If found, the giant world would represent the first discovery of a planet in our solar system since Pluto in 1930, and before that Neptune in 1846. (Pluto was subsequently downgraded from planet to “dwarf planet” in 2006.) It is this hypothetical planet – known as Planet Nine – that Becker used in her analysis. Uranus, a gas giant planet, is the next largest planet, at 14.5 times Earth’s mass. A gaseous planet will be less dense and therefore larger than a rocky or predominantly metallic world.

Source: The Guardian May 23, 2018 05:26 UTC