The so-called “Planet Nine,” as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. Here’s the order of the planets, starting nearest the sun and working outward through the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune — and Planet Nine.
The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one—it “has not cleared its neighboring region of other objects.”
While most science fiction calls our sun Sol, and our system the Sol System, the International Astronomical Union (IAU), the body authorized internationally to name stellar objects, calls it “the Solar System”, and our sun, “the Sun”.
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