What Makes A Dwarf Planet Different From A Planet
The term dwarf planet was coined by Alan Stern, a famous planetary scientist, when he introduced the three possible ways of categorizing planets: classical planets, such as Earth and Mars, dwarf planets like Pluto, and satellite planets, such as the Moon.
The term has been used to describe planets that are too small to be listed as full-fledged planets but too large to be considered asteroids or any other smaller celestial objects. In 2006, the term dwarf planets was adopted by the International Astronomical Union IAU, and here is how.
In January 2005, a new space object was discovered Eris. At first, it was considered more massive than Pluto, and for that reason, it was listed as the tenth planet in our solar system. A colossal controversy soon started, as not all scientists agreed with this new addition to the planets list.
The debate that followed was intense, and it came to an end during the IAU General Assembly in August 2006, when Resolution 5A: Definition of planet’ was introduced.
According to this resolution, all celestial bodies can be divided into three categories, as follows:
As reported by the International Astronomical Union, a planet is any celestial object orbiting around the Sun with enough gravity to overcome rigid body forces to pull its mass into a round shape.
This state is known as hydrostatic equilibrium, and the celestial object can clear its orbital path so that no other smaller bodies can be found near it.
Population Of Dwarf Planets
There is no clear definition of what constitutes a dwarf planet, and whether to classify an object as one is up to individual astronomers. Thus, the number of dwarf planets in the Solar System is unknown.
The three objects under consideration during the debates leading up to the 2006 IAU acceptance of the category of dwarf planet â Ceres, Pluto and Eris â are generally accepted as dwarf planets, including by those astronomers who continue to classify dwarf planets as planets. Only one of them â Pluto â has been observed in enough detail to verify that its current shape fits what would be expected from hydrostatic equilibrium. Ceres is close to equilibrium, but some gravitational anomalies remain unexplained. Eris is generally assumed to be a dwarf planet because it is more massive than Pluto.
In order of discovery, these three bodies are:
About The Dwarf Planets
Dwarf planets are nothing like Earth.
As their name implies, they are much smaller. Pluto and Eris, the largest of the dwarfs, have less than one-fifth the diameter of the Earth.
They have less mass, too. For example, Earth has about 6,400 times more mass than Ceres. Thats like comparing two killer whales to a guinea pig.
And dwarf planets are cold. Plutos average temperature is around minus 400 degrees Fahrenheit .
A photograph of Pluto and one of its five moons, Charon. Except for Ceres, all the dwarf planets have at least one moon. Charon is nearly half Plutos size. NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
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A Strange Ice Mystery
Haumea also has a surface that is mostly made of a kind of water ice unlike most of the other bodies in the Kuiper Belt.
This water-ice surface is shared by some of Haumea’s siblings that also appear to share the same orbit as the dwarf planet. This has led scientists to conclude Haumea and these icy bodies share the same origin and that they form the only family of related objects found in the Kuiper Beltthe ‘Haumean family.’
Using computer simulations, NASA scientists including Goddard Space Flight Center in Greenbelt, Maryland, post-doctoral student Jessica Noviello investigated the question “How did something as weird as Haumea and its family come to be?”
Computer simulations are necessary to achieve this due to the fact the dwarf planet is too far away to measure precisely using an Earth-based telescope, and Haumea is yet to be visited by a space mission.
These simulations allowed the team to ‘take apart’ Haumea and then rebuild it from scratch. The aim of this was to understand the chemical and physical processes that shaped the dwarf planet.
“To explain what happened to Haumea forces us to put time limits on all these things that happened when the solar system was forming, so it starts to connect everything across the solar system,” team member and Arizona State University in Tempe, professor of astrophysics, Steve Desch said in a statement. “There are a lot of odd, ‘gee whiz’ parts to Haumea, and trying to explain them all at once has been a challenge.”
The Changing Landscape Of The Solar System
The object Tombaugh had discovered was named Pluto, a name officially adopted by the American Astronomical Society, the Royal Astronomical Society in the UK and the IAU. It is a frigid world, billions of kilometres from Earth, and 30 times less massive than the then-smallest known planet, Mercury. But Pluto was not alone. It was found to have five satellites. The largest, Charon, was discovered in 1978. The smaller four were discovered using the Hubble Space Telescope in 2005, 2011 and 2012 and officially named Nix, Hydra, in early 2006 , Kerberos and Styx in 2013 by the IAU.
The view of our Solar System’s landscape began to change on August 30, 1992 with the discovery by David Jewitt and Jane Luu from the University of Hawaii of the first of more than 1000 now known objects orbiting beyond Neptune in what is often referred to as the transneptunian region. More generally these bodies are often simply labelled as Trans-Neptunian Objects .
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Dwarf Planets Plutoids And The Solar System Today
The IAU Resolution means that the Solar System officially consists of eight planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called dwarf planets was also decided on. It was agreed that planets and dwarf planets are two distinct classes of objects. The first members of the dwarf planet category are Ceres, Pluto and Eris, formerly known as 2003 UB313. Eris was named after the IAU General Assembly in 2006 Eris is the Greek god of discord and strife, a name which the discoverer Mike Brown found fitting in the light of the academic commotion that followed its discovery.
The dwarf planet Pluto is recognised as an important prototype of a new class of Trans-Neptunian Objects. The IAU has given a new denomination for these objects: plutoids.
Today the resolution remains in place and is a testament to the fluid nature of science and how our view of the Universe continues to evolve with changes made by observations, measurements and theory.
There Are More Dwarf Planets In Our Solar System Than You Know
Monday, April 4 2022 by Vahe Peroomian via The Conversation
The word planet came from the ancient Greek words that mean wandering star. That makes sense, because for thousands of years, people have watched planets change position in the night sky unlike stars, which appear fixed and unmoving to the naked eye.
Thats how the ancients discovered five of the planets: Mercury, Venus, Mars, Jupiter and Saturn. Astronomers using telescopes found Uranus in 1781, Neptune in 1846, and Pluto in 1930.
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Dwarf Planet Candidates Helped Scientists Find Planet 9
Thanks to a handful of debris orbiting farther away than Pluto, scientists this year found evidence that a rocky, Neptune-sized planet may lurk beyond the gaze of even our most powerful telescopes.
The story began in 2003, when Brown and his team at the California Institute of Technology discovered Sedna, a dwarf planet candidate that orbits far beyond the Kuiper belt, Plutos neighborhood of large, icy bodies 30 astronomical units away. Sedna maintains a steady orbit and comes within only 76 AU of the Sun at its closest approach.
Since then, scientists have spotted several more objects near Sedna, including 2012 VP113, found by Sheppard and colleague Chad Trujillo of Hawaiis Gemini Observatory. The pair noticed that their new object and the rest of these far-away objects had similar, steady orbits.
Back at Caltech, after reading Sheppards and Trujillos work, Brown and his colleagues set out to find the cause of such clustering, and after many hours of poring over models and simulations, they officially proposed that only a planet-sized body could exert enough gravitational pull to keep the far-away cluster of dwarf-planet-sized objects in steady orbits. This hypothesized planet was deemed Planet 9 .
Right now were doing surveys trying to find more dwarf planets, Sheppard said. If we find more and more of these, they can lead us to the much bigger, major Planet X.
What Is Dwarf Planet
Dwarf planets share many of the same characteristics as planets though there is one significant difference. The International Astronomical Unions definition of a dwarf planet is:
A dwarf planet is a celestial body that
The key difference is that a planet has cleared other objects in the area of its orbit while a dwarf planet has not.
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What Is A Dwarf Planet
A dwarf planet, as defined by the IAU, is a celestial body in direct orbit of the Sun that is massive enough that its shape is controlled by gravitational forces rather than mechanical forces , but has not cleared its neighboring region of other objects.
So, the three criteria of the IAU for a full-sized planet are:
Pluto meets only two of these criteria, losing out on the third. In all the billions of years it has lived there, it has not managed to clear its neighborhood. You may wonder what that means, not clearing its neighboring region of other objects? Sounds like a minesweeper in space! This means that the planet has become gravitationally dominant there are no other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence, in its vicinity in space.
So any large body that does not meet these criteria is now classed as a dwarf planet, and that includes Pluto, which shares its orbital neighborhood with Kuiper belt objects such as the plutinos.
Grundy Et Als Assessment
Grundy et al. propose that dark, low-density TNOs in the size range of approximately 4001000 km are transitional between smaller, porous bodies and larger, denser, brighter and geologically differentiated planetary bodies . Bodies in this size range should have begun to collapse the interstitial spaces left over from their formation, but not fully, leaving some residual porosity.
If Grundy et al. are correct, then very few known bodies in the outer Solar System are likely to have compacted into fully solid bodies, and thus to possibly have become dwarf planets at some point in their past or to still be dwarf planets at present. PlutoCharon, Eris, Haumea, Gonggong, Makemake, Quaoar, Orcus, and Sedna are either known or strong candidates .
There are a number of smaller bodies, estimated to be between 700 and 900 km diameter, for most of which not enough is known to apply these criteria. All of them are dark, mostly with albedos under 0.11, with brighter 2013 FY27 an exception this suggests that they are not dwarf planets. However, Salacia and Varda may be dense enough to at least be solid. If Salacia were spherical and had the same albedo as its moon, it would have a density of between 1.4 and 1.6 g/cm3, calculated a few months after Grundy et al.’s initial assessment, though still an albedo of only 0.04. Varda might have a higher density of 1.78±0.06 g/cm3 , published the year after Grundy et al.’s initial assessment its albedo of 0.10 is close to Quaoar’s.
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Dwarf Planets In Order From The Sun
Beyond Neptune is the trans-Neptunian region, which is where Pluto and several other dwarf planets are found. To date, this region is largely unexplored.
As mentioned above, a dwarf planet is in direct orbit of the Sun and has enough gravity to pull its mass into a round shape.
However, dwarf planets do not have sufficient gravity to attract or push away smaller bodies in order to clear their orbit and therefore, do not fit the definition of a planet .
The term dwarf planet, coined by Stern, was adopted by the IAU in 2006 as a category of sub-planetary objects.
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A New Class Of Objects And How To Define A Planet
The IAU has been responsible for the naming and nomenclature of planetary bodies and their satellites since the early 1900s. As Professor Ron Ekers, past president of the IAU, explains:
Such decisions and recommendations are not enforceable by any national or international law rather they establish conventions that are meant to help our understanding of astronomical objects and processes. Hence, IAU recommendations should rest on well-established scientific facts and have a broad consensus in the community concerned.The IAU decided to create a committee to gather opinions from a broad range of scientific interests, with input from professional astronomers, planetary scientists, historians, science publishers, writers and educators. Thus the Planet Definition Committee of the IAU Executive Committee was formed and quickly went about preparing a draft resolution to put to the members of the IAU. After the final meeting in Paris the draft resolution was completed. One crucial aspect of the resolution is described by Professor Owen Gingerich, Chair of the IAU Planet Definition Committee: “On the scientific side, we wanted to avoid arbitrary cut-offs simply based on distances, periods, magnitudes, or neighbouring objects”.
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Is Earth A Dwarf Planet
That means that according to the definition of the International Astronomical Union, the Earth cannot technically be considered as a planet and that it is, in fact, a dwarf-planet. ⦠There were seven earth sized objects discovered in orbit around an ultracool dwarf star forty light years away using this method.
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The Current Dwarf Planets In Our Solar System
After the 2006 General Assembly of IAU and their acceptance of this new category, three celestial bodies have been listed as dwarf planets: Pluto, Ceres, and Eris.
Later in 2008, Haumea and Makemake were also announced as dwarf planets in an IAU press release, even though it couldnt be proved at the time.
Today, these are the only five dwarf planets accepted by the International Astronomical Union. Lets see some details regarding them.
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Most Likely Dwarf Planets
The trans-Neptunian objects in the following tables, except Salacia, are agreed by Brown, Tancredi et al. and Grundy et al. to be probable dwarf planets, or close to it. Salacia has been included as the largest TNO not generally agreed to be a dwarf planet and a borderline body by many criteria. Charon, a moon of Pluto that was proposed as a dwarf planet by the IAU in 2006, is included for comparison. Those objects that have absolute magnitude greater than +1, and so meet the threshold of the joint planetâminor planet naming committee of the IAU, are highlighted, as is Ceres, which the IAU has assumed is a dwarf planet since they first debated the concept.
Orbital attributesThe First Dwarf Planets
The first dwarf planets discovered were often considered to be planets. Although Pluto is the most popular dwarf planet in our solar system, it was not the first to be discovered. The first dwarf planet discovered was Ceres, which was first observed in 1801. Ceres orbits in what we now know to be the Asteroid Belt, located between the orbits of and Jupiter. When Ceres was first discovered, astronomers believed they had found a new planet. After the discovery of Ceres, astronomers began discovering a number of other objects between Mars and Jupiter, all of which were initially assumed to be planets. However, by the 1850s, the number of planets in the solar system grew to 23. Since more and more objects were being discovered, astronomers decided to re-classify many of these objects as asteroids, and that included Ceres.
What initially ignited the debate about what it means to be a planet was the discovery of a dwarf planet called Eris, in 2005. Like Pluto, Eris orbits the sun in the far outer regions of the solar system, in an area known as the Kuiper Belt. When Eris was discovered, astronomers realized it was slightly larger than Pluto, yet it was not widely considered to be a planet. If Eris, which is larger than Pluto, was not considered a planet, it called into question whether or not Pluto should be a planet.
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