The composition of planets in the solar system has been a point of debate among astronomers, planetary scientist, astrophysicist etc on the status of some planets. It is known that the planets, satellites, asteroids, comets, meteorites, etc are part of the solar system; traditionally the nine (9) recognized planets that make up the solar system as hitherto taught to children in primary schools range from a very tiny rocky planet to huge giants featuring fascinating ring system. Up till now the easy way to remember the order of the nine planets are mnemonics, “My Very Excellent Mother Just Send Us Nine Plantains and My Very Easy Method Just Simplifies Us Naming Planets. (Okoye, 2006) or My Very Educated Mother Just Served Us Nine Pizzas.
The name planet is derived from a Greek word, “Planѐtѐs, which means wanderer. Before the 2006 International Astronomers Union’s (IAU) new definition of the term (planet), it was simply described as “one of the celestial bodies in space other than a comet, meteor or satellite which revolves round the sun. In 1990 astronomers were able to avoid definitively resolving the question on Pluto’s status, because despite the new neighbours around Pluto, no kuiper belt object was larger than it. (Messeri, 2010) (Kuiper belt objects are planetary bodies found beyond Neptune).
Later, in 2003 an object in the kuiper belt was found to be more massive than Pluto and to be classified as a the tenth planet or kuiper belt object; if it were to be a kuiper belt object- Pluto might be classified as one. (Tytell, 2005). Because of this situation the IAU inaugurated a “Planetary Definition Committee” to formalize the definition of planet.
On August 24th, 2006, the IAU came up with an official definition of a planet after a heated debate. It resolves that planet and other bodies in the solar system, except satellites should be defined in three distinct categories in the following ways:
A 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) shape and
 (c) has cleared the neighbourhood around its orbit.
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) shape
(c) has  not cleared the neighbourhood around its orbit and                                                 (d) is not a satellite.
All other objects except satellites orbiting the sun shall be referred to collectively as Small Solar System Bodies (SSSB) (Messeri, 2010).
With the new definition, Pluto was demoted from the traditional nine (9) Planets and rebranded as a dwarf planet. The reclassification shows that the knowledge of the world around us is always changing (Wall, 2011). Pluto was first discovered in 1930 at the Lowell Observatory, Arizona (USA) by Clyde W Tombaugh (using a very powerful Telescope and mathematical calculation), and the search for Pluto by Tombaugh was based on the prediction of the existence of a planet.
Pluto is a celestial snowball with a surface of methane which is about 3.6 million miles from the sun. The debate that led to the demotion of Pluto started since the 1990s, when a group of scientist made a discovery of more than 1000 objects orbiting beyond Neptune (also called the Trans-Neptunian region). These bodies were around the domain of Pluto, which prompted some scientist to re-examine their basic understanding of the solar system structure.
Subsequently, new objects discovered were found to be more massive than Pluto, therefore if Pluto is a planet these objects should also be classified as Planets since they have satellites. Pluto failed on the third qualification since it has several dwarf planets around it. (See definition 1c). Pluto is now classified as dwarf planet alongside CERES, ERIS, HAUMEA, and MAKEMAKE, because it has not cleared the neighbourhood around its orbit. The planets include; MERCURY, VENUS, EARTH, MARS, JUPITER, SATURN, URANUS, NEPTUNE, which can be memorized using mnemonics, “ My Very Educated Mother Just Served Us Nachos or My Very Easy Method Just Simplified Using Names”.
Nine years after the IAU new planets definition Pluto’s Planethood still stirs controversy (Wall, 2011). As some scientist say Pluto should be back. They claim that the new definition is a flaw and unscientific.
Dr Alan Stern of the New Horizon  south east Research Institute said, “ the debate is on and it is wide ranging as we learn more and more about planetary types in our solar system and others”, he also said that the IAU have created a problem for themselves and for astronomy.
Owen Gingerich, a Harvard science historian (he chairs the IAU definition committee) in September 2014 argued that a planet is a culturally defined word that changes over time and that Pluto is planet. Some scientist also argue that the IAU’s effort is just to keep the number of planets down to a manageable size, which they consider an unworkable algorithm for deciding what’s a planet and what’s not.
Also, in Stern’s argument, he objects to the third criteria in the definition of a planet (1.c) which states that the planet must clear the neighbourhood around its orbit, he stressed that “ the further away a planet is from the sun, the bigger it needs to be to clear its zone and if the earth circled the sun in Pluto’s orbit, for example; it wouldn’t qualify for Planethood in the IAU’s eyes. He further said that, a river is a river, independent of whether there are rivers nearby, and in science things are called what they are base on their attributes not what they are next to.
But, William Gareth, Associate director of the IAU’s minor Planet Centre, said, Pluto is not a planet because it has several dwarf planets around it and also overlaps Neptune’s orbit at times. The next IAU general assembly is in Honolulu in August 2015, what’s next for Pluto is the question that we will expect an answer to. Meanwhile the NASA’s, New Horizon is sending a spacecraft to study Pluto up close to get more information on its status.
The debate is still on but officially there are currently eight (8) planets, five dwarf planets, and Pluto is a dwarf planet.
The public is not going to be excited by the fact that Pluto has been kicked out, but it is the right thing to do, (Britt, 2006), but this will put the layman in a state of confusion, because students in the secondary schools are still taught about the nine (9) planets in the solar system. This means that textbooks will of course be rewritten, as at the moment there is no change to that effect in the West African Examination Council (WAEC) and National Examination Council (NECO) syllabus for Geography. In 2006 WAEC (May/June) Examination marking scheme(Geography 1), the solar system was define as made up of the sun and its nine Planets with their satellite, also in NECO (June/July) Geography 1 the marking scheme define the solar system to consist of the sun and its nine planets with their satellites.
This implies that the NECO and WAEC syllabus for Geography still recognize Pluto as a planet and part of the solar system. There is however a need for an official statement from these examination bodies and other stakeholders on the status of Pluto in the solar system so as to avoid the confusion that might arise among teachers and students alike. This will go a long way to help teachers to focus on what to tell the students and what the students should write during international examinations or competitions.
The ongoing debate on the status of Pluto and the new definition of term planet in the solar system by the IAU is a welcome idea, as it stirs a lot of interest in research and scientific discovery. It is also an indication that teachers must be alert in order to brace up with changes in their various disciplines.
We also encourage Nigerian Astronomers and Planetary scientist to liaise with professional in the academic institutions to make this information available, so as not to confuse scholars.
Britt, R.R (2006). Pluto demoted: No longer a planet in a highly controversial definition.               Retrieved from
Messeri, L.R (2010). The problem with Pluto: conflicting cosmologies and classification                          of planets. Social studies of science. 40(2), 187-214.
Okoye, S.E (2006).  Astronomers’ solar system definition and the Pluto debate (I). The                     Guardian Newspaper; September, 7, 2006.
Rice, D (2014, October, 2). Wait, what? Pluto a planet again? [Weblogpost]. Retrieved                     from
Tytell, D (2005). The kings of the kuiper belt. Sky and Telescope.110 (10), 28.
Wall, M (2011, August, 24). Five years later, Pluto’s planethood definition still stirs                     controversy. [Weblogpost]. Retrieved from 

  Charles K Bijimi




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