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Planet V
Planet V is a hypothetical fifth terrestrial planet posited by NASA scientists John Chambers and Jack J. Lissauer to have once existed between Mars and the asteroid belt. In their hypothesis the Late Heavy Bombardment of the Hadean era began after perturbations from the other terrestrial planets caused Planet V’s orbit to cross into the asteroid belt. Chambers and Lissauer presented the results of initial tests of this hypothesis during the 33rd Lunar and Planetary Science Conference, held from March 11 through 15, 2002.〔Space.com: "Long-Destroyed Fifth Planet May Have Caused Lunar Cataclysm, Researchers Say"〕
==Hypothesis==
In the Planet V hypothesis five terrestrial planets were produced during the planetary formation era. The fifth terrestrial planet began on a low-eccentricity orbit between Mars and the asteroid belt with a semi-major axis between 1.8 and 1.9 AU. While long-lived, this orbit was unstable on a time-scale of 600 Myr. Eventually perturbations from the other inner planets drove Planet V onto a high-eccentricity orbit which crossed into the inner asteroid belt. Asteroids were scattered onto Mars-crossing and resonant orbits by close encounters with Planet V. Many of these asteroids then evolved onto Earth-crossing orbits temporarily enhancing the lunar impact rate. This process continued until Planet V was lost most likely by impacting the Sun after entering the ν6 secular resonance.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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