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‘The Solar System’ is the name given to the planetary system of

which the Earth is part. It comprises 8 planets, moons, comets,

meteors, asteroids & dwarf planets which are all held together by

the gravitational pull of a star, named either the Sun or ‘Sol’.

Formation of the solar system:

The formation of the Solar System is estimated to have begun 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the centre, forming the Sun, while the rest flattened into a proto planetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

The Planets:

The known planets in the solar system can be divided into two

groups. The four planets closest to the sun: Mercury, Venus, Earth &

Mars are called the ‘terrestrial planets’. The outer four planets are

called the ‘gaseous giants’ or ‘Jovian planets’. The terrestrial & Jovian

THE SOLAR SYSTEM

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planets are divided by a belt of asteroids between Mars & Jupiter.

Pluto was demoted to the status of ‘Dwarf planet’ giving it home

among similar sized objects & asteroids which make up the Kuiper

Belt.

End of the solar system:

It is difficult to calculate exactly where our solar system ends. It ends

at a point at which objects are no longer affected by the sun’s

gravitational pull. The farthest reaches of the solar system are

thought to be surrounded by a great halo: Oort cloud; home to

millions of comet nuclei & small icy rocks.

Voyager 1 & 2 are the farthest reaching man-made objects in the

solar system. In 2004, Voyager 1 cleared the termination shock, the

area where solar winds begin to slow down & increase in

temperature as they come up against interstellar winds. Voyager

probes will continue transmitting data for several more decades, but

it would take thousands of years for them to reach the nearest star,

Alpha Centauri.

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4.1 THE SUN:

In the grand scheme of the universe, the sun in just another middle

aged star. Its stellar classification, G2, denoting its yellowish

colouring & its surface temperature (5000°-6000° kelvin) is not

extraordinary either; there are countless G2-type stars.

Fusion:

In the sun, Hydrogen nuclei collide with one another to form Helium

atoms. In this process, called ‘fusion’, mass is transferred into

energy, which is explained by Einstein’s famous equation: 𝐸 = 𝑚𝑐2.

The period during which sun generates energy through fusion is

called ‘Main sequence’. Our sun is estimated to be 5 billion years old

& its main sequence will last another 5 billion years.

Solar Layers:

The atmosphere of the sun is

composed of several layers, mainly

the photosphere, the chromosphere

and the corona. It's in these outer

layers that the sun's energy, which

has bubbled up from the sun's

interior layers, is detected as

sunlight.

Sunspots:

These are minor regions where the temperature of the photosphere

is cooler than its surroundings. Sunspots are the result of string

localised magnetic field & follow a cycle of 11 years.

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4.2 MERCURY

Mercury is the smallest and closest to

the Sun of the eight planets in the Solar

System, with an orbital period of about

88 Earth days. Seen from Earth, it

appears to move around its orbit in

about 116 days, which is much faster

than any other planet. It has no

known natural satellites. The planet is

named after the Roman deity Mercury;

the messenger to the gods

Mercury has almost no atmosphere. Its surface is heavily cratered

due to impacts from meteorites.

4.3 VENUS

Venus is the second planet from

the Sun, orbiting it every

224.7 Earth days. It has no natural

satellite. It is named after the Roman

goddess of love and beauty. After

the Moon, it is the brightest natural

object in the night sky, bright enough to

cast shadows. Venus is a terrestrial

planet and is sometimes called Earth's

"sister planet" because of their similar

size, gravity, and bulk composition.

It is the hottest planet in solar system. It rotates on its axis from east to west. Therefore, on Venus the sun rises in west & sets in east.

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4.4 EARTH Earth, also known as Terra, is the

third planet from the Sun,

the densest planet in the solar system,

the largest of the Solar System's for

terrestrial planets, and the only celestial

body to accommodate life. It is home to

millions of species, including billions of

humans.

The Earth takes 365.26 days to orbit the sun & 23.93 hours revolve

once around its axis which is tilted 23.5° to the planet’s orbit.

4.5 THE MOON

The Moon (Latin: Luna) is the Earth's

only natural satellite. Although not the

largest natural satellite in the Solar System,

it is, among the satellites of major planets,

the largest relative to the size of the object

it orbits and, after Jupiter's satellite Io, it is

the second densest satellite among those

whose densities are known.

The Moon is in synchronous rotation with Earth, always showing the

same face with its near side marked by dark volcanic maria that fill

between the bright ancient crustal highlands and the prominent

impact craters . It is the most luminous object in the sky after

the Sun. It takes moon 27.3 days to revolve around earth.

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4.6 MARS

Mars is the fourth planet from the Sun

and the second smallest planet in the

solar system, after Mercury. Named

after the Roman god of war, it is often

described as the "Red Planet" because

the iron oxide prevalent on its surface

gives it a reddish appearance.

Mars’s atmosphere is consists of 95%

of carbon dioxide & remaining 5% of Argon & Nitrogen. Average

surface temperature is 60° Celsius. Because of this water exist on

mars in frozen & vapour form.

4.7 JUPITER

Jupiter is the fifth planet from the

sun and the largest planet in the solar

system. It is a gas giant with mass one

thousandth of that of the sun but is

two and a half times the mass of all

the other planets in the Solar System

combined.

Jupiter is primarily composed

of hydrogen with a quarter of its mass being helium. There are also

moons that were first discovered by Galileo Galilei in

1610. Ganymede, the largest of these moons, has a diameter greater

than that of the planet Mercury.

at least 79 moons, including the four large moons called the Galilean

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The Giant Red Spot is its most notable feature. It is a giant storm

which flows anti-clockwise across in area of 24,000 km in length &

12,000 km in width.

Saturn is the sixth planet from the

sun and the second largest planet in

the Solar System, after Jupiter. It is

named after the Roman god of

agriculture. Saturn is gas giant with

an average radius about nine times

that of Earth. While only one-eighth

the average density of Earth, with its

larger volume Saturn is just over 95 times more massive.

One of the greatest fascinations of the solar system is the Rings of

Saturn. They have often earned Saturn the title of the most attractive

planet in solar system.

larger than the planet Mercury and is the only moon in the Solar

System to retain a substantial atmosphere.

4.9 URANUS

Uranus is the seventh planet from the Sun. It

has the third-largest planetary radius and

fourth-largest planetary mass in the Solar

System. Uranus is similar in composition

to Neptune, and both are of different

chemical composition to the larger gas

giants Jupiter and Saturn. For this reason,

astronomers sometimes place them in a

4.8 SATURN - 82 Moon

Titan, Saturn's largest and the Solar System's second largest moon

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separate category called "ice giants".

It is the coldest planetary atmosphere in the Solar System, with a

minimum temperature of −224.2 °C and has a complex, layered cloud

structure, with water thought to make up the lowest clouds, and

methane the uppermost layer of clouds. In contrast, the interior of

Uranus is mainly composed of ices and rock.

4.10 NEPTUNE

Neptune is the eighth and farthest

planet from the sun in Solar System.

It is the fourth-largest planet by

diameter and the third-largest by

mass. Among the gaseous planets,

Neptune is the densest. Neptune is

17 times the mass of Earth and is

slightly more massive than its near-

twin Uranus, which is 15 times the

mass of Earth but not as dense.

Neptune orbits the Sun at an average distance of 30.1 astronomical

units. It is named after the Roman god of the sea.

Neptune's atmosphere is notable for its active and visible weather

patterns. For example, at the time of the 1989 Voyager 2 flyby, the

planet's southern hemisphere possessed a Great Dark Spot

comparable to the Great Red Spot on Jupiter.

4.11 PLUTO & THE KUIPER BELT

Discovered in 1930, Pluto was originally classified as the ninth planet

from the Sun. Its status as a major planet fell into question following

further study of it and the outer Solar System over the ensuing 75

years. Starting in 1977 with the discovery of the minor planet 2060

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Chiron, numerous icy objects similar to Pluto with eccentric orbits

were found. The most notable of these was thes cattered disc

object Eris, discovered in 2005, which

is 27% more massive than Pluto.

Pluto has five known moons: Charon (the largest, with a diameter just over half that of Pluto), Nix, Hydra, Kerberos & Styx.

On July 14, 2015, the Pluto system is due to be visited by spacecraft for the first time. The New Horizons probe will perform a flyby during which it will attempt to take detailed measurements and images of the plutoid and its moons.

KUIPER BELT:

Kuiper Belt is a region of the Solar System beyond the planets,

extending from the orbit of Neptune (at 30 AU) to approximately

50 AU from the Sun. It is similar to the asteroid belt, but it is far

larger—20 times as wide and 20 to 200 times as massive. Like the

asteroid belt, it consists mainly of small bodies, or remnants from the

Solar System's formation. Although most asteroids are composed

primarily of rock and metal, most Kuiper belt objects are composed

largely of frozen volatiles (termed "ices"), such as methane,

ammonia & water. The Kuiper belt is home to at least three dwarf

planets: Pluto, Haumea, and Makemake. Some of the Solar System’s

moons, such as Neptune's Triton and Saturn's Phoebe, are also

believed to have originated in the region.

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4.12 MINOR BODIES IN SOLAR SYSTEM

4.12.1 ASTEROIDS

Asteroids are fragments of rock & metal which are greater than 50m

in diameter. On New Year’s Day 1801, the Italian astronomer,

Giuseppe Piazzi, discovered the first asteroid Ceres. Initially he

thought it was a comet, but its orbit was too slow & uniform. Some

scientists suggested it might be a planet between Mars & Jupiter. But

in 1802, second asteroid was discovered, named Pallas. This 2nd find

led William Herschel, the discoverer of Uranus, to offer a collective

name ‘asteroids’, meaning ‘Star-like’.

Many of the asteroids in the solar system are located in a band

between Mars & Jupiter called the ‘Asteroid Belt’. It is believed that

the belt is failed planet- the chunks of rock & metal were unable to

group together & form 5th terrestrial planet because of the strong

gravitational pull of Jupiter.

4.12.2 METEOROIDS

Meteoroids can be found throughout the solar system. They are

small fragments of rock & minerals, often the size of a grain of sand.

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Meteoroids are either the chipped away parts of grater bodies or are

remnants from the creation of the solar system.

SHOOTING STAR

When meteoroids collide with the Earth they burn up in the upper

atmosphere, creating a striking spectacle called Meteor.

METEOR SHOWERS

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4.12.3 COMETS

A comet is an icy small Solar System body that, when passing close to

the Sun, heats up and begins to outgas, displaying a visible

atmosphere or coma, and sometimes also a tail. These phenomena

are due to the effects of solar radiation and the solar wind upon the

nucleus of the comet. Comet nuclei range from a few hundred

metres to tens of kilometres across and are composed of loose

collections of ice, dust, and small rocky particles. The coma and tail

are much larger and, if sufficiently bright, may be seen from the

Earth without the aid of a telescope. Comets have been observed

and recorded since ancient times by many different cultures. Comets

are known as the ‘dirty snowballs’.

Comets have a wide range of orbital periods, ranging from several

years to several millions of years. Short-period comets originate in

the Kuiper belt or its associated scattered disc, which lie beyond the

orbit of Neptune. Longer-period comets are thought to originate in

the Oort cloud, a spherical cloud of icy bodies extending from

outside of the Kuiper belt to halfway to the next nearest star.