Why is Pluto nowadays called a drawf planet?

Asked on by viswanth

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readerofbooks's profile pic

readerofbooks | College Teacher | (Level 2) Educator Emeritus

Posted on

This is a good question. It is probably best to start with a definition of what a dwarf planet is and then discuss whether Pluto is a dwarf planet.

According to the International Astronomical Union (IAU), dwarf plants are a spherical body that orbits the sun, which has a large enough mass to have its own gravitational pull, but not  large enough gravitational of a pull that it clears its region of planetesimals.

Based on this definition, people debate whether Pluto is a dwarf planet or not. There is still a debate going on now. Some argue that Pluto is a dwarf plaent; other still argue that Pluto is a planet.


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plutosavior | Student, Undergraduate | eNotes Newbie

Posted on

Dwarf planets are planets too, in spite of the controversial 2006 vote by four percent of the International Astronomical Union. Dr. Alan Stern coined the term "dwarf planet" in 1991 to refer to a third class of planets in addition to terrestrials and jovians, small planets that are large enough to be rounded by their own gravity but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all. The real issue at hand is two different ways of viewing the solar system. Dynamicists focus on the effects a celestial body has on neighboring bodies; therefore, to them, a celestial body has to gravitationally dominate its orbit in order to be considered a planet. The primary focus is on where the body is. Geophysicists, in contrast, focus not on the effects a celestial body has on other celestial bodies, but on individual celestial bodies themselves, their composition and structure. To geophysicists, a celestial body is a planet if it orbits a star and is large enough to be squeezed into a round shape by its own gravity, a state known as hydrostatic equilibrium. Interestingly, hundreds of professional astronomers signed a formal petition rejecting the IAU decision. The notion that dwarf planets are a subclass of planets is consistent with the use of the term "dwarf" in astronomy, where dwarf stars are a subclass of stars, and dwarf galaxies are a subclass of galaxies.

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