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Discovery of 'Goblin' Solar System Object Bolsters the Case For Planet Nine (gizmodo.com)
Astronomers have discovered a dwarf planet, dubbed "the Goblin," in the outer reaches of the Solar System that never gets any closer to the Sun than 6 billion miles. Some experts say its orbital configuration points to the existence of Planet Nine, a hypothetical planet in our Solar System that is estimated to be about 10 times the mass of Earth. Gizmodo reports: The Goblin, or 2015 TG38 as it's more formally called, is what's known as an extreme trans-Neptunian object, or ETNO. As the moniker implies, these objects, of which there are potentially thousands, are located well beyond the orbit of Neptune. The researchers who discovered the object, a team led by Scott Sheppard from the Carnegie Institution for Science and Chadwick Trujillo from Northern Arizona University, estimate that the Goblin is around 185 miles (300 kilometers) in diameter. At this size, it could very well be sphere-like in shape. Its mean distance from the Sun is about 80 astronomical units (AU), where 1 AU is the average distance from the Earth to the Sun. That's 7.45 billion miles, or 12 billion kilometers.
The Goblin's extreme orbital path means it never comes close enough to impose gravitational influence on the Solar System's giant planets, like Neptune or Jupiter. And at the astounding distance of 2,300 AU, it gets slotted into an emerging astronomical category known as Inner Oort Cloud objects (IOCs), of which 2012 VP113 and Sedna are the only other two known members. [...] The discovery of 2015 TG38 is bolstering the case for Planet Nine -- a hypothetical planet, sometimes referred to as Planet X, that's allegedly several times larger than Earth and located hundreds of AU away. As noted in the new study, published today in The Astronomical Journal, the location of Goblin's perihelion is similar to what's observed with Sedna and 2012 VP113, along with other ETNOs. This is a clue to astronomers that something potentially big, i.e. a super-Earth, is pushing these objects into similar types of orbits.
The Goblin's extreme orbital path means it never comes close enough to impose gravitational influence on the Solar System's giant planets, like Neptune or Jupiter. And at the astounding distance of 2,300 AU, it gets slotted into an emerging astronomical category known as Inner Oort Cloud objects (IOCs), of which 2012 VP113 and Sedna are the only other two known members. [...] The discovery of 2015 TG38 is bolstering the case for Planet Nine -- a hypothetical planet, sometimes referred to as Planet X, that's allegedly several times larger than Earth and located hundreds of AU away. As noted in the new study, published today in The Astronomical Journal, the location of Goblin's perihelion is similar to what's observed with Sedna and 2012 VP113, along with other ETNOs. This is a clue to astronomers that something potentially big, i.e. a super-Earth, is pushing these objects into similar types of orbits.
If you count everything as a planet, Pluto is not the ninth, there is a lot more. Wikipedia's list of minor plants has 523584 entries today.
Pluto isn't even the only thing once considered a planet that got "downgraded" to dwarf-plant. It happened to Ceres in the 1850s before. Ceres was discovered on the 1st of January 1801, far earlier than Pluto. Its orbit between those of Mars and Jupiter and it is far bigger than Goblin.
You've misread. Goblin's not the one that's several times larger than Earth -- Goblin is the 300km one. The fact that Goblin's orbit is where it is, is more evidence pointing to an as-yet unobserved hypothetical planet further out, Planet Nine, that is several times larger than Earth.