Modern Physics

dwarf planets

Dwarf planets are those that are not massive enough to be the dominant stars in their region.

Planets considered dwarfs are not massive enough to be considered planets.

The International Astronomical Union (UAI), in August 2006, defined the characteristics necessary for a star to be considered a planet in the Solar System. To be considered a planet, the celestial body must:

  1. Orbiting around the Sun ;
  2. Be large enough that its gravity makes it spherical;
  3. Have a mass greater than the sum of the masses of its orbiting neighbors; in other words, to be a dominant object in its region.

What is a dwarf planet?

It is precisely this third prerequisite that planets considered dwarfs do not meet. Dwarf planets are those whose masses are very small, so that they are not the dominant stars in their orbits and have moons that have a mass of very close value.

In our Solar System, there are five planets classified as dwarfs: Ceres, Pluto , Haumea, Makemake and Eris. The first is located in a region between the orbits of Mars and Jupiter called the Asteroid Belt. The others are beyond Neptune , in a region called the Kuiper Belt, and are called plutoids.


Illustrated image of Ceres

In Roman mythology, Ceres is the goddess of harvest. This dwarf planet was identified in 1801 by the astronomer Giuseppe Piazzi and is located between the orbits of Mars and Jupiter, in a region called the Asteroid Belt, making it the closest dwarf planet to Earth. Its composition is rocky material, has a mass of approximately 9.45 x 10 20 kg , gravity of 0.26 m/s 2 and a diameter of 950 km.


Pluto is the Roman god of the dead, equivalent to Hades in Greek mythology. This dwarf planet was discovered in 1930 and has three moons: Charon (also called Charon), which was discovered in 1978, Nix and Hydra, observed by the Hubble telescope in 2005. Pluto’s mass is about 1.30 x 10 22 kg, its gravity is 0.65 m/s2, its diameter is approximately 2300 km and it has a translation period of 248 years.

Until 2006 Pluto was considered a planet, but after the decision of the International Astronomical Union, it was downgraded to the category of dwarf planet.


Haumea is the name of the Hawaiian goddess of fertility. This dwarf planet is the fastest rotating object in our Solar System, completing one revolution around itself in just four hours. However, its translation takes place in 285 years. Due to this rapid rotation, it assumes an oval shape, with an average diameter of 2200 km and a surface temperature of -240 °C.


The name Makemake comes from the fertility goddess of Rapanui mythology. Astronomers have observed signs of nitrogen, ethane and methane frozen on the surface of this dwarf planet that takes 310 years to go around the Sun, has an average diameter of 1450 km and a surface temperature of -238 °C.

Illustrated image of Eris

The name Eris comes from the Greek goddess of discord. This dwarf planet has an approximate diameter of 2400 km, a mass of 1.70 x 10 22 kg, a gravity of 0.80 m/s 2 and a translation period of 557 years!

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