Which is the smallest planet

Which is the smallest planet in our solar system? And what about the whole universe? Read about it here!

According to the modern astronomy, the solar system consists of eight planets. So which is the smallest planet in the world?


In 1930 the American astronomer Clyde William Tobo discovered a previously unknown planet very far away in the solar system. It was decided to call it Pluto. In 1978, scientists were able to measure the transverse size of the planet.

According to their calculations it was 2,400 km. Therefore, Pluto was claimed to be the smallest planet in the solar system.

But science moves forward all the time. And the studies made in the 2000s showed that Pluto was just one of the objects of the so-called Kuiper Belt. This Belt consists of about 70 000 space ice objects. So Pluto is simply one of those objects. In 2005 scientists discovered another small “planet” which was the same size as Pluto. It was named Eris.


In 2006 scientists who were a part of the International Astronomical Union, concluded that both Pluto and Eris are not the real planets of the solar system. According to the new system, these objects were classified as dwarf planets.

Therefore, Pluto is not the smallest planet in size.

Nowadays Mercury is considered to be that.

Mercury's equator length is 4879 km. The Earth's equator is 12742 km long so Mercury has only 38% of Earth's diameter.

READ ALSO: What is the hottest planet

Although this planet is very small, Mercury is sufficiently dense. It mainly consists of iron and stone, and has a density of 5.4 grams per cubic centimeter. There is only Earth that has a higher density, due to the fact that our planet is bigger. Moreover, the density gets bigger as we move closer to the core. If Mercury was bigger than our planet it would be much denser.

If you stand on the surface of Mercury you can feel only 38% of the Earth's gravity. Because of Mercury’s high density the gravity on this planet is even higher than on Mars.

Mercury is the closest planet to the Sun. The distance between the Sun and Mercury is about 58 million km. The planet orbits the Sun in 88 Earth days. The physical characteristics of Mercury resemble the Moon. It has no natural satellites, but there is a kind of atmosphere. The planet has a large iron core.

There are craters of different ages on the Mercury's surface. Some of them are not totally safe.

The proximity to the Sun and a quite slow rotation of the planet make Mercury the planet with the most dramatic change in temperature in the solar system. The surface of Mercury is very loose which means it is a poor conductor of heat. Therefore, the planet's surface cools down and heats up quickly, but at a depth of 1meter the temperature becomes stable and can reach about +75 ° C.

Mercury is the least studied planet in the solar system. Therefore, scientists plan to launch two spacecrafts there in 2017. One of them will study the depth of the surface of the planet, and the second one will explore the magnetosphere and magnetic field.

What is, however, the smallest planet in the whole universe?

kepler 37b

The smallest of the planets in the universe known by men is called Kepler-37b. It is smaller than any other planet of the solar system, including Mercury. Its size is smaller than the size of the moon. The planet circles around the sun-like star in the Lyra constellation. The star’s mass is the 80% of the mass of the sun.

It is also smaller and cooler. Kepler-37b is 3 times closer to its star than Mercury is to the Sun. Therefore, temperature of the surface reaches 700 Kelvin degrees. A year lasts only 13 Earth days on this planet. Its surface consists of the rocky rivers of lead and zinc. The discovery of this extremely small planet became possible thanks to the "Kepler"- the space telescope launched in 2009.

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