Delay of planet formation at large radius and the outward decrease in mass and gas content of Jovian planets

作     者：Li-Ping Jin Chun-Jian Liu Yu Zhang 

作者机构：College of Physics Jilin University 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2015年第15卷第9期

页      面：1597-1603页

核心收录：

学科分类：07[理学] 08[工学] 070401[理学-天体物理] 0835[工学-软件工程] 0802[工学-机械工程] 0704[理学-天文学] 080201[工学-机械制造及其自动化] 

基　　金：supported in part by the National Natural Science Foundation of China (NSFC, Grant Nos. 11073009, 10873006, 11373019 and 10573007) by three grants from Jilin University 

主　　题：planetary systems    planets and satellites: formation    planets and satellites: gaseous planets    planets and satellites: individual (Jovian planets)    protoplanetary disks 

摘      要：A prominent observation of the solar system is that the mass and gas content of Jovian planets decrease outward with orbital radius, except that, in terms of these properties, Neptune is almost the same as Uranus. In previous studies, the solar nebula was assumed to preexist and the formation process of the solar nebula was not considered. It was therefore assumed that planet formation at different radii started at the same time in the solar nebula. We show that planet formation at different radii does not start at the same time and is delayed at large radii. We suggest that this delay might be one of the factors that causes the outward decrease in the masses of Jovian planets. The nebula starts to form from its inner part because of the inside-out collapse of its progenitorial molecular cloud core. The nebula then expands outward due to viscosity. Material first reaches a small radius and then reaches a larger radius, so planet formation is delayed at the large radius. The later the material reaches a planet＇s location, the less time it has to gain mass and gas content. Hence, the delay tends to cause the outward decrease in mass and gas content of Jovian planets. Our nebula model shows that the material reaches Jupiter, Saturn, Uranus and Neptune at t = 0.40, 0.57, 1.50 and 6.29 × 10^6 yr, respectively. We discuss the effects of time delay on the masses of Jovian planets in the framework of the core accretion model of planet formation. Saturn＇s formation is not delayed by much time relative to Jupiter so that they both reach the rapid gas accretion phase and become gas giants. However, the delay in formation of Uranus and Neptune is long and might be one of the factors that cause them not to reach the rapid gas accretion phase before the gas nebula is dispersed. Saturn has less time to go through the rapid gas accretion, so Saturn＇s mass and gas content are significantly less than those of Jupiter.