A low mass for Mars from Jupiter's early gas-driven migration

摘要

巨型行星在太阳系生命中形成的时间要比陆地rn行星早得多，它们只花了几百万年时间就从原rn始行星盘形成了。它们在10万年的时间尺度上rn移动性也很强。现在，对早期太阳系所做模拟，rn显示了木星在一次向外的迁移之后所发生的一rn次向内的迁移何以能够产生一个被截去一部分rn的“星子盘”，陆地行星就是在之后的3,000万rn～5,000万年间从这个“星子盘”形成的。陆地rn行星是在很晚之后才停止吸积的，而如果说这rn些行星是由一个外沿距太阳约一个天文单位的rn“星子盘”形成的话，那么它们的特点(包括rn火星较小的质量)便能够得到最好的重现。%Jupiter and Saturn formed in a few million years (ref. 1) from a gas-dominated protoplanetary disk, and were susceptible to gas-driven migration of their orbits on timescales of only ~ 100,000 years (ref. 2). Hydrodynamic simulations show that these giant planets can undergo a two-stage, inward-then-outward, migration3"5. The terrestrial planets finished accreting much later6, and their characteristics, including Mars' small mass, are best reproduced by starting from a planetesimal disk with an outer edge at about one astronomical unit from the Sun73 (1 au is the Earth-Sun distance). Here we report simulations of the early Solar System that show how the inward migration of Jupiter to 1.5 au, and its subsequent outward migration, lead to a planetesimal disk truncated at 1 au; the terrestrial planets then form from this disk over the next 30-50 million years, with an Earth/Mars mass ratio consistent with observations. Scattering by Jupiter initially empties but then repopulates the asteroid belt, with inner-belt bodies originating between 1 and 3 au and outer-belt bodies originating between and beyond the giant planets. This explains the significant compositional differences across the asteroid belt. The key aspect missing from previous models of terrestrial planet formation is the substantial radial migration of the giant planets, which suggests that their behaviour is more similar to that inferred for extrasolar planets than previously thought.