sun in AU: 0.72
  • Orbital Period: 225 Days
  • Rotational Period: 243 Days
  • No. of natural satellites: 0
  • Surface temperature: 460 C
  • Due to inner orbit from the earth, we can see phases of the Venus like our moon.
  • Hottest planet in our solar system.
  • Not star but known as the “Morning star or Evening star”.
  • One of the brightest planet seen from the earth.
  • Due to higher rotational period than the orbital period, one day on the venus is larger than its one year.


Image Credit: NASA
  • We all know about it, Our beautiful home planet and third from the Sun.
  • Distance from the sun in AU: 1 (149.6 milloin km)
  • Orbital Period: 365.4 Days
  • Rotational Period: 23H:56M
  • No. of natural satellites: 1
  • Surface temperature: 60 C to (-41 C)
  • Seasons exist on the earth due to tilted position of its rotational axis.
  • Only planet in the solar system where humans live.


Image Credit: NASA
  • Fourth planet from the sun and known as the Red planet.
  • Distance from the sun in AU: 1.5
  • Orbital Period: 687 Days
  • Rotational Period: 24H:37M
  • No. of natural satellites: 2 (Phobos and Deimos)
  • Surface temperature: 20 C to (-140 C)

Gas Giants


Image Credit: NASA
  • Fifth planet from the sun and largest planet in the solar system.
  • Distance from the sun in AU: 5.2
  • Orbital Period: 11.8 Years
  • Rotational Period: 9H:50M
  • No. of natural satellites: 79 moons till 2021 (4 large moons known as “galilean moons”)
  • Surface temperature: (-145 C)
  • Jupiter can accomodate more than 1300 Earths inside it. And The Great Red Spot itself can accomodate more than 3 Earth like planets.


Image Credit: NASA
  • Sixth planet from the sun and second largest planet in the solar system.
  • Distance from the sun in AU: 9.5
  • Orbital Period: 29 Years
  • Rotational Period: 10H:14M
  • No. of natural satellites: 82 moons till 2021 (Largest moon is Titan)
  • Surface temperature: (-180 C) to (-120 C)
  • Well known for beautiful rings around it.


Image Credit: NASA
  • Seventh planet from the sun. Discovered by William Herschel in 1781.
  • Distance from the sun in AU: 19.1
  • Orbital Period: 84 Years
  • Rotational Period: 17.2 H
  • No. of natural satellites: 27 moons till 2021
  • Surface temperature: (-200 C)
  • Like Venus, Uranus also rotates from east to west.
  • Very thin layer of rings like saturn.
  • Surface covered with frozen ice (methane and ammonia) on small rocky core.


Image Credit: NASA
  • Eighth planet from the sun and last one in our solar system.
  • Distance from the sun in AU: 30
  • Orbital Period: 164 Years
  • Rotational Period: 15.9 H
  • No. of natural satellites: 14 moons till 2021
  • Surface temperature: (-200 C)
  • Very thin layer of rings like saturn.
  • Surface covered with mostly of hydrogen, helium, and methane.

Axis of Rotation

Planetary axis of rotation

Pluto and The Dwarf Planets

Dwarf planets are celestial bodies smaller than the normal planets and cannot able to classified as a planet because they are not behaving like a planet or lacking in some properties to be classified as a planet.

Why Pluto is not a Planet?

Pluto is an example of a Dwarf planet. Before 2006 Pluto was considered the 9th planet of our solar system. But due to lacking in some technicality like irregular rotation orbit, long period of orbital time, smaller than regular planets, etc. Pluto is not fit to the planet category and considered a Dwarf planet since 2006. Other than Pluto – Ceres, Makemake, Haumea, Eris are also falling into the Dwarf planet category.

Asteroids and Meteoroids

These are the small rocky material revolving around the sun, which cannot be able to form themselves as a planet. There is an asteroid belt in between the Mars and Jupiter where 1.1 million asteroids are rotating larger than 1 km size. And the largest one among them is Ceres & Vesta.


A comet is a small celestial body similar to asteroids but covered full of ice and a frozen surface, because of this when the comet comes closer to the sun its body starts heating up and begins to release gases in space and create a long tail behind it.

Comets are revolving around the sun in a very long elliptical path and the majority of comets we see are came from the Oort cloud, which is situated at the end of our solar system, and after that interstellar medium of space begin.

This is the basic introduction to the solar system.

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