Solar system planets, order and formation: A guide

THE PLANETS

Planets are the heavenly bodies which receive light and heat from the Sun. They do not have

their own light. The total number of planets in the solar system are eight. In the order of their

distances from the sun, they are– Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The first four planets in order of their distance from the Sun are– Mercury, Venus, Earth and

Mars. They are called the terrestrial planets because they have solid, rocky surfaces. Two of the

outer planets, Jupiter and Saturn, are known as gas giants whereas the more distant, Uranus and

Neptune, are called ice giants.

Mercury has a thin atmosphere. The days are very hot, but at night temperature drops hundreds

of degree below freezing point. It is the smallest planet in our solar system. Venus is the hottest planet

due to its volcanic activities and thick atmosphere. It spins backwards. Earth, our home planet, is the

only planet which supports life due to its optimum amount of heat, light and oxygen. Mars, known

The Sun

• The word ‘planet’ is derived from the Greek word planas thai which means ‘wanderer’.

• The word ‘satellite’ is derived from the Latin word satellite which means ‘an attendant’.

• The word ‘solar’ is derived from a Latin word solaris which means sun.

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• TheThe eight planets in the order of their distance from the Sun

• Earlier Pluto was considered as the ninth planet. In 2006, the International Astronomical Union (IAU) established a new category, dwarf planet, for Eris and Pluto.

• The ring around the saturn were first seen by Galileo — a great astronomer of Italy, through

his telescope in 1610 A.D.

• The rotation time and revolution time of eight planets are as follows:

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Planets Rotation Time Revolution Time around the Sun

Mercury 59 days 88 days

Venus 243 days 225 days

Earth 24 hours 365 days and 6 hours

Mars Little over 24 hours 687 days

Jupiter 10 hours 12 years

Saturn 10.7 hours 29 years

Uranus 17 hours 84 years

Neptune 16 hours 165 years

• Earlier

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as the Red Planet, is a cold desert. Its atmosphere is too thin for liquid water to exist for long on the

surface. Jupiter, Saturn, Uranus and Neptune have rings. The rings around Jupiter are very faint and

hence, cannot be seen by naked eyes. The atmosphere of Jupiter, Saturn and Uranus is mostly made

up of hydrogen and helium. Other than these gases, Uranus has methane, which gives blue tint to it.

Neptune is similar in composition to Uranus, composed primarily of hydrogen and helium along with

traces of hydrocarbons and nitrogen. It also contains a higher proportion of ammonia and methane. THE EARTH–A UNIQUE PLANET

The earth, on which we live, is placed at third position

in order of the distance from the sun. It ranks fifth in size.

The earth completes one rotation on its axis from west to

east direction in about 24 hours, which makes one day. Its

revolution around the sun is covered in 365 days and 6 hours,

which makes one year.

In ancient times, it was believed that the earth is a

flat body, but in the fifth century CE, Aryabhatta, an Indian

astronomer declared that the earth is spherical in shape. Now,

the photographs of the earth taken from the space confirm its

spherical shape. The earth bulges slightly at the equator and

flattens at the poles.

Now let us learn the favourable conditions which support life on the earth.

Firstly, the earth receives moderate heat and light from the sun. This much quantity of heat and

light is just sufficient to evolve and sustain all forms of life on the earth’s surface. Other planets are

either very hot or very cold.

Secondly, about two-third of earth’s area is covered with water. Water is essential for human

beings, animals and plants. No life can exist without water.

Thirdly, the earth has an envelope of air around it. It contains gases, water vapours and dust

particles which help in supporting life on the planet. Earth’s atmosphere protects us from the

incoming meteoroids.

Photograph of the earth taken

from the space

On September 24, 2014, India became the fourth country in the world to reach the orbit of Mars

and the first to achieve it in its first attempt!

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On

SATELLITES

The heavenly bodies that revolve around their respective planets are called Satellites. Like the

planets, satellites also do not have their own light and heat. They reflect light, which they receive

from the sun. Each planet has one or more satellites, except the Mercury and the Venus. Our earth

has one satellite. We call it the Moon. As of 2015 Saturn has 53, Jupiter has 50, Uranus has 27,

Neptune has 13 and Mars has 2 satellites.

THE MOON–OUR NEAREST COMPANION

 

The moon is the closest celestial body to the earth. Its distance from the earth is about

3,84,000 km. The moon also reflects light which it receives from the sun.

The moon rotates on its axis and also revolves around

the earth. The period of rotation of moon on its axis and

that of revolution around the earth is the same, that is,

27.3 days. Due to the same period of both the movements,

only one side of the moon is visible from the earth. The

other side always remains invisible.

The moon has a barren land comprising of plains, valleys

and craters. Scientists believe that long ago, earth collided

with another space object and resulted in throwing a big

chunk of rocky material into the space and that led to the

formation of the moon.

The moon does not have atmosphere around it. It becomes extremely hot during the day time in

the light of the sun and extremely cold during night or in shadow. The temperature may increase to

more than 214°C during the day and falls down to - 184°C during the night. Thus, no life can possibly

exist on the moon.

Phases of the Moon

We have already learnt that one side of the moon gets illuminated by the sun, which is visible to

us. The position of the moon in relation to the sun changes every day. When the illuminated side of

the moon is fully hidden from our view, it is called the New Moon (Amavasya).

Saturn with its satellites

The Moon

 

The visible portion goes on increasing gradually day by day after the New Moon Day. At first, the

moon appears in crescent shape. On eighth day, half portion of the moon comes in our view. The

full moon becomes visible after 15 days when half of its revolution is completed. The day when the

moon is completely visible to us, is the Full Moon Day (Purnima). After this day, the decline of the

moon’s illuminated part starts. The illuminated part slowly disappears and the moon again comes to

the position of New Moon.

New Moon Full Moon New Moon

Various phases of Moon

Astronaut Neil Armstrong was the

first human to set foot on the moon.

He, along with Edwin Aldrin, landed

the Lunar Module of Apollo 11 on the

moon’s surface on July 20, 1969.

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Astronaut

The phases of the moon are used to determine the lunar dates and to fix the duration of lunar

months in India and Arab countries. The Hindu and the Muslim festivals, such as Deepawali and Eid,

are usually fixed on the basis of lunar dates and months.

OTHER CELESTIAL BODIES IN THE SOLAR SYSTEM

Apart from the sun, stars, planets and satellites, there are other celestial bodies also, like asteroids,

meteoroids and comets, that revolve around the sun.

Asteroids

Asteroids are rocky, space objects that orbit our Sun. These can be a few feet wide to several

hundred miles wide. Most asteroids orbit our Sun, a star, in a region of space between the orbits of

Mars and Jupiter known as the Asteroid Belt.

Meteoroids

Meteoroids are little chunks of rock and debris in space. They become meteors or shooting

stars when they fall through the earth’s atmosphere, leaving a bright trail as they are heated by the

friction of the atmosphere. Most of them break up in the atmosphere before they can strike the

surface as meteorites.

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Comet Hyakutake reached the closest point to earth in its path through the inner

Solar System on March 25, 1996

A crater is a depression which may be formed either by falling of a large meteor on the surface

of the earth or by the volcanic eruption. Meteor crater of North Arizona (USA) is nearly one

mile across, 2.4 miles in circumference and more that 550 feet deep.

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A crater

• astronomers: scientists who study celestial bodies.

• cluster: a group of the similar elements gathered closely in a bunch.

• crescent shape: a single curve that is broad in the centre and tapers to a point at each end.

• furnace: an enclosed chamber in which material can be heated at very high temperatures.

• gravitational force: a force that attracts any object with mass.

• self-luminous: objects having property of emitting light.

• spherical: a shape slightly flattened at the top.

Keywords

comet

Comets

Comets are the small bodies with a head and long luminous tail.

They are made up of dust and

frozen gases. They appear in the sky after a long period. A comet, known as Hailey’s comet, appears

in the sky after every 76 year interval.

hailey comet

a comet named death comet