Solar System: Planets, The Sun and Celestial Phenomena

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Our planetary system is called the Solar System, as everything revolves around the Sun. The space that lies beyond our solar system is known as interstellar space.

Origin and Evolution of the Solar System

Theory	Year	Proponent
Gaseous Hypothesis	1755	Immanuel Kant
Nebular Hypothesis	1796	Laplace
Planetesimal hypothesis	1905	T.C Chamberlin
Tidal Hypothesis	1919; modified in 1929	James Jeans
Binary Star Hypothesis	1937	H.N. Russel
Supernova Hypothesis	1946	F. Hoyle

Facts About the Sun

It is the central celestial body of our Solar System. It is a star.
Age: It is believed to be 5 billion years old.
Composition: Mainly composed of hydrogen and helium. It has a liquid inner section surrounded by a gaseous outer covering.
Size: 13,92,000 km.
Temperature: It varies from 15 million degrees Celsius found at the core to 5,500 degrees Celsius observed at its surface.

Layers of the Sun

Sun’s Secrets: Key Phenomena and Their Impact on Earth

- Sun Spots: These are the dark patches visible on the surface of the Sun. They are dark because they are cooler than the surroundings.
- Solar Wind: It is a stream of plasma flowing outward from the Sun’s corona.
- Coronal Mass Ejection (CME): It refers to the release of plasma and magnetic field from the Sun’s corona. They occur when the Sun’s magnetic field lines undergo reorganize.
- Solar Cycle: It is the cycle that the Sun’s magnetic field goes through, approximately every 11 years. Every 11 years, the Sun’s magnetic field completely flips, and the Sun’s north and south poles switch places.

Solar Flares: These are large explosions from the surface of the sun that emit intense bursts of electromagnetic radiation.

- - They occur when the magnetic energy that is built up in the solar atmosphere is released suddenly.
- Auroras: They are formed when the charged particles released by the CME react with the different gases in the earth’s atmosphere.
  - Lights seen near the North Pole are called Aurora Borealis or northern lights.
  - Similarly, Aurora Australis or southern lights are the lights that occur near the South Pole.
  - Most of the auroras occur at a height of 97–1000 kilometres from the earth’s surface.
- Sun’s Halo: It is also known as ’22 degrees halo’. It is an optical phenomenon which occurs when sunlight refracts millions of hexagonal ice crystals suspended in the atmosphere. It forms a rainbow-coloured ring with a radius of approximately 22 degrees around the sun or the moon. Circular halos specifically are produced by cirrus clouds.
Space Weather: It is a type of weather created due to the activity on the Sun’s surface. It results in the variations in the space environment between the sun and Earth.

Planets

Planets are objects that orbit around a star in an elliptical path.

Dwarf Planets: The dwarf planets are small. They don’t have a distinct orbital path.
- There are four dwarf planets in the Kuiper Belt, viz. Pluto, Makemake, Haumea, and Eris. Another dwarf planet located in the main asteroid belt is Ceres.
Exoplanets: These are the planets which are located outside our Solar System.
Protoplanet: It is a celestial body orbiting around a star and thought to be developing into a planet. In 2022, the Hubble Space Telescope photographed a Jupiter-like protoplanet named AB Aurigae b.

Pluto: It is the largest among dwarf planets

Time taken to rotate on its axis: Six earth days
Time taken to revolve around the sun: 248 earth years
No. of Moons: 5. Charon is the largest
Rings: No

Classification of Planets

Inner Planets	Outer Planets
Mercury, Venus, Earth and Mars orbit near the Sun and are called Inner Planets. The inner planets are also called Terrestrial (Earth-Like) Planets. They are made up of a solid surface. They are dense due to the presence of an iron core.	Jupiter, Saturn, Uranus, and Neptune are called Outer Planets. The outer planets are called Jovian (Jupiter-like) Planets. They do not have a solid surface. They are less dense as they are made up of gases.

Planets and Important Facts

Planet	Order from the Sun	Time taken for rotation	Time Taken for revolution	No. of Moons	No. of Rings	Other Facts
Mercury	1	59 earth days	88 earth days	0	0	Fastest planet in our solar system that travels through space at 47 kilometres per second
Venus	2	243 earth days.	225 earth days	0	0	Hottest planet in our solar system It rotates on its axis backward, i.e., in clockwise direction. This implies that, on Venus, the Sun rises on the West and sets on the East.
Earth	3	About 24 hours	About 365 days	1	0	Shape: Oblate Spheroid Fifth-Largest Planet The only planet in the solar system with liquid water on its surface. Densest of all planets in the solar system
Mars	4	Little over 24 hours	687 earth days	2-Phobos and Deimos.	0	Appears like a reddish ball due to iron minerals on its surface
Jupiter	5	About 10 hours	12 earth years	80 Ganymede is the largest	Yes	Largest planet in our solar system. Mainly composed of gas and liquid and has no solid surface
Saturn	6	10.7 hours	29 earth years	83 Titan is the largest	Yes (7)	Composed of gas and does not have a solid surface
Uranus	7	17 hours	84 Earth years	27	Yes (13)	Known as the “Ice Giant” as most of its mass is a hot, dense fluid of icy materials-water, methane, and ammonia
Neptune	8	16 hours	165 earth years	14	Yes (9)	Known as Uranus’s twin because of the striking similarity in size, structure, and composition

PYQ. Which one of the following statements is correct with reference to our solar system? (2002)

The Earth is the densest of all the planets in our solar system
The predominant element in the composition of Earth is silicon
The Sun contains 75 percent of the mass of the solar system
The diameter of the Sun is 190 times that of the Earth

Answer: A

Kuiper Belt

The Kuiper Belt is a ring-shaped region located beyond the orbit of Neptune, spanning a distance of 30 to 55 astronomical units (AU) from the Sun.

This region is home to numerous icy bodies known as Kuiper Belt Objects (KBOs) or Trans-Neptunian Objects (TNOs), which are remnants from the early stages of the solar system’s formation.

Oort Cloud

It is a spherical collection of comets and small icy bodies that orbit the sun. It is located beyond the Kuiper Belt, in interstellar space.

Asteroids and Comets

Asteroid

Comets

These are rocky objects.
They have an elliptical orbit
The orbital period varies from 1 to 100 years
They are smaller
They do not produce a tail.

Types of Asteroids:

Main Belt Asteroids: These are located within the primary asteroid belt found between the orbits of Mars and Jupiter.
Trojan Asteroids: These asteroids share their orbital path with a large planet, maintaining a stable position either ahead of or behind the planet in its orbit.
Near-Earth asteroids. Asteroids that orbit close to the earth. For. E.g. Apophis

Examples: Vesta, Eros, Bennu

These objects are made up of frozen gas, dust etc
They have eccentric orbit
The orbital period can be 75 years to more than 100,000 years.
They are large.
They form a tail that stretches in a direction away from the Sun.

Examples: Hailey’s comet

In 2021, the Bernardinelli-Bernstein comet was discovered, making it the largest comet ever observed.

PYQ. What is the difference between asteroids and comets?

Asteroids are small rocky planetoids, while comets are formed of frozen gasses held together by rocky and metallic material.
Asteroids are found mostly between the orbits of Jupiter and Mars, while comets are found mostly between Venus and Mercury.
Comets show a perceptible glowing tail, while asteroids do not.

Which of the statements given above is/are correct? (2011)

1 and 2 only
1 and 3 only
3 only
1, 2 and 3

Answer: B

Meteors, Meteoroids and Meteorites

Meteoroids: These are rocky or metallic fragments in space, varying in size from tiny dust particles to small asteroids.
Meteor: When a meteoroid penetrates the atmosphere of Earth or another planet, it is referred to as a meteor. Commonly called “shooting stars,” meteors emit light as they burn up due to friction caused by their interaction with atmospheric molecules.
Meteorite: If a meteor survives its journey through the atmosphere and impacts the surface, it is classified as a meteorite.
Meteor Shower: A meteor shower occurs when Earth passes through a region with a high concentration of meteoroids, resulting in numerous meteors appearing simultaneously.These are space rocks ranging in size from dust grains to small asteroids. Meteor showers are generally named after a star or constellation that is close to where the meteors appear to originate in the sky.

Leonids Meteor Shower

The Leonids are a yearly meteor shower that reaches its peak around mid-November.
This meteor shower is composed of debris left by the comet 55P/Tempel-Tuttle, which resides in the Leo constellation. The comet completes an orbit around the Sun every 33 years.
The Leonids are often referred to as “fireballs” or “earth-grazer meteors” due to their bright appearance and long paths across the sky.
Approximately every 33 years, the Leonids transform into a meteor storm, characterized by a remarkable display of over 1,000 meteors per hour.

Geminids Meteor Shower

The Geminids meteor shower takes place annually in December.
It is caused by fragments from the asteroid 3200 Phaethon, which completes an orbit around the Sun approximately every 1.4 years.

Solar System: Planets, The Sun and Celestial Phenomena

Table of Contents

Origin and Evolution of the Solar System