Earth-Mass Planets in Tandem Disks

Abstract

This paper presents a new terrestrial planet formation theory demonstrating that Earth-mass planets form naturally in tandem protosolar disks. Our model builds upon tandem planet formation theory (Ebisuzaki and Imaeda 2017; Imaeda and Ebisuzaki 2017a,b, 2018), incorporating magneto-rotational instability (MRI) suppression (Balbus and Hawley 1991; Hawley and Balbus 1991), porous particle aggregation (Okuzumi et al. 2012; Kataoka et al. 2013), and standard planet formation mechanisms (e.g., Safronov 1969; Hayashi et al. 1985). In a tandem proto-solar disk, planets form at two distinct locations: the inner and outer edges of the MRI-suppressed region, where solid particles accumulate. The inner edge produces rocky planets, while the outer edge forms gas giants. When planetesimals reach Earth-sized mass at the inner MRI edge, they migrate outward due to gas disk torque. For a protosolar disk accretion rate of M_dot = 10^-7.08 solar masses per year (Case D), the total solid mass at the inner MRI edge reaches 1.99 Earth masses, producing two Earth-mass planets. This result closely matches the solar system's terrestrial planet distribution (Earth and Venus), which comprises 92% of total terrestrial planet mass, providing strong support for our formation mechanism.