Back in January, ‘Pluto killing’ astronomer Mike Brown announced that he and his colleagues had found evidence that a massive, icy planet could be lurking on the edge of the Solar System, just past Neptune, about 149 billion km from the Sun.
No one’s ever seen it (being 75 times more distant than Pluto doesn’t help), but Brown’s estimated that the hypothetical ‘Planet Nine’ orbits our Sun every 10,000 to 20,000 years, and is about 10 times more massive than Earth and four times the size.
Now, Swiss astronomers have used the available data surrounding Planet Nine to figure out what the upper and lower limits on how big, bright, and warm it could actually be. The evidence suggests it’s like a ‘mini-Uranus’, with a solid iron core surrounded in ice and a dense layer of gas. Source: Astrophysicists have predicted what Planet Nine would be made of