Yale University

Unexpected planets beyond Pluto: their discovery, physical properties, and implications for solar system history

Abstract: Recently, we discovered a body larger than Pluto at 100 times the Earth's distance from the sun using Yale's Palomar-QUEST camera. Officially designated 2003 UB313 (but nicknamed "Xena"), this new body is now the furthest known object in the solar system and the largest known body beyond Neptune. It is the largest body seen in the solar system since the discovery of Neptune in 1846. Along with Sedna, and several other Pluto-sized bodies we recently found with Palomar-QUEST, these bodies are the likely remnants of a sea of planetisimals that led to the growth of Uranus and Neptune in the outer solar system. In this talk I will discuss their unique physical properties - highly inclined orbits, surfaces covered with frozen methane, rotationally distorted shapes, and the existence of small moons in orbits around them. I will also discuss how their size and orbit distributions set important constraints on the primordial mass distribution of the solar system. In particular, the new bodies may be the initial detection of a remnant population of large planetesimals that were dispersed by encounters with Uranus and Neptune early in the formation of the solar system.

Additional searches may yield even larger bodies at even greater distances.

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