Question

How big is Mercury compared to the Earth?

Answer 1

Hint: There are nine planets in our solar system. These nine planets complete revolution around the Sun with the Sun as the centre. The nine planets are:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. The students should note that the order of planets is in the increasing order of distance from the sun and not in the increasing order of their sizes.

Complete answer:
The first planet that is closest to the sun is Mercury. This planet is named after the Greek God Hermes, which when translated to Latin, Mercury, the God of commerce.
The planet Mercury has the smallest tilt of its axis compared to any planet in the Solar system. The tilt of Mercury is about 1/30th of a degree. The orbital eccentricity of Mercury is the highest among all the planets in the solar system. This means that at perihelion, the distance of mercury from one of its axes, Sun, is only 66% of that of the distance at aphelion.
Mercury has a hard solid surface made of silicate crust and it is one of the only four terrestrial planets, along with Venus, Earth and Mars. Mercury does not have any natural satellites (i.e. moons). The time taken for Mercury to complete one rotation is equal to 58 days approximately on Earth, but the time taken for completing one revolution around the Sun is very short, equal to 88 days.
Let us have a look at the size of Mercury.
The radius of Mercury, $R_m=2439km$
The radius of Earth, $R=6378km$
The relative size of Mercury compared to Earth,
$r={\displaystyle \frac{R_m}{R}}={\displaystyle \frac{2439}{6378}}=0.382=38.2\mathrm{\%}\approx 40\mathrm{\%}$
Thus, the size of Mercury is approximately equal to 40% of that of the Earth.

Note: Even though Mercury is very closer to the Sun, the planet next to it, Venus, is termed as the hottest planet in the solar system. This is because there is an atmosphere of carbon dioxide around Venus, which traps the heat, thereby, making the planet hotter than Mercury.