Mercury
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The smallest and closest planet to the Sun
Mercury is the smallest planet in the solar-system and the closest one to the sun. It is named after the Roman messenger god Mercury because it moves quickly across the sky. Mercury is one of the four inner terrestrial planets, meaning it has a solid, rocky surface. Even though it is close to the Sun, it is not the hottest planet — that title belongs to venus.
Mercury is about 4,880 kilometers wide, which makes it just a little larger than earth’s Moon. It has no moons or rings. Because of its small size and closeness to the Sun, Mercury’s gravity is much weaker than Earth’s. A person who weighs 100 kilograms on Earth would weigh only about 38 kilograms on Mercury.
A year on Mercury, which is the time it takes to go once around the Sun, lasts only 88 Earth days. However, a day on Mercury, which is one full rotation on its axis, is much longer — about 59 Earth days. This means that one side of Mercury can face the Sun for a long time, becoming very hot, while the other side stays in darkness and becomes extremely cold.
The surface of Mercury is covered with craters, mountains, and plains, similar to the Moon’s surface. These craters were formed by asteroids and comets hitting the planet long ago. Mercury has almost no atmosphere, so there is nothing to protect it from space rocks or to trap heat. Temperatures on Mercury can reach about 430°C during the day and drop to around −180°C at night.
Mercury’s interior is made mostly of metal and rock. Scientists believe it has a large iron core, which takes up much of the planet’s size. It also has a very thin magnetic field and traces of gases like oxygen, sodium, and helium around it. These gases do not form a true atmosphere but create a thin exosphere.
Because Mercury is so close to the Sun, it is difficult to observe from Earth. Most of what we know about it comes from space missions. The first spacecraft to visit Mercury was Mariner 10 in the 1970s, and later the MESSENGER spacecraft studied the planet between 2011 and 2015. Scientists continue to study Mercury to learn more about how rocky planets like Earth formed in the early Solar System.
Mercury is about 4,880 kilometers wide, which makes it just a little larger than earth’s Moon. It has no moons or rings. Because of its small size and closeness to the Sun, Mercury’s gravity is much weaker than Earth’s. A person who weighs 100 kilograms on Earth would weigh only about 38 kilograms on Mercury.
A year on Mercury, which is the time it takes to go once around the Sun, lasts only 88 Earth days. However, a day on Mercury, which is one full rotation on its axis, is much longer — about 59 Earth days. This means that one side of Mercury can face the Sun for a long time, becoming very hot, while the other side stays in darkness and becomes extremely cold.
The surface of Mercury is covered with craters, mountains, and plains, similar to the Moon’s surface. These craters were formed by asteroids and comets hitting the planet long ago. Mercury has almost no atmosphere, so there is nothing to protect it from space rocks or to trap heat. Temperatures on Mercury can reach about 430°C during the day and drop to around −180°C at night.
Mercury’s interior is made mostly of metal and rock. Scientists believe it has a large iron core, which takes up much of the planet’s size. It also has a very thin magnetic field and traces of gases like oxygen, sodium, and helium around it. These gases do not form a true atmosphere but create a thin exosphere.
Because Mercury is so close to the Sun, it is difficult to observe from Earth. Most of what we know about it comes from space missions. The first spacecraft to visit Mercury was Mariner 10 in the 1970s, and later the MESSENGER spacecraft studied the planet between 2011 and 2015. Scientists continue to study Mercury to learn more about how rocky planets like Earth formed in the early Solar System.
What We Can Learn
- Mercury is the smallest planet and closest to the Sun.
- It has a rocky surface covered with craters.
- A year on Mercury lasts 88 Earth days.
- It has extreme temperatures and almost no atmosphere.
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