In an article published in the Astronomical Journal on Wednesday, planetary scientists Konstantin Batygin and Mike Brown from the California Institute of Technology (Caltech) announced that though the Planet Nine still has not been observed directly, strong evidence based on mathematical modeling and computer simulations clearly suggest that it really exists far beyond the dwarf planet Pluto.
According to the findings, the new family member has a mass of about ten times that of the Earth, orbits about 20 times farther from the Sun than Neptune (which revolves round the Sun at an average distance of about 4.5 billion kilometers (2.8 billion miles)), and takes between 10,000 and 20,000 Earthly years to circle our star.
“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we become increasingly convinced that it is out there. For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete,” said Batygin.
Pluto was considered as the ninth planet of the Solar System until 2006. In August of that year, however, the International Astronomical Union purposed a new definition of planet and excluded Pluto from the planetary family of the solar system since the trans-Neptunian object could not fit the definition. The landmark decision reclassified Pluto under the new “dwarf planet” category.
According to the new definition, three criteria must be met to call a celestial body a planet: orbiting around the Sun, having a sufficient mass to assume hydrostatic equilibrium (a nearly spherical shape), and having cleared the neighborhood around its orbit. Clearing the neighborhood around the orbit means that the planet must be gravitationally dominant in its orbit, without any other bodies of comparable size other than its own satellites or those otherwise under its gravitational influence. If a planet has not cleared its neighborhood, it is classified as a dwarf planet.