Planet Nine estimated mass of ten Earths, a diameter two to four times that of Earth, and an elongated orbit lasting 10,000 - 20,000 years. Batygin and Brown suggest that Planet Nine could be the core of a primordial giant planet that was ejected from its original orbit by Jupiter during the genesis of the Solar System. Others have proposed that the planet was captured from another star, is a captured rogue planet, or that it formed on a distant orbit and was pulled into an eccentric orbit by a passing star. As of 2018, efforts have failed to directly observe Planet
Planet V Sun after entering the ν secular resonance. As an initial test of the Planet V hypothesis, Chambers and Lissauer conducted 36 computer simulations of the Solar System with an additional terrestrial planet. A variety of parameters were used to determine the impacts of Planet V's initial orbit and mass. The mean time at which Planet V was lost was found to increase from 100 Myr to 400 Myr as its initial semi-major axis was increased from 1.8 to 1.9 AU. Results consistent with the current Solar System were most common with a 0.25 Mars mass Planet V. In cases with