A group of members of the New Horizons mission to Pluto are making the case to redefine what constitutes as a planet to be more inclusive.
The matter will be debated at the upcoming Lunar and Planetary Science Conference in Houston, but Fazekas does not think there will be much headway made in changing the current definition of a planet or changing the status of Pluto as a dwarf planet. Back in 2006 that all changed, when Pluto was demoted from being labeled a proper planet to its new classification as a dwarf planet, leaving just eight true planets in our celestial neighborhood.
It is claimed that after the acceptance of this definition, numerous unidentified objects revolving the solar system would be termed as planets.
According to Runyon and his team members a planet can be defined as "a sub stellar mass body that has never undergone any kind of nuclear fusion" which have enough gravitational mass in order to maintain roughly a round shape. And if Runyon and the other people on the team he leads are successful, our Solar System would have more than 100 planets, including many bodies we now call moons. 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. There is, in fact, nothing so non-planet about Pluto, adds Runyon. Still, Pluto "has everything going on on its surface that you associate with a planet". Pluto was smallest of the nine planets and its diameter being under three-quarters of the moon and approximately a fifth of the Earth.
Ancient and medieval astronomers believed the moon to be a planet, as common wisdom of the time proposed that the Earth was the center of the universe and all objects revolved around it. The decision left the solar system with eight planets.
This definition differs from the three-element IAU definition in that it makes no reference to the celestial body's surroundings. 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. Most planetary scientists are also generally trained as geoscientists more than astrologists, so a geophysical definition might suit them better than the old classification.
Additional authors of the paper are from the Southwest Research Institute, the National Optical Astronomy Observatory, the Lowell Observatory, and George Mason University.