A pair of astrophysicists, one with Kindai University, the other the National Astronomical Observatory of Japan, both in Japan, have found possible evidence of an Earth-like planet residing in the Kuiper Belt. In their paper published in The Astronomical Journal, Patryk Sofia Lykawka and Takashi Ito describe properties of the Kuiper Belt that they believe are consistent with the existence of a planet not much bigger than Earth.
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Source: Phys.org