What are planets exactly?
- A planet is a celestial body that revolves in an orbit around a certain star and receives all of its light from that star.
- Mercury, Venus, Mars, Jupiter, and Saturn are the only five planets visible from Earth with the naked eye. Uranus and Neptune, on the other hand, were only found after telescopes were constructed.
- Every planet, like the earth, spins once every 24 hours around its axis. The period of revolution of a planet is how long it takes to rotate around the sun.
- The terrestrial planets are built up by collisions and the accretion of planetesimals by gravitational attraction. The jovian planets are formed by gas accretion.
Theories on the formation of planets
Early theories
- Nebular Hypothesis
- Binary Theory
Modern Theory
Stages of formation of planets
The following are stages in the development of planets:
- The first stage of formation – The star is made up of gas lumps within a nebula. The gravitational force within lumps causes the formation of the core and the massive rotating discs of gases and dust that surround the gaseous core.
- The second stage of formation –The matter surrounding the core is condensing into smaller rounded objects. Planetesimals are a large number of smaller bodies that collide to form larger bodies.
- The final stage of formation – These planetesimals form and form larger planet bodies.
Our solar system came into being 5 billion years ago. The solar system consists of nine planets, numerous satellites and asteroids, and one sun.
Planets Categorization
The planets can be categorized into
- Inner planets or terrestrial planets, are the four planets closest to the Sun: Mercury, Venus, Earth, and Mars.
- outer planets are Jupiter, Saturn, Uranus, and Neptune. The gas giants are made up primarily of hydrogen and helium, the same elements that make up most of the Sun. These planets are also called as Julian planets.
Difference between Julian and Terrestrial planets
- Julian is formed by gaseous particles, whereas terrestrial planets are formed by solid particles.
- Solar winds blew away a lot of gases and dust from terrestrial planets, but this did not happen on Jovian planets since the terrestrial planet is smaller, its gravity is insufficient to hold the escaping gases.
Read More: The Evolution Of The Earth
