Inner Planets

Mercury, Venus, Earth and Mars are the inner planets because they are the nearest to the sun. They are also called terrestrial planets because they have rocky structures and are small in size.

Mercury is the planet closest to the sun. It is named after the Roman mythological god of commerce who is known for his speed because of the wings on his ankles. He served as messenger to the other Roman gods. Compared with the other planets, Mercury revolves around the sun the fastest because it has the smallest orbit to follow.

The planet Mercury is approximately 4,879 km in diameter and about 57 million km away from the sun. This planet can be seen in the early-morning or early-evening sky, so it is sometimes called ―the morning star.

Mercury has no water and atmosphere. This causes the surface of the planet to have temperatures that can reach up to 467°C when subjected to the rays of the sun. However, because of the lack of atmosphere, there is nothing to hold the heat of the sun’s radiation. Thus, Mercury can also have very low temperatures, sometimes reaching as low as –187°C in other parts, because it cannot retain the heat it absorbs. Mercury is covered with craters that were formed by rocks falling from space. These craters are completely dry. Given these characteristics, there is no possibility of life on Mercury.

In Mercury, a year is equivalent to nearly 87.97 Earth days. However, Mercury rotates on its axis very slowly that a day on the planet is equivalent to 58.65 Earth days. Mercury has no moon or satellite revolving around it.