Persephone
Persephone, also known in previous centuries as Planet 9, is an icy body ten times the mass of Earth and the furthest planet from the Sun in the Sol system.
Because of its distance from the Sun, Persephone was not detected for many centuries. However, the effects of its gravity were detected in the orbits of several distant celestial bodies, called extreme Kuiper Belt objects. As a result, Persephone was inferred to exist - in some theories as Planet 9[1] - before being definitively discovered.
Perspehone orbits the Sun once every 15,000 years. It is about 480,000 light-seconds from the Sun, and its surface temperature is 20 K (-253°C, -423°F).
Notes
- The ninth planet Persephone (Planet Nine, sometimes Planet X) was first suggested scientifically in 2014. It was not actually definitively discovered in real life yet.[1]
- This planet does not represent Planet X proposed by Percival Lowell in 1906 and now disapproved, but Planet Nine proposed by Chadwick A. Trujillo and Scott S. Sheppard, and further elaborated by Konstantin Batygin and Michael E. Brown.[1]