The Solar System


  • As the name implies, the solar system has something to do with the Sun, or Sol. (Incidentally, the words Sun, Moon, Earth, Mars, etc., should be capitalized since they are proper names.)
  • The Sun dominates and controls the solar system, mainly by its gravitational influence (keeping the planets in their orbits), but of course its light, heat, and other forms of energy are important also. We will learn of another important way that the Sun dominates its surroundings­­ through its magnetic field.
  • About 4.6 billion years ago, a giant cloud of dust and gas known as the solar nebula collapsed in on itself and began to form what would eventually become our solar system’s sun and planets.
  • Our solar system hosts the sun at its centre — a star so large that its gravitational pull keeps numerous planets, dwarf planets (such as Pluto), comets and meteoroids orbiting around it.

Origin of Solar System

  • Scientists believe a nearby exploding star, called a supernova, may have triggered the collapse of our solar nebula. According to this theory, the supernova’s explosion sent shock waves through space and those shock waves pushed parts of the nebula closer together, leading to collapse. The supernova may have even seeded material into the nebula, and this jettisoned material would have drawn even more matter toward the nebula’s growing mass.
  • The sun is at the centre of our solar system and is its largest object, accounting for 99.8% of the solar system’s mass. Our sun is a giant, raging ball of fire powered by nuclear reactions, and it provides the energy that sustains life on Earth.
  •  The life-giving star is a yellow dwarf star made up of gas: about 91% hydrogen and 8.9% helium, according to NASA. Compared with other stars, the size of the sun is relatively small and it’s just one of hundreds of billions of stars in our home galaxy, the Milky Way. 

Age of Solar System

  • Meteorites, or pieces of space rock that have fallen to Earth, have helped scientists figure out the age of the solar system.
  • Some of these small pieces of space rock, or meteoroids, have broken off moons or planets, and can yield interesting scientific information about the chemistry and history of their home body; others have been travelling around our solar system since that primordial dust-cloud collapse, before those planets even existed. 
  • The Allende meteorite, which fell to Earth in 1969 and scattered over Mexico, is the oldest known meteorite, dated to 4.55 billion years old.

Characteristics of Solar System

The planets of the solar system are divisible into two groups with similar properties.

  • Terrestrial planets are the inner planets such as Mercury, Venus, Earth, Mars are solid and relatively small and dense.
  • The Jovian or the giant planets are the outer planets, have many rings and satellites, and are composed primarily of hydrogen and helium gas. These are Jupiter, Saturn, Uranus, and Neptune. These are called the Jovian planets because of their large size and gaseous composition resembles Jupiter.
  • Then, there are Dwarf planets Pluto and Eris, Which are far away from the Sun with the orbital periods of 247.7 years and 557 years, respectively. They are dwarf because of their sizes; Pluto has diameter of 2300km, while Eris had diameter of 2400km.

Composition of Solar System

  • The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system.
  • Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%.
  •  The following table is a list of the mass distribution within our Solar System.
  • Sun: 99.85%
  • Planets: 0.135%
  • Comets: 0.01%
  • Satellites: 0.00005%
  • Minor Planets: 0.0000002%
  • Meteoroids: 0.0000001%
  • Interplanetary Medium: 0.0000001%

The Sun

  • Our Sun – the heart of our solar system – is a yellow dwarf star, a hot ball of glowing gases. Its gravity holds the solar system together, keeping everything from the biggest planets to the smallest particles of debris in its orbit. Electric currents in the Sun generate a magnetic field that is carried out through the solar system by the solar wind – a stream of electrically charged gas blowing outward from the Sun in all directions.
  • The Sun is the largest object in our solar system, comprising 99.8% of the system’s mass. Though it seems huge to us, the Sun isn’t as large as other types of stars.
  • Earth orbits the Sun from a distance of about 93 million miles. The connection and interactions between the Sun and Earth drive our planet’s seasons, ocean currents, weather, climate, radiation belts, and aurora. Though it is special to us, there are billions of stars like our Sun scattered across the Milky Way galaxy.

 Ten Things about the Sun

  • BIGGEST: If the Sun were as tall as a typical front door, Earth would be about the size of a nickel.​
  • MOST MASSIVE: The Sun is the centre of our solar system and makes up 99.8 percent of the mass of the entire solar system.
  • DIFFERENT SPINS: At the equator, the Sun spins once about every 25 days, but at its poles the Sun rotates once on its axis every 35 Earth days.
  • CAN’T STAND ON IT: As a star, the Sun is a ball of gas (92.1 percent hydrogen and 7.8 percent helium) held together by its own gravity.
  • RINGLESS: The Sun does not have any rings.
  • UNDER STUDY: Many spacecraft constantly observe the Sun, helping us keep an eye on space weather that can affect satellites and astronauts.
  • ENERGY FOR LIFE: Without the Sun’s intense energy, there would be no life on Earth.
  • NUCLEAR FUSION: The Sun’s core is about 27 million degrees Fahrenheit (15 million degrees Celsius).
  • Moonless: But orbited by eight planets, at least 5 dawrf planets, ten of thousands of asteroids, and upto three trillion comets and icy bodies.
  • WHAT WE SEE: The Sun’s visible surface sometimes has dark sunspots, which are areas of intense magnetic activity that can lead to solar explosions.

The Planets

  • There are eight planets in our solar system.
  • In order of their distance from the sun, they are:
    1. Mercury
    2. Venus
    3. Earth
    4. Mars
    5. Jupiter
    6. Saturn
    7. Uranus and
    8. Neptune

Inner Planets

  • These planets are very close to the sun.
  • They are made up of rocks.
  • Inner Planets are:
    • MERCURY- One orbit around sun – 88 days, One spin on axis – 59 days.
    • VENUS – One orbit around the sun – 255 days. One spin on axis – 243 days
    • EARTH – One orbit around the sun – 365 days. One spin on axis – 1 day Number of moons – 1
    • MARS – One orbit around the sun – 687 days. One spin on axis – 1 day, number of moons – 02

Outer Planets

  • Very far from the sun are huge planets made up of gases and liquids
    • JUPITER – One orbit around the sun – 11 years, 11 months about 12 years. One spin on axis – 9 hours, 56 minutes, number of moons – 16
    • SATURN – One orbit around sun – 29 years, 5 months. One spin on axis – 10 hours 40 minutes, number of moons – about 18.
    • URANUS – One orbit around the sun – 84 years. One spin around an axis – 17 hours 14 minutes, number of moons – about 17.
    • NEPTUNE – One orbit around the sun – 164 years. One spin on axis-16 hours 7 minutes, number of moons – 8


  • A satellite is a moon, planet or machine that orbits a planet or star. For example, Earth is a satellite because it orbits the sun.
  •  Likewise, the moon is a satellite because it orbits Earth. Usually, the word “satellite” refers to a machine that is launched into space and moves around Earth or another body in space.
  • Earth and the moon are examples of natural satellites. Thousands of artificial, or man-made, satellites orbit Earth. Some take pictures of the planet that help meteorologists predict weather and track hurricanes.
  • Some take pictures of other planets, the sun, black holes, dark matter or faraway galaxies. These pictures help scientists better understand the solar system and universe.

Still other satellites are used mainly for communications, such as beaming TV signals and phone calls around the world. A group of more than 20 satellites make up the Global Positioning System, or GPS.


  • Earth’s Moon is the only place beyond Earth where humans have set foot.
  • The brightest and largest object in our night sky, the Moon makes Earth a more liveable planet by moderating our home planet’s wobble on its axis, leading to a relatively stable climate.
  •  It also causes tides, creating a rhythm that has guided humans for thousands of years. The Moon was likely formed after a Mars-sized body collided with Earth.
  • Earth’s Moon is the fifth largest of the 200+ moons orbiting planets in our solar system.

Earth’s only natural satellite is simply called “the Moon” because people didn’t know other moons existed until Galileo discovered four moons orbiting Jupiter in 1610.

Asteroids, Meteoroids, Meteors, meteorite and Comets


  • Asteroids, sometimes called minor planets, are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago.
  • The current known asteroid count is 1,113,527.


These are objects in space that range in size from dust grains to small asteroids. Think of them as “space rocks.”


When meteoroids enter Earth’s atmosphere (or that of another planet, like Mars) at high speed and burn up, the fireballs or “shooting stars” are called meteors.


When a meteoroid survives a trip through the atmosphere and hits the ground, it’s called a meteorite.


  • Comets are cosmic snowballs of frozen gases, rock, and dust that orbit the Sun.
  • When frozen, they are the size of a small town. When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets.
  • The dust and gases form a tail that stretches away from the Sun for millions of miles. There are likely billions of comets orbiting our Sun in the Kuiper Belt and even more distant Oort cloud.

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