Post-oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
Post-oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
复制标题
DOI：
10.1086/519918
复制
发表时间：
2007-05
期刊：
影响因子：
--
通讯作者：
Ji-lin Zhou;D. Lin;Yi-sui Sun
中科院分区：
文献类型：
--
作者：
Ji-lin Zhou;D. Lin;Yi-sui Sun
在连续吸积模型中，行星的形成是通过尘埃的沉积、微行星的凝聚碰撞以及在有效气体吸积开始之前原行星胚胎的凝聚。作为类地行星的祖先和气体巨行星的核心，胚胎具有相当的质量，并且在寡头生长后被其喂养区的全宽度分开。在这种情况下，我们调查的轨道交叉时间（Tc）的原行星系统具有相等的行星质量和初始分离k 0缩放的相互希尔半径（“EMS系统”）。在无气体环境中，log [Tc/（1 yr）]= log（k 0/2.3）+ B，其中A和B是行星质量和初始偏心率的函数。该幂律是由EMS系统中速度弥散σ（t）的随机游走扩散引起的。扩散还导致（1）在时间t处具有概率P（t）=（e/σ2）exp [-e2/（2σ2）]的偏心率的瑞利分布和（2）平均偏心率的演变Δ t 1/2。作为这种混沌扩散的证据，已知太阳系外行星的观测偏心率服从瑞利分布。在气态环境中，当胚胎分离良好（k 0 = 6-12）时，它们的轨道交叉趋势会被潮汐阻力抑制，并且它们的生长会随着轨道的圆化而停滞。我们评估的隔离质量的胚胎，这决定了气体巨星形成的概率，作为一个功能的灰尘和气体的表面密度。
In the sequential accretion model, planets form through the sedimentation of dust, cohesive collisions of planetesimals, and coagulation of protoplanetary embryos prior to the onset of efficient gas accretion. As progenitors of terrestrial planets and the cores of gas giant planets, embryos have comparable masses and are separated by the full width of their feeding zones after the oligarchic growth. Within this context, we investigate the orbit-crossing time (Tc) of protoplanetary systems with equal planetary masses and initial separation k0 scaled by their mutual Hill radii ("EMS systems"). In a gas-free environment, log [Tc/(1 yr)] ≃ A + B log (k0/2.3), where A and B are functions of the planetary masses and initial eccentricities. This power law is caused by a random-walk diffusion of velocity dispersion σ(t) in the EMS systems. The diffusion also leads to (1) a Rayleigh distribution of eccentricities with probability P(t) = (e/σ2) exp [-e2/(2σ2)] at time t and (2) an evolution of average eccentricity ∝t1/2. As evidence of this chaotic diffusion, the observed eccentricities of known extrasolar planets obey a Rayleigh distribution. In a gaseous environment, as embryos become well separated (with k0 ≃ 6-12), their orbit-crossing tendency is suppressed by tidal drag, and their growth is stalled as their orbits are circularized. We evaluate the isolation masses of the embryos, which determine the probability of gas giant formation, as a function of the dust and gas surface densities.