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Dwarf planets can be defined as a celestial body that orbits the Sun directly. It is big enough to be pulled into a roughly spherical shape by gravity and hasn't removed other smaller celestial objects out of their orbital path, unlike regular planets. According to astronomers, the solar system and the Kuiper Belt could contain up to 200 dwarf planets. These dwarf planets leave a scientific breadcrumb trail that scientists may follow back in time to learn more about the solar system's origins.
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Dwarf Planet
Dwarf planets are celestial bodies that orbit a star, are nearly spherical, and are frequently surrounded by big bodies like comets, asteroids, or other dwarf planets. Alan Stern, a planetary scientist, coined the term dwarf planet as part of a three-part classification system for planetary-mass objects in the Solar System: classical planets, dwarf planets, and satellite planets. Dwarf planets lack the gravitational forces required to pull in and gather all of the material in their orbits. Pluto, Eris, Ceres, Makemake, and dozens of other dwarf planets are officially recognised by the International Astronomical Union, which is the authority on the naming and classification of celestial objects.
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Criteria of Dwarf Planets
Dwarf planets are significant bodies that are too small to be considered planets. However, it is far too large even to consider falling into more modest groups. The IAU defines a planet as something that meets the following criteria:
- Revolves around the Sun in its orbit.
- Has enough gravity to reshape its mass into a spherical shape.
- Its circle is now devoid of more modest objects.
At this point, planets and dwarf planets differentiate. The gravity of a planet would either attract or repel smaller things that would obstruct its orbit. However, the dwarf planet's gravity is insufficient to get this going.
Dissimilarity Between a Dwarf Planet and a Planet
The region surrounding each celestial body is the only distinction between a planet and a dwarf planet. A planet has become gravitationally dominating as it has cleared the area around its orbit. In contrast, a dwarf planet has not, meaning it has not become gravitationally dominating, and its orbital region is shared with other bodies of similar size. Since the revised classification, Pluto, Ceres, and Eris, three objects in our solar system, have been designated as dwarf planets.
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How Many Dwarf Planets are There?
Salacia, Quaoar, Orcus, 2002 MS4, 2007 OR10, and Sedna are some examples currently being considered. Except for Sedna, a detached object — a particular type that applies to dynamic TNOs in the outer solar system – all objects are found in the Kuiper Belt or the Scattered Disc. According to estimates, up to 200 dwarf planets could be discovered if the entire Kuiper belt is examined, and up to 10,000 dwarf planets could be discovered if objects distributed outside the Kuiper belt are evaluated.
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Why was Pluto Considered a Dwarf Planet?
- Pluto was considered larger than Mercury for nearly 50 years, but with the discovery of Pluto's moon Charon in 1978, it was possible to correctly calculate Pluto's mass and find that it was significantly smaller than initial estimates. Pluto was around one-twentieth of the mass of Mercury, making it the tiniest planet in the solar system. It was also clear that it was a different body than any other planet since it had several uncommon properties, such as a big orbital eccentricity and a high orbital inclination.
- On August 24, 2006, classrooms all over the world received some dreadful news. Pluto, the celestial body discovered in 1930, had been formally categorised as a "dwarf planet" and removed from the solar system's family of planets. The International Astronomical Union (IAU) decided after the discovery of the slightly more massive asteroid Eris.
- Proponents of the proposal argued that if Pluto was given the title of "planet," so should similarly sized objects, such as Ceres, which was previously classified as a big asteroid. Beyond Neptune, a newer class of smaller worlds known as dwarf planets reigns supreme, including Pluto, a long-time favorite. Beyond our solar system, tens of thousands more planets have been identified. They're known as exoplanets by scientists (Exo means "from outside").
- In essence, the phrase refers to any planetary-mass object that meets two basic conditions but is neither a planet nor a natural satellite. It must, for starters, be in direct orbit around the Sun and not a moon orbiting another body. Secondly, it must be big enough to have assumed a spherical shape due to gravity. And, unlike a planet, it is unlikely to have cleared the area around its orbit.
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Asteroids: Dwarf or Not?
Asteroids are stony rocks that circle the Sun. The majority are found in the main asteroid belt, which lies between Mars and Jupiter's orbits. Asteroids are not dwarf planets. Asteroids are rocks that circle the Sun, particularly in the asteroid belt between Jupiter and Mars. Because most asteroids do not form a spherical shape, they are not classified as dwarf planets.
Points to Remember
- Up to 200 dwarf planets could exist in the solar system and Kuiper Belt.
- Dwarf planets orbit a star, are almost spherical and are typically surrounded by large things such as comets, asteroids, or other dwarf planets.
- Planetary scientist Alan Stern coined the term dwarf planet as part of a three-part classification system for planetary-mass objects in the Solar System: classic planets, dwarf planets, and satellite planets.
- The sole difference between a planet and a dwarf planet is the territory surrounding each celestial entity. A planet has cleared the orbital area around it, whereas a dwarf planet has not, implying that it has not become gravitationally dominant.
- Pluto, the celestial entity discovered in 1930, was formally classified as a "dwarf planet" and removed from the solar system's family of planets on August 24, 2006.
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Sample Questions
Ques: What are planetary-mass moons? (2 marks)
Ans: Several celestial bodies have the appearance of dwarf planets. Former dwarf planets may still retain an equilibrium shape or indications of active geology; planetary-mass moons, which fit the physical but not the orbital requirement for dwarf planets; and Charon, arguably a double dwarf planet in the Pluto–Charon system. Triton, for example, is classified as both a former dwarf planet and a planetary-mass moon.
Ques: What is a Dwarf Planet? (2 marks)
Ans: The "dwarf planets" are all objects that resemble a planet in some way, despite not being one of the eight dominating worlds (Mercury through Neptune). A dwarf planet, according to the best definition thus far, is something that appears like a planet yet isn't one. Dwarf planets are solar system bodies that have grown large enough to become spherical due to their gravitational attraction.
Ques: Describe in brief the dwarf planet: Makemake. (4 marks)
Ans: Makemake is a dwarf planet beyond Pluto's orbit that orbits the Sun. Makemake was found on March 31, 2005, a few days after Easter, by astronomers at Palomar Observatory. 2005 FY9 was the previous name for it. Makemake was discovered by scientists at Palomar Observatory on March 31, 2005, a few days after Easter, and is named after the creator god of the Polynesian residents of Easter Island. Because Makemake has a diameter of almost 1,400 kilometres (900 miles), gravity has moulded it into a dwarf planet and a plutoid, which was verified in 2008. Makemake is a reddish planet that takes 306 years to orbit the Sun. It has one moon, which was identified in 2015 using Hubble Space Telescope images. It has one moon and a rotational period of 7.771 hours.
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Ques: Who discovered Pluto and how? (3 marks)
Ans: Clyde Tombaugh discovered something that will change our understanding of our Solar System forever. He was working at Percival Lowell's observatory, which the great astronomer made famous. After spending many hours at the telescope exposing photographic plates and months examining them for clues of a planet, Tombaugh discovered what he was looking for. Tombaugh began comparing two plates collected in January of that year, which displayed a location in the constellation of Gemini, on the afternoon of February 18, 1930, at 4 p.m. A small thing flitted across the frame as he shifted between the plates. Tombaugh has discovered a brand-new world!
Ques: What is a celestial body according to the International Astronomical Union (IAU)? (1 mark)
Ans: According to the International Astronomical Union (IAU), a celestial body is the one that (a) has cleared the area around its orbit, (b) has enough mass to overcome rigid body forces and assume a hydrostatic equilibrium (almost round) shape, and (c) is in orbit around the Sun.
Ques: What prompted astronomers to come up with a new definition for a planet? (2 marks)
Ans: Astronomers from all over the world gathered under the auspices of the International Astronomical Union for more than two years to debate a new meaning for the word planet. Before being presented to the IAU General Assembly, the conclusions of these debates were routed through a Planet Definition Committee. Due to debate and further discussion, the definition changed, culminating in a final consensus and vote.
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Ques: Ceres was once referred to as an asteroid or small planet. Explain. (2 marks)
Ans: Ceres was originally classified as a planet when it was discovered in 1801, orbiting in the asteroid belt between Mars and Jupiter. Ceres lost its planetary designation in the 19th century because astronomers could not clarify its size and shape, and numerous additional bodies were identified in the same vicinity. Ceres has been considered an asteroid or small planet for almost a century.
Ques: Is Charon, Pluto's satellite, a dwarf planet? (3 marks)
Ans: Charon is currently only thought of as Pluto's satellite. Charon's classification as a dwarf planet in its own right may be considered in the future. Charon may be classified as a dwarf planet because it is similar in size and orbit to Pluto, rather than a satellite circling a planet. Charon's position as a dwarf planet is based on the fact that its centre of gravity revolves outside of the system's primary, Pluto. Instead, this gravitational centre, known as the barycentre, is found in open space between Pluto and Charon.
Ques: What exactly are plutoids? (3 marks)
Ans: Plutoids are celestial bodies that orbit the Sun at a semi-major axis greater than Neptune's. They have enough mass for their self-gravity to overcome rigid body forces and acquire a hydrostatic equilibrium (near-spherical) shape and have not cleared the orbital neighbourhood. Even if they are big enough to be shaped by self-gravity, satellites of plutoids are not plutoids themselves. Pluto and Eris are the two known and named plutoids. As science advances and discoveries are discovered, more plutoids are predicted to be identified.
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