Question

Which of the following is not a planet of our Solar system?
a)Sirius
b)Mercury
c)Saturn
d)Earth

Answer 1

Hint: Our solar system consists of the Sun and the 8 planets that orbit it. A planet is an astronomical object which is large enough to be rounded up by its gravity , orbits the Sun and has cleared its orbit of other smaller objects.

Complete answer: Our solar system has four inner planets and four outer planets. The inner planets are rocky in nature and hence called terrestrial planets. The outer planets are gas giants and called Jovian planets. Let us look at the options given to us.
Option (A) Sirius is a star and is also known as the Dog Star. It is the brightest star in the night sky and is 8.6 light years away from our solar system. The difference between a star and a planet is that unlike stars, planets have lower temperatures and cannot produce their own light.
Option (B) Mercury is the first planet from the Sun. It is also the smallest and the fastest planet of the solar system.
Option (C) Saturn is the sixth planet from the Sun. It is a gas giant and has icy rings around it.
Option (D )Earth is the third planet from the Sun. With an atmosphere made majorly of nitrogen and oxygen , and with two thirds of its surface covered with water, earth is the only planet where life is possible yet.

Therefore the correct answer is option (A) as Sirius is a star and not a planet.

Note: Apart from planets and the Sun , our solar system has other objects like comets, meteors, asteroids and dwarf planets. The dwarf planets like planets are spherical and orbit the sun. But unlike the planets, dwarf planets do not have enough gravity to clear its orbit of other smaller objects. Example of a dwarf planet is Pluto.