The Planet System and its exploration!

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The planet

The planet is an astronomical body orbiting a star or a stellar object. In our universe, there are so many planets, the Planet Systems and we find many planetary systems.

Our solar system is one such planetary system as the planets in our system orbit around the Sun. So, it is needless to say that the Sun is the only star in our solar system, hence the name Solar.

The sun transmits energy to the planets in the form of heat and light(electromagnetic radiation). If there was no sun, there would not be any wind blowing, and the Earth would grow ice-cold.

There are more than 2,500 planetary systems found in our Milky Way galaxy alone, but it’s quite difficult to locate them.

The reason is that the nearest star to our Earth after the Sun is Proxima Centauri, which is 4.243 light-years away. Trying to find a planetary system is like traveling away from the sun and being unable to see the path. Hence, there are a whole lot of remote planets waiting to be discovered. However, astronomers study and measure the movements of stars and infer if the stars are influenced by other heavenly bodies.

Coming to our Solar System, there are 8 planets and 1 dwarf planet(Pluto) revolving around the sun. Asteroids, meteoroids, comets and other debris are also found in our system.

Formation of Planets / Planet System

It is observed that the gravitational collapse of a small part of a gigantic cloud led to the formation of our solar system. Most of the collapsing mass formed the centre of the Sun and rest of them formed disc-shaped structures later leading to the formation of Planets, asteroids and moons. Classification of Planets in our solar system are as follows:

Classification of Planets:

Planets are classified as in two categories:

  1. Terrestrial planets: These are rocky planets that is composed of primarily silicate rock or metals.
    • Mercury
    • Venus
    • Earth
    • Mars
  2. Jovian Planets: Jovian Planets categoriesed in two categories.
    1. Gas Giant: these are predominately made of Helium and hydrogen
      • Jupiter
      • Saturn
    2. Ice Giant: Made up of rock-ice, molecules of water, methane, and ammonia.
      • Uranus and
      • Neptune

Between Terrestrial and Jovian planets, there is asteroid belt, which consists thousands of chunks of rock(called asteroids) orbiting the Sun.

Terrestrial planets:


As all of us know, Mercury is the smallest and nearest planet to the Sun and moves faster than any other planet for the same reason. It has an extreme surface temperature from a maximum of 430°C on the bright side and -170°C on the dark side.

The planet atmosphere is so negligible, consisting of major constitutions of helium and hydrogen (captured from solar wind), a minimum constituent of sodium and oxygen, and tracers of neon, argon, and potassium.

  • Average orbital speed 47.87 km/s.
  • Day – 57 days 15 hours 30 minutes
  • Year – 87.97 Earth days
  • Diameter – 4879.4 km
  • Mass – 3.285 × 10^23 kg (0.06 of Earth mass)
  • Gravity – 3.7 m/s^2
  • Rotation – Anti-clockwise with an axial tilt of 2° and orbital inclination of 7°

Most of the surface of Mercury is heavily cratered due to the meteroids impact. This is due to the reason of it is being close to the Sun, which has got massive gravitational pull towards it. And, this brings about an impact on Mercury as well due to its negligible atmosphere.

The biggest crater ever found on Mercury is the Caloris Basin of about 1300 km and, it is believed to have formed due to the impact of an asteroid of around 60 km wide.

Apart from craters, Mercury has also got cliff like ridges (rupes) formed when the planet cooled and shrank around 4 billion years ago (when it was an young planet), buckling the surface of it in process.

For in-depth information on Planet Mercury, read our article: Mercury (The Smallest Planet in our Solar System)


Venus is the second closest planet to the Sun and is sluggish in its rotation as it spins backwards, hence has the longest solar day of 243 days in the entire solar system.

  • Average orbital speed – 35.02 km/s.
  • Day – 243 Earth days
  • Year – 224.7 Earth days
  • Diameter – 12,103 km
  • Mass – 4.867 × 10^24 kg (0.81 of Earth mass)
  • Gravity – 8.8 m/s^2
  • Rotation – Clockwise with an axial tilt of 2° and an orbital inclination of 3.39°

It has a similar core and internal structure as the planet Earth. Venus is the brightest object in the sky after the Sun and the moon because of its atmosphere majorly consisting of CO2, also bringing about the Greenhouse effect much stronger than on Earth.

Due to the greenhouse, Venus also happens to be the hottest planet having a surface temperature of about 480°C. It is hostile on Venus due to extreme temperatures, acidic clouds, and atmospheric pressure(90 times greater than Earth)

For in-depth information on Planet Venus, read our article: Venus (Hottest Planet in the Solar System)


The planet Earth, well known as “home”, the 3rd nearest planet to the Sun, the only planet to have discovered to sustain life, is the densest rocky planet covering about 70% of its surface with water. Hence it is also known as Blue planet. There are mainly four layers of Earth. They are

  • Inner core
  • Outer core
  • The mantle
  • The crust

The solid inner core holds a temperature around 6,600°C and the heat from this core is expected to melt the outer core and mantle, also circulate it in the form of convection currents. These convection currents cause the planet Earth to generate a magnetic field that would extend up to space as a Magnetosphere.

  • Average orbital speed – 29.78 km/s
  • Year – 365.26 days
  • Diameter – 12,756 km
  • Mass – 5.97219 × 1024 kg
  • Gravity – 9.807 m/s²
  • Rotation – Anti-clockwise with an axial tilt of 23.4°

Earth’s atmosphere is specially featured with Nitrogen, Oxygen , Carbon dioxide and other elements along with Ozone layer being there, due to which it screens out most of the harmful radiation from Sun making us safe. It infact avoids many meteroids hitting the Earth’s surface and preventing us from extreme cold as well. Earth has also got its own natural satellite, the Moon.


Moon, the only natural satellite is just a quarter size of the planet Earth. Yet, from Earth, the moon would look the same size as the massive Sun due to the fact that the Sun is 400 times as far as the lunar distance.

The moon has two faces, that is the near side and the far side. Only the near side is visible from the planet Earth because the moon has the takes same time of 27.3 days to orbit around the Earth as it takes to rotate around its own axis. The amount of near side visible to us depends on the amount of sunlight falling on the moon

  • Average orbital speed – 1.022 km/s
  • Diameter – 3,470 km
  • Mass – 7.3 × 1022 kg (0.12 Earth mass)
  • Gravity – 1.62 m/s^2 (1/6 times that of Earth)
  • Rotation – Anti-Clockwise with an axial tilt of 6.7°

Moon has got many highlands and lowlands wherein the highlands covered in craters are caused due to meteroite impacts and lowlands having large craters being covered by solidified lava forming dark areas called “Mare”, which literally means “Sea.” Maria is majorly found on the near side. The Moons atmosphere has negligible atmosphere due to which the footprints of astronauts must be visible even today on it.


Mars , also known as the red planet is the fourth nearest planet to the sun and is almost rocky. There appears to be some signs of kife on Mars due to canal like lines on its surface but later it was realised to be an optical illusion. The dust particles on the Mars gives its sky a Pinkish hue and the sunsets making appear Blue in color.

  • Average orbital speed – 24.13 km/s
  • Day – 24 hours 39 minutes 35 seconds
  • Year – 87.97 Earth days
  • Diameter – 4,878 km
  • Mass – 6.39 × 10^23 kg (0.107 times of Earth)
  • Gravity – 3.711 m/s^2
  • Rotation – Anti-clockwise with an axial tilt of 24° and an orbital inclination of 7°

A day on Mars is called “Sol”, unlike Earth. The northern hemisphere of Mars has many large plains of solidified volcanic lava and the southern hemisphere with large craters and impact resins.

The Martian atmosphere is thin unlike Earth consisting of fewer clouds and morning mists. It has got two irregular shaped moons named Phobos and Deimos. Scientists are not sure if they are exactly the moons or asteroids captured due to the Martian gravity.

Jovian planets:


The planet Jupiter is the fifth planet from the Sun and the innermost amongst the Jovian giant planets. Jupiter is the largest and the most massive planet. Jupiter is soo large that around 1300 Earths can be fitted in Jupiter. Jupiter has a small rocky core which is surrounded by an inner mantle of metallic hydrogen which is in turn covered by an outer mantle of liquid hydrogen and helium which merges into its gaseous atmosphere.

Jupiter rotates very fast on its axis that a pattern of belts/stripes is formed in its atmosphere, which runs parallel to the equator. It has a Great Red Spot, which consists of spiraling clouds. Jupiter also has got a thin, tenuous halo ring of tiny particles around it.

Average orbital speed – 13.07 km/s

Day – 9 hours 56 minutes

Year – 11.87 Earth years

Diameter – 142,984 km

Mass – 1.898 × 10^27 kg (317.83 times mass of Earth)

Gravity – 24.97 m/s^2

Rotation – Anti-clockwise with an axial tilt of 3.1° and orbital inclination of 1.3°

Jupiter has 79 moons out of which 53 are named. The most prominent ones are the 4 Galilean moons discovered by Italian astronomer Galileo Galilei with a telescope around 400 years ago. They are:






Saturn marks the sixth planet in the row and stands the second largest planet. Saturn consists of a small core of rock and ice surrounded by an inner mantle of metallic hydrogen (liquid hydrogen), which is covered by an outer mantle much like Jupiter. It also forms stripes, but obscured by overlying haze.

Saturn has got an attractive, extremely thin but wide system of rings which is less than of a kilometre thick but extends to 420,000 km from its surface. These rings are not solid, but are believed to be comets, asteroids and shattered moons of various sizes which broke before reaching the planets surface.

  • Average orbital speed – 9.69 km/s
  • Day – 10 hours 42 minutes
  • Year – 29.66 Earth years
  • Diameter – 120,536 km
  • Mass – 5.683 × 10^26 kg (95.16 times the mass of Earth)
  • Gravity – 10.44 m/s^2
  • Rotation – Anti-clockwise with an axial tilt of 26.7° and an orbital inclination of 2.49°


The planet Uranus is the seventh planet in the row and is the third-largest planet in our solar system. It consists of a dense mixture of different types of ice and gas around its solid core. Its atmosphere consists of traces of methane, hence the planet has git the blue-green hue and the clouds measure around -210°C. Uranus rolls instead of spinning due to its vast axial tilt(97.9°), hence making it more unique apart from being encircled by rings of rocks and dust.

  • Average orbital speed – 6.8 km/s
  • Day – 17 hours 14 minutes 24 seconds
  • Year – 84.13 Earth years
  • Diameter – 51,118 km
  • Mass – 8.681 × 10^25 kg (14.54 mass of Earth)
  • Gravity – 8.87 m/s²
  • Rotation – Anti-clockwise with an axial tilt of 97.9° and an orbital inclination of 0.77°

Around, 27 Uranian moons have been found, of which almost all are icy with diameter less than 160 km.


Neptune is the farthest planet from the sun, being about 4,500 million km far. Iy consists of small rocky core surrounded by a mixture of liquids and gases with its atmosphere consisting of Great and Small dark spots ( caused by windblown at 2,000 kmph) and Scooter (cirrus cloud).

Neptune has 6 tenuous rings and 13 known moons. Triton the largest moon of Neptune and is the coldest object in the solar system with the temperature of -240°C. Unlike other moons in the solar system, Triton orbits Neptune in the opposite direction to the planets rotation.

  • Average orbit speed – 5.43 km/s
  • Day – 16 hours 6 minutes
  • Year – 164.70 Earth years
  • Diameter – 49,258 km
  • Mass – 1.024 × 10^26 kg (17.15 times of Earth’s mass)
  • Gravity – 11.15 m/s^2
  • Rotation – Anti-clockwise with an axial tilt of 28.8° and an orbital inclination of 1.77°

Neptune orbit extends upto Kuiper belt consisting of mix of rock, ice being irregular in shape and also Dwarf planets.

Dwarf planets

A planet or a celestial object in a planet system will be considered as Dwarf planet if it does not satisfy the conditions to be a planet. Pulto was considered to be one of the planet in our planet system until 2006, but was removed and was put in dwarf planets classification which arised.

There are nearly 5 dwarf planets and they are

  • Ceres
  • Pluto
  • Haumea
  • Makemake
  • Eris

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