All the authors are science team members on the New Horizons mission to Pluto, operated for NASA by the John Hopkins University Applied Physics Laboratory. But now, Kirby Runyon, a doctoral student at Johns Hopkins University, thinks it's time to cancel that demotion and restore it as our Solar System's ninth planet. However, this information was tweaked in 2006, when Pluto was demoted from its former position of a planet to a dwarf planet.
There are now four recognized dwarf planets in the solar system other than Pluto, but NASA suspects there could be over 100 such objects that haven't yet been discovered.
Consequently Runyon and colleagues want to define a planet as "a sub-stellar mass body that has never undergone nuclear fusion" and that has enough gravitational heft to maintain a roughly round shape. Earth's moon was considered a planet by ancient astronomers, and has several unusual features that set it apart from other moons in the solar system. Dwarf planets like Pluto and Eris, moons like Ganymede and Titan (satellites of Jupiter and Saturn respectively that outsize Mercury, ) all the way down to mighty Mimas, a moon of Saturn with a smaller surface area than Spain, would all be included. "In the decade following the supposed "demotion" of Pluto by the [IAU], many members of the public, in our experience, assume that alleged "non-planets" cease to be interesting enough to warrant scientific exploration, though the IAU did not intend this effect", wrote Stern.
These smaller planets, which now famously includes Pluto, are located in a region beyond the icy planet known as the Kuiper Belt.
There has been lot of arguments and debates related to accepting Pluto as a planet.
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The team of researchers suggested a new definition of a planet in a February proposal, that is more in line with "scientific classification and peoples' intuition'" should be adopted.
But, based on that last aspect it could be reasoned that the IAU definition also excludes Earth, Mars, Jupiter and Neptune too, as they share their orbits with asteroids.
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. The decision left the solar system with eight planets. His proposal eradicates the main element of the International Astronomical Union's definition of a planet, which is what initially demoted Pluto to a dwarf planet in 2006. Majority are closely affiliated with geology and other geosciences, thus making the new geophysical definition more useful than the IAU's astronomical definition, they said.
That expansion is part of the appeal of the new definition, Runyon says.