Question & Answers

The Solar System is made up of all the planets that orbit our Sun. It is supposed to have been formed 4.6 billion years ago. Our Solar System consists of the Sun, 8 planets, 63 moons, minor planets, millions of smaller bodies like comets, dust particles, and gases. The Solar System contains the Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

A lightyear is a measure of distance and not of time. Light travels at a speed of 300,000 km per second. Considering this, the distance light travels in one year is taken to be one lightyear. This is equal to \(9.461 \times 10^{12}\) km. The distance between the Sun and Earth is about 14.95 crore km. In terms of lightyears, it is about 8.31 minutes.

-> Inner Planets: Mercury, Venus, Earth, and Mars are called inner planets because they lie between the Sun and the belt of asteroids. These planets are made up of rock and metals and have relatively high density. These planets are also known as Terrestrial planets.

-> Outer Planets: Jupiter, Saturn, Uranus, and Neptune are called outer planets. These planets are made up of gas, and most of them are much larger than the inner planets. These planets have thick atmospheres consisting mostly of helium and hydrogen. They are also known as Jovian planets.

 Differentiation is the process of separation of lighter and denser materials. Through the process of differentiation, the earth-forming materials got separated into different layers.

• The modern theory regarding the origin of the universe is the Big Bang Theory. It is also called the expanding universe hypothesis. Edwin Hubble in 1920 provided evidence that the universe is expanding. As time passes, galaxies move farther and farther apart.
• Stages of Development:
  1. In the beginning, all matter forming the universe existed in one place in the form of a tiny ball or singular atom with an unimaginably small volume, infinite temperature, and infinite density.
  2. At the Big Bang, the tiny ball exploded violently, leading to a rapid expansion. It is now generally accepted that the event of the Big Bang took place 13.7 billion years before the present. The expansion continues even to the present.
  3. Within 3 lakh years from the Big Bang, the temperature dropped to 4,500 Kelvin and gave rise to atomic matter. The universe became transparent.

Criticism & Arguments:

• • Criticism: The expansion of the universe means an increase in space between galaxies. An alternative to this was Hoyle’s concept of the Steady State, which considered the universe to be roughly the same at any point of time. However, as more evidence became available about the expanding universe, the scientific community at present favors the argument of an expanding universe.
  • In Favor (Experiment): Take a balloon and mark some points on it to represent galaxies. Now, if you inflate the balloon, the points appear to move away from each other. Similarly, the distance between galaxies is found to be increasing, and thereby the universe is considered to be expanding.

Multiple Choice Questions

• A cold, dark, and empty space devoid of any matter.
• A tiny ball (singularity) with a very small volume, infinite temperature, and infinite density.  (Answer)
• A large, expanding nebula of gas and dust.
• A collection of scattered stars and galaxies.
  

• A. The time it takes for light to travel from the Sun to the Earth.
• B. The average distance between the Earth and the Sun.
• C. The distance traveled by light in one year at a speed of about 300,000 km/second.   (Answer)
• D. The amount of time light takes to reach the farthest planet in the solar system.
  

• A. Mercury
• B. Venus
• C. Jupiter   (Answer)
• D. Mars
  

• A. Terrestrial planets were formed after the Jovian planets had already used up all the gases.
• B. Terrestrial planets have higher temperatures which destroyed the gases over time.
• C. Solar winds blew away lighter gases from the inner planets, while the outer planets retained them due to their stronger gravity and colder temperatures.   (Answer)
• D. Jovian planets were formed by the collapse of giant black holes.
  

• A. The sinking of heavier materials (like iron) to the center and the rising of lighter materials to the surface.   (Answer)
• B. The gradual cooling of the Earth’s crust over billions of years.
• C. The formation of continents through tectonic plate movements.
• D. The separation of landmasses by oceans and seas.
  

• A. It was captured by Earth’s gravitational field from the asteroid belt.
• B. By a massive collision between the early Earth and a Mars-sized body.              (Answer)
• C. It condensed from a ring of gas that surrounded Earth during its formation.
• D. It was formed from the remains of a supernova explosion.
  

• A. 1, 2, 3, 4
• B. 3, 4, 2, 1
• C. 3, 2, 1, 4   (Answer)
• D. 2, 3, 1, 4
  

• A. Methane
• B. Ammonia
• C. Carbon dioxide
• D. Free Oxygen   (Answer)
  

• A. About 13.7 billion years ago
• B. About 4.6 billion years ago   (Answer)
• C. About 500 million years ago
• D. About 10 billion years ago
  

• A. A dead star that has collapsed under its own gravity.
• B. A vast, rotating cloud of gas and dust from which the system condensed.           (Answer)
• C. A large planet covered entirely in swirling atmospheric gases.
• D. A cluster of galaxies moving away from each other.