23 March, 2017
A newer, more accurate definition of what is and what is not a planet is needed.
In 2006, the International Astronomical Union dropped Pluto from the list of planets in our solar system, bringing the number down to eight.
But now, in a bid to regain Pluto's lost status and adding new planets to our solar system, the researcher team from Johns Hopkins University has come up with the clarification of the definition of the planet, approved by IAU in 2006.
Runyon himself is of the opinion that the very word "planet" carries a "psychological weight" and that a debate might engage public interest. The six-member team led by scientist Kirby Runyon are pitching to have 100 celestial bodies categorised as planets. According to Runyon, a planet is, "a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters". More than 10 years later, some scientists want Pluto to get its old title back. These dark and light regions form because portions of Pluto's atmosphere periodically collapse, with air freezing and falling onto the dwarf planet's surface, he and colleagues suggest.
That definition change meant Pluto was no longer considered the "ninth" planet, but instead a dwarf planet and Kuiper Belt Object.
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Every discovered planet in the Solar System under 10,000 km in diameter, to scale. Other bodies such as satellite of Jupiter, Europa would also come under the ambit of this definition. Among the paper's co-authors is New Horizons principal investigator S. Alan Stern, who has argued in the past that the IAU's current definition is inadequate, as the zone-clearing requirement that booted Pluto technically also excludes planets that share their orbits with asteroids, such as Mars, Jupiter, Neptune, and even Earth.
At present, the IAU's definition of what makes a planet a planet states that a body must orbit the Sun, it must be massive enough for its own gravity and it requires that the body has "cleared the neighborhood" around its orbit, meaning it has become gravitationally dominant.
This definition is different from the three-element IAU definition in a way the there has been no reference made to the celestial body surroundings.
Astronomers "may find the IAU definition perfectly useful", but "our geophysical definition is more useful for planetary geoscience practitioners, educators and students". That expansion is part of the appeal of the new definition, said Runyon.
The other authors are Kelsi Singer of the Southwest Research Institute in Boulder, Colorado; Tod Lauer of the National Optical Astronomy Observatory in Tucson, Arizona; Will Grundy of the Lowell Observatory in Flagstaff, Arizona; Michael Summers of George Mason University in Fairfax, Virginia.