A dwarf planet is a celestial body that shares many characteristics of a regular planet but is not considered a planet because it lacks some features. Dwarf planets are similar to planets as they orbit around a star, are not a satellite, and are massive enough to be rounded by their own gravity. But they cannot be classified as a planet since they have not cleared their neighboring region.

Interesting Dwarf Planet Facts

• Dwarf planets orbit around the Sun.
• A dwarf planet has sufficient mass so that it has its own gravity which gives it a spherical shape.
• It is not a satellite.
• A dwarf planet falls into the category of neither planets nor natural satellites.
• The five known dwarf planets of the solar system are Ceres, Pluto, Haumea, Makemake, and Eris.
• Scientists believe that there are more than a hundred celestial objects in our solar system that could be identified as dwarf planets.
• The term ‘dwarf planet’ was adopted in the year 2006.

What are Dwarf Planets?

The term ‘dwarf planet‘ was adopted in the year 2006 when astronomical objects were discovered beyond the orbit of the planet Neptune. According to the International Aeronautical Unit or IAU, there are five recognized dwarf planets in the solar system. They are named Ceres, Pluto, Haumea, Makemake, and Eris.

According to the resolution B5 adopted by IAU to define planets and dwarf planets:

A “dwarf planet” is a celestial body that

(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces
so that it assumes a hydrostatic equilibrium (nearly round) shape2,
(c) has not cleared the neighborhood around its orbit, and
(d) is not a satellite.

Dwarf planets have not been known to mankind for that long time as compared to the other planets of the solar system. This is because of the fact that they are very small in size and are at a great distance from the Sun. Most of them cannot be seen by the naked eye and require the use of an advanced telescope.

Dwarf planets have found a place in popular culture. The unfolded mystery of dwarf planets has created curiosity in the minds of Writers and artists. Hence, they have been mentioned in a lot of books, TV shows, films, and even video games.

A dwarf planet is a celestial body or object that falls into the category of neither planets nor natural satellites. There are three main requirements for an object to be considered as a planet. Firstly, they must be orbiting the sun directly (which means they are not satellites). Secondly, they should have considerable mass with their own gravity. Lastly, they must-have cleared the space around their orbit that is they much be gravitationally influential.

Usually, any celestial body that does not meet one of these requirements is considered a dwarf planet. In general, dwarf planets do not need the third requirements to be considered as a planet.

Scientists believe that there are more than a hundred celestial objects in our solar system that could be identified as dwarf planets. Another 200 or so dwarf planets could be identified when the Kuiper Belt is explored. In total, they are believed to be 10,000 if we go beyond the Kuiper Belt.

 The five known dwarf planets of the solar system are explained as follows.

Pluto

Pluto is a dwarf planet that lies beyond the orbit of Neptune. It was considered as the farthest planet of the solar system, till 2006 after which it was declared as a dwarf planet. It is no longer considered as a planet because it could not fulfill all or even one of the three criteria required to be considered as one. It is not gravitationally dominant in its existence that is it does not clear its neighborhood.

Size and Distance

Pluto is 5.98 million kilometers or forty astronomical units away from the sun on average. Pluto takes nearly 248 years to orbit around the sun once. It takes 6.39 earth days to rotate about its own axis. Just like Uranus, Pluto rotates on its side.

The average radius of Pluto is about 1,180 km. Pluto’s orbit is highly elliptical because of which it was thought to be more to closer to the sun than Neptune. The surface area of Pluto is roughly equal to that of the country Russia.

Discovery

An astronomer called Urbain Le Verrier predicted the existence of another planet beyond the orbit of Neptune in the 1840s. Pluto was officially discovered by Clyde W. Tombaugh on 18 February 1930. Some scholars claim that ancient Indian astronomers knew about Pluto as early as 3100 BC and that it had been mentioned in the epic poem The Mahabharata. Pluto is named after the Roman god of the underworld.

Composition of Pluto

The dwarf planet is said to have a rocky core. It also has a mantle that is composed of solid water and a core that is covered by a mixture of ices of methane, carbon monoxide, and nitrogen. It is believed that Pluto has three times the amount of water as compared to earth.

Pluto’s satellites

Pluto is known to have five moons. The moons of Pluto are named Charon, Nix, Hydra, Kerberos, and Styx.  The largest of these is Charon. Pluto has only been visited by one spacecraft which is New Horizons by NASA.

Pluto’s appearance

Pluto appears to be brownish-yellow in color. However, the accurate color of Pluto was provided by NASA’s New Horizons. Pluto is actually slightly orange or reddish-brown in color but less orange than Mars.

Pluto is by far the most popular dwarf planet because of the media attention that it got after being declared a dwarf planet.

Ceres

Ceres is the largest known object in the entire asteroid belt. It lies between the orbits of Mars and Jupiter. It is closer to the orbit of planet Mars than Jupiter’s orbit. It is the only dwarf planet that lies within the orbit of Neptune that is the closest dwarf planet to the sun.

The name Ceres comes from Roman mythology. It was the name of the Goddess of agriculture. Initially, it was believed to be a planet between Mars and Jupiter which was undiscovered.

Size

It has a diameter of approximately 945 kilometers, making it the 33rd largest object in the solar system. It is the smallest dwarf planet known to us. It is close to 415 million kilometers away from the sun. It has an orbital period of nearly 4.6 years on Earth. The dwarf planet has an axial tilt of 4 degrees.

Discovery and exploration

It can hardly ever be seen with the naked eye from the Earth and even when it does, it is very dim because it is small in size. This dwarf planet was discovered by Giuseppe Piazzi on 1st January 1801. It was the first asteroid to be discovered. Ceres mainly consist of rock and ice. It may also have an ocean of water in the liquid state beneath its icy surface.

Composition, Surface, and Mass

It is believed to be having a rocky core. Above this rocky core, there is an icy mantle. It covers nearly one third the mass of the entire asteroid belt. It is rounded by its own gravity and is the only object in the asteroid belt to do so. Dawn, NASA’s robotic spacecraft was sent to orbit the dwarf planet on 6 March 2015.

Ceres Moon and Life expectancy

It is not often discussed as a potential center for lifelike other celestial bodies such as Mars, Europa, Titan, Enceladus or other moons of giant planets. However, since Ceres is known to have an icy mantle, that could have been an underwater Ocean at one point of time, some scientists speculate that life could have existed on the dwarf planet in the past. Some microorganisms may have come to earth from Ceres.

Haumea

Haumea is a dwarf planet that lies beyond the orbit of Neptune. It was discovered in 2004 and was declared as a dwarf planet on 17th September 2008 by the International Astronomical Unit or the IAU. The dwarf planet has been named after Haumea the Hawaiian goddess of childbirth. It has nearly one third the mass of Pluto and is elongated in shape.

Size

Haumea has a mean radius of 816 kilometers. It is the third-largest known object that lies beyond the orbit of Neptune after Pluto and Eris. It is 6.43 billion kilometers or 43.1 astronomical units away from the Sun on an average. It takes 283 years for Haumea to revolve around the sun once. It takes 3.9 hours to rotate about its own axis.

Composition and appearance

It cannot be seen by the naked eye, but it is very easily visible through a telescope. It is the third brightest object in the Kuiper Belt. Haumea is possibly composed of minerals of silicon such as olivine and pyroxene. Most of the rocky objects in the solar system are composed of these materials. It is also believed that most of the surface of Haumea is covered by a very thin layer of ice.

Haumea Satellites

Haumea has two natural satellites which are named as

• Hiʻiaka: Hi’iaka has a diameter of 310 km and orbits around Haumea every 49 days.
• Namaka: Namaka has roughly 1/10 the mass of Hi’iaka. It orbits around Haumea every 18 days.

Discovery and exploration

On 21st January 2017, a ring was observed around this dwarf planet. This was the first ring system discovered beyond the orbit of Neptune. The ring is nearly 2287 km in diameter. No spacecraft has visited this planet. However, a spacecraft was to be sent to Haumea, which will take approximately 14.25 years to reach the dwarf planet.

Life expectancy

No evidence of life has yet been found on Haumea but the idea of the presence of life in the past or the present cannot be completely eliminated. Currently, a spacecraft to Haumea is being planned and the proposed launch date is 25th September 2025. 

Makemake

Makemake is a dwarf planet that lies beyond the orbit of the planet Neptune and the largest known object in the Kuiper Belt. It is a trans-Neptunian object or a TNO. It has a mean diameter of approximately 1500 km which is two-thirds the diameter of Pluto.

Discovery and exploration

The dwarf planet was discovered on 31 March 2005 by a team of astronomers at the Palomar Observatory. The name Makemake comes from the culture of Easter Island. It is named after the god of fertility and the creator of humanity in the culture of Rapa Nui. It was officially sometimes referred to as Easter Bunny because it was discovered a few days after the festival of Easter.

Distance and visibility

Makemake is approximately 7.84 billion kilometers or 52.5 astronomical units away from the sun. It takes 7.7 hours to rotate about its own axis and its period of revolution is 309 years. It is quite dim to be seen by the naked eye but bright enough to be viewed through an advanced telescope. In the visible spectrum, Makemake appears to be red in color.

Appearance, Atmosphere, and Composition

It has an appearance that is redder than that of Eris. This could be because of the presence of Methane on a surface in abundance. Some other chemical compounds present on the surface of Makemake are ethane, tholins, and high mass alkanes.

Makemake lacks a proper atmosphere and the pressure above its surface is very low. Methane or nitrogen is expected to be the dominant part of its composition. The conditions on Makemake imply that the nitrogen present on the dwarf planet has depleted significantly over the course of time.

Satellite

Makemake is known to have one moon which is currently referred to as S/2015 or MK 2. The estimated diameter of the moon is 175 km. It has an orbital period of a little more than 12 days on earth. No spacecraft has visited Makemake up till now. If a flyby was to be sent to it, it would take around 16 years to reach the dwarf planet. 

Eris

Eris is one of the five dwarf planets in the solar system. It is located beyond the orbit of the planet Neptune that is it is a trans-Neptunian object. It was formed 4.5 billion years ago and is a part of the Kuiper belt. It is the second-largest known dwarf planet in the entire solar system.

Eris has a very cold surface and conditions which are too extreme for the presence of life and hence it is less likely that life could exist on this dwarf planet. 

Discovery

It was discovered by the Palomar Observatory in 2005. It was officially named in the September of the year 2006. Eris has been named after the Greek goddess of strife and discord. It is nearly 14 million kilometers or 96.4 astronomical units away from the Sun.

Size and distance

It has an orbital period of 558 years on earth. Its rotation period is approximately 8 hours. It has a radius of 1163 km, Eris quite similar to Pluto in terms of size. However, it is approximately three times farther away from the Sun.

Structure of Eris

It is so far away that the light of the sun takes around 15 hours and 15 minutes to reach Eris. The surface of this dwarf planet is believed to be similar to that of Pluto. It is known to have methane ice on its surface. Not much is known about the internal structure of this dwarf planet.

Satellite

The dwarf planet is known to have one natural satellite. It is called Dysnomia. It has been named after the Greek goddess of lawlessness. Eris and Dysnomia are the farthest known objects in the solar system as of today.