* Astronomy

Could the 47 UMa Planetary System be a Second Solar System: predicting the Earth-like planets.
Authors: Jianghui Ji , Lin Liu , H. Kino****a , Guangyu Li (Purple Mountain Observatory, Nanjing University, NAOC, NAOJ)



(Abridged)
Researchers have numerically investigated the dynamical architecture of 47 Ursa Major with the planetary configuration of the best-fit orbital solutions by Fischer et al. They systematically studied the existence of Earth-like planets in the region 0.05 AU ≤ a ≤ 2.0 AU for 47 Ursa Major with numerical simulations, and also explored the packed planetary geometry and Trojan planets in the system.
In the simulations, they found that "hot Earths" at 0.05 AU ≤ a ≤ 0.4 AU can dynamically survive at least for 1 Million years. The Earth-like planets can eventually remain in the system for 10 Million years in areas involved in the mean motion resonances (MMR) (e.g., 3:2 MMR) with the inner companion.
Moreover, they showed that the 2:1 and 3:1 resonances are on the fringe of stability, while the 5:2 MMR is unstable. Additionally, the 2:1 MMR marks out a remarkable boundary between chaotic and regular motions, inside, most of the orbits can survive, outside, they are mostly lost in the orbital evolution.
In a dynamical sense, the most likely candidate for habitable environment is Earth-like planets with orbits in the ranges 0.8 AU ≤ a ≤ 1.0 AU and 1.0 AU ≤ a ≤ 1.30 AU (except several unstable cases) with relatively low eccentricities.
The Trojan planets with low eccentricities and inclinations can secularly last at the triangular equilibrium points of two massive planets. Hence, the 47 UMa planetary system may be a close analogy to our solar system.



The main sequence star 47 Ursa Major (HD 95128 ) is of spectral type G0 V with a mass of 1.03 solar masses. Butler & Marcy (1996) reported the discovery of the first planet in the 47 UMa system which has become one of the most eye-catching systems particularly after the subsequent discovery of an additional companion.

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Parameter      Companion B Companion C
Msini(MJup)     2.86       1.09
Orbital period  1079.2     2845.0
a(AU)           2.077      3.968
Eccentricity e  0.05       0.00
!(deg)          124.3      170.89
Periastron Time 2452374.1  2448750.9

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