Solar System and The Earth

Our solar system consists of group of planets which are gravitationally bound together to The Sun. 

Celestial bodies -

• The sun, the moon and all those objects shining in the night sky are called celestial bodies. 

Stars-

•  Some celestial bodies are very big and hot. They are made up of gases. They have their own heat and light, which they emit in large amounts. These celestial bodies are called stars. The sun is a star. 

Constellations-

• Various patterns formed by different groups of stars are called constellations.Ursa Major or Big Bear is one such constellation

Saptarishi -(Sapta-seven, rishi-sages)-

•  It is a group of seven stars that forms a part of Ursa Major Constellation. 

Pole Star -

• The North star is called as Pole star

Planets-

• Some celestial bodies do not have their own heat and light. They are lit by the light of the stars. Such bodies are called planets.

A Satellite-

• It is a celestial body that moves around the planets in the same way as the planets move around the sun. 

The solar system consists of the Sun and its eight main planets, their satellites, asteroids, comets, meteors and other dwarf planets. 

The congregation of stars and planets is known as Solar System. Solar System is a small part of the system of the stars known as spiral nebula or the Galaxy. 

Some of the Facts about our Solar System-

• Our Solar system is part of Milky Way or Akashganga Galaxy.It is one among the hundreds of millions of galaxies present in the Universe. 

• The Sun is at the center of the Solar System. 

• The closest planet to Sun is Mercury and the farthest is Neptune. 

• Pluto is a dwarf planet – relegated from its status as the ninth planet. 

• Visualized from top, all the eight planets are observed to move around the Sun counter-clockwise in an elliptical orbit. 

• Most of the satellites have the orbital and spin directions similar to the planets.

Inner Planets -

• The first four planets closest to the Sun are composed of rocks and metals. They are also known as the terrestrial or inner planets. 

• The four planets closest to the Sun are—Mercury, Venus, Earth, and Mars. 

• They are similar to Earth. 

• All are solid, dense, and rocky. 

• None of the inner planets has rings. 

• Compared to the outer planets, the inner planets are small. 

• They have shorter orbits around the Sun and they spin more slowly. 

• Venus spins backward and spins the slowest of all the planets. 

Outer Planets-

• The next four planets which are away from the Sun are mainly composed of hydrogen and helium. 

• They are also known as the gas giants or outer planets. 

• Jupiter, Saturn, Uranus, and Neptune are the outer planets . 

• Sizes of the outer planets and their orbits are about ten times larger than the sizes and orbits of the inner planets. 

• They also have planetary rings made of dust and other small particles. 

• Only the rings of Saturn can be easily seen from Earth.

• Jupiter is the biggest planet in the Solar System and Mercury is the smallest.

Asteroid Belt-

• It is Located between the inner and outer planet. 

• The sun is in the centre of the solar system. It is huge and made up of extremely hot gases.

• The Sun is made up of 73% hydrogen and 25% helium. It also has trace amounts of oxygen, carbon, iron and other elements. 

• The sun is about 150 million km away from the earth.

• Distance from centre is 30,000 light years of the Milky Way. 

• Surface Temperature of sun is around 6000 K. 

Fact- Light travels at the speed of about 300,000 km per second. Yet, even with this speed, the light of the sun takes about eight minutes to reach the earth.

Different Layers of Sun-

The Visible Layer-

• The layer that forms the visible surface of the Sun is called the photosphere.

The innermost layer

• The innermost layer of the Sun is its core where its energy is produced through nuclear fusion. 

The outermost layer

• The outermost layer of the Sun’s atmosphere is called the corona.

•  The corona cannot be seen due to the brilliance of the photosphere.

• However, it is seen during a total solar eclipse when it is visible in its full glory. The corona extends all the way upto the Earth’s orbit and even beyond. 

• There are eight planets in our solar system.

• In order of their distance from the sun, they are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

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1.Mercury-

• It is closest planet to The sun. 

• It is smallest planet in our solar system. 

• It has fastest orbit around The Sun. 

• Its Rotation period is longer than its orbital (revolution) period. 

• It Can be seen from the earth only before sunrise and after sunset. 

• It does not have any natural satellites. 

 2.Venus

• It is Known as Earth’s twin. 

• Its surface is dominated with volcanic features and is dotted with continent-like highlands and folded mountain belt. 

• It is Hottest planet in the solar system. 

• It Revolves around the sun in clockwise manner while most others are revolving in anti-clockwise. 

• Revolves around the sun in clockwise manner while most others are revolving in anti-clockwise. 

• It does not have any natural satellites. 

• It is First planet visited by spacecraft. 

3.Earth

• It is the only planet delicately balanced by the conditions necessary for sustaining life. 

• Moon is the only natural satellite of the Earth. 

• It has water in all three states – liquid, solid and gas. 

The Moon-

• The Moon Our earth has only one satellite, that is, the moon. Its diameter is only one-quarter that of the earth.

• It appears so big because it is nearer to our planet than other celestial bodies.

• It is about 3,84,400 km away from us.

• The moon moves around the earth in about 27 days.

• It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth.

• The moon does not have conditions favourable for life. It has mountains, plains and depressions on its surface.

• Neil Armstrong was the first man to step on the surface of the moon on 20 July 1969.

4.Mars

• Mars is the red planet having a diameter about half of the Earth is our closest neighbour after Venus and It appears Earth-like.

• It is Known as the ‘Red Planet’ due to presence of iron-rich red soil.

• There are large dark areas on its surface called maria (meaning ‘seas’).

• Phobos and Deimos are the two moons of Mars.

• It has polar ice caps and traces of sub-terrestrial liquid water has been found. It has the largest known volcano (and second tallest mountain) in the solar system – Mons Olympus. 

5.Jupitor

• Jupiter is the largest planet of the Solar System.

• It has a small rocky core which may contain iron, silicon and other heavy elements and seems more like the Sun in its composition than the other planets.

• It weighs more than twice as much as all the other eight planets put together.

• It Has the shortest rotation period. 

• It is a gas giant, primarily composed of hydrogen and helium with no discernible solid surface.

• The most outstanding feature on its surface is the Great Red Spot, a long oval area.

• It has  a faint ring around it. 

• At present 67 moons of this planet has been discovered and some of them are Ganymede (largest moon in the solar system – bigger than Mercury), Callisto, Io (volcanic), Europa (has water-ice)etc.

6.Saturn-

• It is the second largest planet in the Solar system.

• It is visible to the naked eye. 

• It has three rings that girdle its equator and are  visible only through a telescope. 

• At present 62 moons of this planet has been discovered ans some of them are Titan(largest),Rhea etc.

7.Uranus

• It appears as a green disc with vague markings, even through the largest telescopes.

• Its colour is produced by the large amounts of methane and ammonia clouds in its outer atmosphere.

• It is third biggest planet of the solar system.

• It also has faint rings and have 27 moons(Miranda, Ariel, Umbriel, Titania, Oberon etc.).

• It is tilted sideways so that its poles lie where most other planets have their equators.

8.Neptune

• It was discovered in 1846.

• It is Farthest planet from the Sun.

• It is blue in colour because of methane and has a storm called ‘Great Dark Spot’.

• It has 14 moons and Triton is one of the largest moon.

• It rotates in Clockwise direction.

All planets, except Venus and Uranus, rotate on their axes in the anticlockwise direction. So, on all these planets, like on the Earth, the Sun rises in the east and sets in the west. Venus and Uranus rotate in a clockwise direction and as a result, on these two planets the Sun rises in the west and sets in the east. 

Asteroids, Meteorites and Comets- 

Asteroid-

• A small rocky planet orbiting the Sun between the orbits of Mars and Jupiter is called Asteroid.

• Asteroids circle the Sun and occupy a broadly disc-like environment known as the asteroid belt.

• They are made of rock or metal (mostly iron) or a combination of the two.

Meteors, meteoroids and meteorites-

Meteoroids-

The particles of dust and small rocks flying through space or randomly wandering through space, are called meteoroids.

Meteor -

It is the flash of light that we see in the night sky when a small chunk of interplanetary debris burns up as it passes through our atmosphere, also known as a shooting star or when meteoroids enters earth atmosphere they start burning and are called meteor. 

Meteorite -

If any part of a meteoroid survives the fall through the atmosphere and lands on Earth, it is called a meteorite . 

Material of Meteorites-

Meteorites are composed of iron, nickel and rock forming minerals.

Generally, they are classified into three broad groups based on the abundance of metallic and stony minerals they contain:

Stony (or stones)-siderite.

Iron (or nickel-iron) - aerolites. 

Stony-iron (having both stone and iron components)- siderolites. 

Majority of the meteorites discovered so far are of the stony type. 

Comets-

• They are tiny icy and rocky bodies that travel in highly elliptical orbits around the sun.

• There is formation of Tail behind the comet when they reach near to the Sun due to heating up of its water and gases .

• Some comets reappear at predictable time intervals e.g. Halley’s Comet. Its period of reappearance is 76 years. It was last visible in 1986.

Important One liner Points on Solar system

What is the largest planet in our solar system?

Answer: Jupiter. 

What is the smallest planet in our solar system?

Answer: Mercury. 

Which planet has the most moons?

Answer: Jupiter. 

What is the hottest planet in our solar system?

Answer: Venus. 

What is the coldest planet in our solar system?

Answer: Neptune. 

What is the closest planet to the sun?

Answer: Mercury. 

What is the farthest planet from the sun?

Answer: Neptune. 

What is the largest moon in our solar system?

Answer: Ganymede (orbiting Jupiter). 

What is the only planet known to have life?

Answer: Earth. 

What is the name of the asteroid belt located between Mars and Jupiter?

Answer: The Main Asteroid Belt. 

What is the name of the dwarf planet that was once considered the ninth planet?

Answer: Pluto. 

What is the name of the largest volcano in our solar system, located on Mars?

Answer: Olympus Mons. 

What is the name of the largest canyon in our solar system, also located on Mars?

Answer: Valles Marineris. 

What is the name of the spacecraft that landed on Saturn's moon Titan?

Answer: Huygens (part of the Cassini-Huygens mission). 

What is the name of the spacecraft that was sent to study Pluto and its moons?

Answer: New Horizons. 

Formation and Origin of the Solar System-

There are many hypotheis and theories regarding origin of universe,solar system and The earth and some of them are as follows-

Broadly these theories and hypotheis are divided into Two major groups-

Uniparental or Monistic Hypotheses-

This group of hypotheses is based on the assumption that the origin of the Earth and universe is from one parent body. 

It has been favoured by Kant, Laplace, Lockyer, Hoyle, Carl Weizacker, Herald Yuri and Kuiper. 

Biparental or Dualistic Hypotheses:

This group of hypotheses is based on the assumption that the origin of the Earth and universe is from Two parent body. 

It is supported by Buffon, Chamberlin and Moulton, James Jeans, Jeffrey, Russell etc.

Some of the popular hypothesis are as follows-

1.Nebular Hypothesis of Kant (1775)-

• It was suggested by Immanuel Kant.

• According to his hypothesis, the Solar System evolved from a single, large, flat, rotating nebula.

• Due to rotation of Nebula and effect of Gravitation on it ,This Nebula becomes more and more compressed and compact .

• Due to the Gravitation pull between the particles they  starts colliding and sticking which results in increasing their size and later they formed stars, planets, etc.

2.Nebular Hypothesis by Laplace(1796)

He modified the Kant nebular theory that due to contraction and condensation of the gaseous nebula, velocity of the hot gases spinning nebula increased tremendously. Centrifugal force became more than the force of adhesion.

• Hence, a ring of gaseous matter was thrown up.

• Eight concentric rings formed in our solar system.

• The planet was formed in each concentric ring.

3.Planetesimal Hypothesis by Moulton and Chamberlin(1905)

• They suggested that the solar system is formed due to interaction between the Sun and another star. 

• The gravity of the passing star have direct impact on the surface of the sun, which causes the removal of outer surface or layer of the sun.

• There is formation of the Bolts and these Bolts coming from the side nearer the star are thrown out to distances comparable with those of the giant plants.

• After the star was gone, the gaseous matter in these arms condensed into solid material and gradually drew together to form planetesimal and than planets.

A planetesimal is a rocky and/or icy body, and its size varies from a few km to several tens of km, and it was produced in the solar nebula. 

4.Jeans Tidal Theory(1919)

• It suggested that there is Intruding star and the Primitive sun and the present solar system is formed due to the impact of the the tidal force of the Intruding star on The Primitive sun . 

• There is formation of the Cigar shaped projection which came out of the Sun due to gravitational attraction of the passing star and this formed the parent body.

• There was cooling and condensation of This Cigar shaped object and planets were formed from this cigar shaped filament.

• This had a Cigar shape because when intruding star was far from sun than small mass was ejected but when it approached sun than large mass was ejected and than when it gain moved away then again small mass was removed or ejected .

5.Jeffery Collision Hypothesis(1929)

• It is known as collision hypothesis. 

• According to Jeffreys before the birth of our solar system, there were three stars in the universe.

• The first was our primitive sun, the second was its 'partner star,' and the third was an 'intruding star' approaching the 'companion star.'

• Due to this the  'intruding star' collided with the 'partner star.'

• There was head-on collision and in this collision the companion star was completely smashed and shattered, these broken portions  were scattered in the sky and also the leftover debris started revolving around the primitive sun.

• Due to the impact of the collision and explosion ,the intruding star was able to get free from the original sun's gravitational pull and gradually fade away from the cosmos.

• the companion star's debris led to formation of the planets of our solar system .

6.Binary Star Hypothesis by H. N. Russell: 

• He considered two initial bodies called as components, the Sun and its companion.

• One of these revolves around the other.

• When the  intruding star approached the companion then one filament was removed and formed the planets. 

Note- 

There was no collision in this hypothesis as suggested in jeffry’s hypothesis. 

7.Hypothesis of Yuri-Kuiper-

According to this hypothesis, there was a big cloud of dust and gases in the space.

It constituted a mixture of condensed water vapours, ammonia, methane like hydrocarbon gases and iron oxide dust.

Formation of ancestral Sun

• There was the compression in the components of big clouds due to the effect of light of stars. Due to this the central part of the cloud turns into ‘ancestral Sun’ by the process of condensation. 

Formation of Planets-

• In due course, the huge cloud of gas and dust rotating around the ancestral.

• Sun, also divided into turbulent eddies of uneven sizes.They collided with one another and formed ‘planetisimals’ (small planets) or ‘protoplanets’  and later formation of planets were there. 

8.Fred Hoyle’s Magnetic Theory(1958)

• According to this hypothesis there was differentiation of the nebular matter into Sun and the gaseous cloud due to fast rotation of the nebular mass. 

• Due to magnetic coupling between the Sun and the gaseous cloud there was the end of the process of differentiation  and igave rise to planets. 

9.Big Bang Theory-

• It is one of the most popular theory which explains the formation of the solar system and also its expansion. 

• This theory was first propounded by George Gamow in 1940s and Fred Hoyle and William Fowler led further development in this theory  . 

• Fred Hoyle an English astronomer coined the term  Big Bang .

As per the Big Bang Theory there were the following stages in the development of the universe.

(i) In the beginning, there was a tiny ball or singular atom and all matter forming the universe existed in one place in the form of this “tiny ball” .This tiny ball had very  small volume along with infinite temperature and infinite density.

(ii) 13.7 billion years the Big bang took place and the “tiny ball” exploded violently. 

Due to this explosion there was expansion of the universe and The expansion continues even to the present day.

This expansion was so rapid that within fractions of a second after the bang the universe came into existence. Thereafter, the expansion has slowed down.

Within first three minutes from the Big Bang event, the first atom began to form.

(iii) Within 300,000 years from the Big Bang, temperature dropped to 4,500K (Kelvin) and this gave rise to atomic matter.

Formation of Planets-

It is assumed that there were following stages of planet formation. 

Differentiation - Layer Formation. 

Cratering - Impacts and Scars. 

Flooding - Lava Covers Everything. 

Surface Evolution - Changing Landscape. 

Formation of Earth

In the first tens of millions of years of the Earth’s evolution, combinations of several factors such as

(a) impact of small bodies like meteorites. 

(b) gravitational compression. 

(c) squeezing together of matter . 

(d) heat from radioactive decay increased temperature of the Earth. 

Evolution of Lithosphere of Earth

• The earth during its primordial stage was mostly in a volatile state . 

• There was gradual increase in density and the temperature inside the earth and  As a result the there was separation of material inside the earth on the basis of its density. 

• Due to this the heavier material like iron etc. sink towards the center and the lighter moved towards the surface of the Earth. 

• Due to this kind of differentiation there was formation of different layers and these layers are called the crust, mantle, outer core and inner core. 

Evolution of Atmosphere and Hydrosphere-

• The early atmosphere either escaped into space or was swept into space by the solar wind. 

• But Degassing that is gases from volcano added methane , ammonia, water vapour, and the noble gas neon, but it lacked free oxygen. 

• As the earth began to cool the water vapor condensed and began to create and fill the earth's oceans.  Carbon dioxide dissolved in the oceans and was slowly turned into rock. 

• The earth’s oceans were formed within 500 million years from the formation of the earth. 

• Nitrogen containing compounds like ammonia ( NH3 ) and molecular nitrogen ( N2 ) are also emitted by volcanoes.

• Oceans began to have the contribution of oxygen through the process of photosynthesis.

• Eventually, oceans were saturated with oxygen, and 2,000 million years ago, oxygen began to flood the atmosphere.

Important one liner on our Solar system.

What is the center of our solar system?

Answer: The sun is the center of our solar system.

What is the largest planet in our solar system?

Answer: Jupiter is the largest planet in our solar system.

What is the smallest planet in our solar system?

Answer: Mercury is the smallest planet in our solar system.

What is the hottest planet in our solar system?

Answer: Venus is the hottest planet in our solar system.

What is the coldest planet in our solar system?

Answer: Neptune is the coldest planet in our solar system.

What is the fifth planet from the sun?

Answer: Jupiter is the fifth planet from the sun.

What is the seventh planet from the sun?

Answer: Uranus is the seventh planet from the sun.

What is the eighth planet from the sun?

Answer: Neptune is the eighth planet from the sun.

What is the asteroid belt?

Answer: The asteroid belt is a region between Mars and Jupiter that contains many small, rocky objects.

What is a comet?

Answer: A comet is a small, icy object that orbits the sun.

What is a meteor?

Answer: A meteor is a small piece of debris that enters Earth's atmosphere and burns up.

What is the Kuiper Belt?

Answer: The Kuiper Belt is a region beyond Neptune that contains many small, icy objects.

What is the Oort Cloud?

Answer: The Oort Cloud is a hypothetical region beyond the Kuiper Belt that is believed to contain many comets.

What is a solar eclipse?

Answer: A solar eclipse occurs when the moon passes between the sun and Earth, blocking the sun's light.

What is a planetary nebula?

Answer: A planetary nebula is a cloud of gas and dust that is formed when a star like the sun reaches the end of its life.

What is the name of the largest moon in our solar system?

Answer: Ganymede, a moon of Jupiter, is the largest moon in our solar system.

What is the name of the planet with the shortest day in our solar system?

Answer: Jupiter has the shortest day of any planet in our solar system, at just under 10 hours.

What is the name of the planet with the longest day in our solar system?

Answer: Venus has the longest day of any planet in our solar system, taking 243 Earth days to complete one rotation.

What is the name of the only planet in our solar system that rotates on its side?

Answer: Uranus is the only planet in our solar system that rotates on its side.

What is the name of the most distant man-made object from Earth in our solar system?

Answer: Voyager 1 is currently the most distant man-made object from Earth in our solar system.

What is the name of the closest star to our solar system?

Answer: Proxima Centauri is the closest star to our solar system, located about 4.24 light-years away.

What is the name of the phenomenon that causes the northern lights?

Answer: The northern lights, or aurora borealis, are caused by solar wind particles interacting with Earth's magnetic field.