It's also big. Its basically a smaller version of Uranus and Neptune -- a small ice giant with an envelope of hydrogen and helium. It's been calculated to be equal to 3.7 Earth radii. The Earth's radius, the distance from the core to the surface, is a little under 4000 miles. That means Planet 9 is almost 30,000 miles across. In other words if you were to drive nonstop, 24 hours a day at 70mph, it would take you nearly 40 days to get back to where you started while only taking about 15 days to circumnavigate the Earth.
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