THE SOLAR SYSTEM

1. Eight major planets, 2. one dwarf planet (Pluto), 3. satellites and countless minor planets

4. asteroids, 5. meteors, and 6. comets orbit the Sun to form the solar system.

Located in Orion arm of Milky Way galaxy formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The vast majority of the system's mass is in the Sun, with most of the remaining mass

contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial

planets (mostly made of denser materials unlike outer gaseous plantes), are primarily composed of rock and metal.

The four outer planets, called the gas giants, are substantially more massive than the terrestrials.

The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of substances with relatively high melting points (compared with hydrogen and helium), called ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".

The asteroid belt, which lies between Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal.

Beyond Neptune's orbit lie the Kuiper belt and scattered disc, linked populations of trans-Neptunian objects composed mostly of ices. Within these populations are several dozen to more than ten thousand objects that may be large enough to have been rounded by their own gravity. Such objects are referred to as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris

Each of the outer planets is encircled by planetary rings of dust and other small objects. Bodies close to the Sun (the terrestrial planets) were formed from rocks and metals that

crystallized at high temperature, while the outer planets were formed from elements that form solids (condense) at low temperatures.

Origin of Solar System

The solar system was probably formed by the gravitational collapse of a huge cloud of gas and dust.

The reason for differences in planetary composition appears to be related to distance from the Sun.

Discovery and exploration

Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system (Sun at the centre). [Geocentric: Earth at the centre]

His 17th-century successors, Galileo Galilei, Johannes Kepler and Isaac Newton, developed an understanding of physics that led to the gradual acceptance of the idea that Earth moves around the Sun and that the planets are governed by the same physical laws that governed Earth.

Structure and composition

The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally

The Sun's four largest orbiting bodies, the gas giants, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic, whereas comets and Kuiper belt objects are frequently at significantly greater angles to it

Sun is rotating (counter-clockwise, as viewed from a long way above Earth's north pole). Kepler's laws of planetary motion describe the orbits of objects about the Sun. Following

Kepler's laws, each object travels along an ellipse with the Sun at one focus. A body's closest approach to the Sun is called its perihelion, whereas its most distant point from

the Sun is called its aphelion. The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt

objects follow highly elliptical orbits

All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic plane (The plane of the Earth's orbit around the Sun. The ecliptic plane is used as the primary reference plane when describing the position of bodies in the solar system).

Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum due to the differential rotation within the gaseous Sun.

The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets.

The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium (Same as that of Jupiter and Saturn). Jupiter and Saturn, which comprise nearly all the remaining matter, possess atmospheres composed of roughly 99% of these elements.

Those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points.

Objects farther from the Sun are composed largely of materials with lower melting points

Sun

The Sun was formed when a swirling cloud of dust and gas contracted, pulling the matter into its centre.

When the temperature at the centre rose to 1,000,000°C, nuclear fusion — the fusing of hydrogen into helium, creating energy—occurred, releasing a constant stream of heat and light.

Age 4.6 billion years Diameter 13,91,785km = 1.3 million kms Temperature 6000 C on surface and 16 million C in core Density 1.41 times that of water

[Density of water = 999.97 kg/m³; Density of Iron = 7870 kg/m³]Iron is (7870/999.97) = 7.87 times denser than water

Period of rotation 25days 9hrs Speed of rotation 7179.73 km/hr (Earth’s rotational velocity 1675Km/hr) Its large mass (3,32,900 Earth masses) produces temperatures and densities in its core high

enough to sustain nuclear fusion, which releases enormous amounts of energy, mostly radiated into space as electromagnetic radiation, peaking in the 400–700 nm band of visible light.

The Sun is a type G2 main-sequence star. Compared to the majority of stars in the Milky Way, the Sun is rather large and bright.

Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, are common, making up 85% of the stars in the galaxy

Photosphere

The photosphere is the bright outer layer of the Sun that emits most of the radiation, particularly visible light.

The photosphere is an extremely uneven surface. The effective temperature on the outer side of the photosphere is 6000°K (11,000°F).

Chromosphere

Just above the photosphere is the chromosphere. It is relatively a thin layer of burning gases.

Sunspot

A dark patch on the surface of the Sun is known as sunspot. Sunspots appear as dark areas because they are about 1500° cooler than the surrounding

chromospheres. The individual sunspot has a lifetime ranging from a few days to a few months. Each spot has a black centre or umbra, and a lighter region or penumbra, surrounding it. It has been suggested that the Sun is 1% cooler when it has no spot, and that this variation in

solar radiation might affect the climates of the Earth.

Solar Wind

The solar wind is a stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun, through the solar system at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius). It is made of plasma.

Effect on the Solar System

As the solar wind approaches a planet that has a well-developed magnetic field (such as Earth, Jupiter and Saturn), the particles are deflected

This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface.

The magnetosphere is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long trail on the opposite side.

The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines.

The solar wind is responsible for the overall shape of Earth's magnetosphere Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric

stripping by the solar wind. Venus, the nearest and most similar planet to Earth in the Solar System, has an atmosphere 100

times denser than our own, with little or no geo-magnetic field.

Plasma

one of the four fundamental states of matter, the others being solid, liquid, and gas. Plasma is simply ionized gas [convert (an atom, molecule, or substance) into an ion or ions, typically by

removing one or more electrons] Much of the understanding of plasmas has come from the pursuit of controlled nuclear fusion and

fusion power, for which plasma physics provides the scientific basis lightning and electric sparks are everyday examples of phenomena made from plasma. Neon lights

could more accurately be called "plasma lights", because the light comes from the plasma inside of them.

Aurora

An aurora is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions.

Auroras are caused by charged particles, mainly electrons and protons, entering the atmosphere from above causing ionisation and excitation of atmospheric constituents, and consequent optical emissions.

Planet

A celestial body moving in an elliptical orbit round a star, the Earth is known as planet. Planets are generally divided into:

(i) the Inner Planets (Mercury, Venus, Earth and Mars), and (ii) the Outer Planets (Jupiter, Saturn, Uranus, Neptune, and Pluto-dwarf planet).

Inner Planets

The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids

Composed mainly of silicates and metals The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no

ring systems. They are composed largely of refractory minerals, such as the silicates, which form their

crusts and mantles, and metals, such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to

generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes.

The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).

Mercury

Surface gravity: 1kg = 0.38 kg Mercury is similar to the Moon with a surface dominated by craters and a younger area of dark

plains presumably made from floods of lava.

Venus

Surface gravity: 1kg = 0.88 kg Venus is often considered to be the Earth's twin, but the two planets are not identical. Venus has high plateaus, folded mountain belts, numerous volcanoes, and relatively

smooth volcanic plains. The surface of Venus is totally obscured by a thick atmosphere composed mostly of carbon

dioxide, with clouds of sulfuric acid. It is much drier than Earth, and its atmosphere is ninety times as dense.

Earth

Surface gravity: 1 kg =1 kg The Earth is shaped like a ball, but it is not perfectly round. The force of the Earth's rotation

makes the world bulge very slightly at the equator and go a little flat at the North and the South poles. So the Earth is actually a flattened sphere, or a 'geoid'.

It is large enough to develop and retain an atmosphere and a hydrosphere. The Pacific Ocean contains the deepest places on the Earth's surface-the ocean trenches. The

very deepest is the Challenger Deep in the Mariana Trench which plunges 11022 m into the Earth's crust.

The Earth's Atmosphere

During the early stages of the Earth's formation, ash, lava, carbon and water vapour were discharged onto the surface of the planet by constant volcanic eruptions.

The water formed the oceans, while carbon dioxide entered the atmosphere or was dissolved in the oceans.

Clouds, formed of water droplets, reflected some of the Sun's radiation back into space. The Earth's temperature stabilised and early life forms began to merge, converting carbon dioxide into life-giving oxygen.

Mars

Surface gravity: 1 kg = 0.38 kg surface has been dynamic. Almost every geologic feature is gigantic. Three huge volcanoes, one

more than 28 km high exists at Mars. Wind action is also an important process: volcanoes, canyons, and landslides. There is evidence not only of stream action, but of catastrophic flooding Wind action is also an important process on Mars. In addition polar regions are covered with alternating layers of ice and wind blown sediment. It possesses an atmosphere of mostly carbon dioxide Its surface, peppered with vast volcanoes, such as Olympus Mons, and rift valleys, such as

Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago. [A rift valley is a linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault]

Its red colour comes from iron oxide (rust) in its soil Mars has two tiny natural satellites (Deimos and Phobos) thought to be captured

asteroids .

Asteroid belt

Millions of objects, remnants of planetary formation, circle the Sun in a zone lying between Mars and Jupiter. They are known as asteroids. Fragments of asteroids break off to form meteoroids, which can reach the Earth's surface.

Asteroids are small Solar System bodies composed mainly of refractory rocky and metallic minerals, with some ice

The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun.

It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter

Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids except the largest, Ceres, are classified as small Solar System bodies

Ceres

Ceres (2.77 AU) is the largest asteroid, a protoplanet, and a dwarf planet. It has a diameter of slightly under 1,000 km, and a mass large enough for its own gravity to pull it

into a spherical shape

Outer Planets

Outer Planets are Jupiter, Saturn, Uranus, Neptune and the dwarf planet - Pluto. Planetary bodies in the outer solar system were formed mostly of the lighter elements:

hydrogen, helium, and oxygen.

Hence, the satellites of the giant planets are composed mostly of ice, not of rock, like the inner planets.

The four outer planets, or gas giants (sometimes called Jovian planets), collectively make up 99% of the mass known to orbit the Sun. J

upiter and Saturn are each many tens of times the mass of Earth and consist overwhelmingly of hydrogen and helium;

Uranus and Neptune are far less massive (<20 Earth masses) and possess more ices in their makeup. For these reasons, some astronomers suggest they belong in their own category, "ice giants".

All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. The term superior planet designates planets outside Earth's orbit and thus includes both the outer planets and Mars.

Jupiter

Surface gravity: 1 kg = 2.53 kg It is composed mostly of gas and liquid swirling in complex patterns. Jupiter has no solid surface and hence no record of a geologic history. Its moons are, however, solid planetary bodies that contain geologic wonders. Jupiter's four large moons (Io, Europa, Ganymede, and Callisto), called the Galilean satellites

because they were discovered by Galileo in 1610

Saturn

1 kg = 1.07 kg mostly of hydrogen, and helium Saturn's rings for long have been considered as its most dramatic feature. The rings are probably made up of billions of particles of ice and ice-covered rocks, ranging from a

few micrometers to a metre or more in diameter. Titan , the second-largest moon in the Solar System, is larger than Mercury and the only satellite in

the Solar System with a substantial atmosphere. (Our Moon is the fifth largest natural satellite. Ganymede, a moon of Jupiter, is the largest in this solar system. At 5,268 km at the

equator, it is larger than Mercury, the dwarf planet Pluto, and three times larger than the Moon orbiting Earth.)

Uranus

1 kg = 0.92 kg no solid surface enveloped by a thick atmosphere of hydrogen and helium. In contrast to all other planets in the solar system, it is tipped and spun on its sides, that is its axis

of rotation lies nearly the plane of its orbit.

Neptune

1 kg = 1.18 kg Uranus and Neptune are called the twins of the outer solar system. Surrounded by thick atmosphere of hydrogen, helium and methane.

Pluto and Charon

1 kg = 0.30 kg The dwarf planet Pluto (39 AU average) is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the

adoption of a formal definition of planet. Pluto was moved into the list of Dwarf Planets along with Ceres and Eris. Charon, Pluto's largest moon

Kuiper belt

The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice

It extends between 30 and 50 AU from the Sun.

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.

Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.

Comets, composed of ice and dust, originated outside our solar system. Their elliptical orbit brings them close to the Sun and into the inner Solar System.

Comets are among the most spectacular and unpredictable bodies in the solar system. they are made of frozen gases (water, ammonia, methane and carbon dioxide) which hold

together small pieces of rocky and metallic minerals One of the larger comets is the Halley's Comet. The orbit of Halley's Comet brings it close to the

Earth every 76 years. It last visited in 1986.

Meteorite

Any solid debris origination from asteroids or comets or from outer space that fall to the Earth, the Moon, or another planet in the solar system.

Meteor is a body of matter travelling at a great speed through space which becomes luminous when enters into the atmosphere (mesosphere) at about 200 km above the Earth's surface, because it is heated by friction. Generally, this latter process dissipates the material into meteoric dust. A meteor is popularly termed a 'shooting star' or 'falling star'.

Largest Meteor Crater: A meteor crater in Arizona (USA) is 4,200 ft (1,300 m) deep is the largest meteor crater in the world. It was formed over 10,000 years ago.

Planets in the ascending order of proximity to sun

Diameter in kms; Diameter relative to Earth

Distance from Sun; Distance in Astonomical Units(AU)1 AU = Distance between Sun and Earth = 149.6 milliom kms

Mercury 4,878 = 0.38 57.9 mkm = 0.38Venus 12,104 = 0.96 108.2 mkm = 0.72Earth 12,576.3 = 1 149.6 mkm = 1Mars 6,794 = 0.54 227.9 mkm = 1.52Jupiter 143,884 = 11.44 778.4 mkm = 5.22Saturn 120,536 = 9.58 1.426 mkm = 9.57Uranus 51,118 = 4 2.87 mkm = 19.26Neptune 50,538 = 4 4.498 mkm = 30.18

Relative size of Planets

The Sun compared to the planets

Planets in the ascending order of proximity to sun

Temeperature in °C

Mercury +427 Venus +480 Earth +22 Mars -23Jupiter -150 Saturn -180 Uranus -214 Neptune -220

Planets in the ascending order of proximity to sun

Period of Rotation Period of Revolution

Mercury 58 days 87 daysVenus 243 days 224 daysEarth 23:56 hrs 365d, 5:48Mars 1.05 days 687 daysJupiter 9 hrs 11.86 yearsSaturn 10 hrs 29.46 yearsUranus 17 hrs 84.01 yearsNeptune 16 hrs 164.8 years

Planets in the ascending order of proximity to sun

Density relative to water(Taking, density of water = 1)

Mercury 5.43

Venus 5.24

Earth 5.51

Mars 3.94

Jupiter 1.33

Saturn 0.70

Uranus 1.3

Neptune 1.76

Planets No of Known MoonsMercury 0Venus 0Earth 1Mars 2Jupiter 61Saturn 31Uranus 21Neptune 11

Planets Rank accorging to sizeMercury 8Venus 6Earth 5Mars 7Jupiter 1Saturn 2Uranus 3Neptune 4

Planet Inclination angle to Ecliptic Orbital Velocity in km/sMercury 7° 47Venus 3° 35Earth 23° 29Mars 1° 24Jupiter 1° 13Staurn 2° 9Uranus 0° 6Neptune 1° 5Pluto (Dwarf planet)

17° 4

Heliocentrism vs Geocentric

astronomical model in which the Earth and planets revolve around a relatively stationary Sun at the center of the Solar System.

Kepler's laws of planetary motion

1. The orbit of a planet is an ellipse with the Sun at one of the two foci.2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.3. The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its

orbit.

Why is Venus sometimes called Earth's twin?

almost the same size, have about the same mass (they weigh about the same), and have a very similar composition (are made of the same material).

They are also neighboring planets.

However, Venus and Earth are also very different.

Venus has an atmosphere that is about 100 times thicker than Earth's and has surface temperatures that are extremely hot.

Venus does not have life or water oceans like Earth does. Venus also rotates backwards compared to Earth and the other planets.

Mars Compared to Earth

53% the diameter of Earth 10% the mass of Earth surface gravity on Mars is only 38% the gravity on Earth A day on Mars lasts 1.03 Earth days axial tilt on Mars is 25.19 degrees. Very close to Earth’s 23.5 degree tilt a year on Mars lasts about twice as long as an Earth year, the seasons are twice as long. The atmosphere of Mars is less than 1% the thickness of Earth’s atmosphere. Furthermore, it’s

made up of 95% carbon dioxide

The moon

Its diametre is only one-quarter that of the earth.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.Neil armstrong was the first man to step on the surface of the moon on 29 july 1969 .

All the planets except VENUS and URANUS rotate in anti-clockwise direction