... Credit: M. Brown ( Caltech ), C. Trujillo ( Gemini ), D. Rabinowitz ( Yale ), NSF , NASA Explanation: Is that a tenth planet? A faint, slowly moving dot discovered by computer shows clear signs of being a deep Solar System object at least as large as Pluto . The object, designated 2003 UB 313 , is currently situated nearly 100 times the Earth-Sun distance -- over twice the average Pluto-Sun distance. ... Since 2003 UB 313 is surely not completely reflective , it could be substantially larger. ...