The Dynamical Architecture and Habitable Zones of the Quintuplet Planetary System 55 Cancri

arXiv:0902.4328v1 [astro-ph.EP] 25 Feb 2009 Chin. J. Astron. Astrophys. Vol.0 (2008) No.2, 000–000 (http://www.chjaa.org ) Chinese Journal of Astronomy and Astrophysics The Dynamical Architecture and Habitable zones of the Quintuplet Planetary System 55 Cancri Jianghui JI1,2 ⋆, Hiroshi Kinoshita3, Lin LIU4 and Guangyu LI1,2 1 Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China 2 National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China 3 National Astronomical Observatory, Mitaka, Tokyo 181-8588, Japan 4 Department of Astronomy, Nanjing University, Nanjing 210093, China Received 2008/09/08 Abstract We perform numerical simulations to study the secular orbital evolu- tion and dynamical structure in the quintuplet planetary system 55 Cancri with the self-consistent orbital solutions by Fischer and coworkers (2008). In the simu- lations, we show that this system can be stable at least for 108 yr. In addition, we extensively investigate the planetary configuration of four outer companions with one terrestrial planet in the wide region of 0.790 AU ≤a ≤5.900 AU to examine the existence of potential asteroid structure and Habitable Zones (HZs). We show that there are unstable regions for the orbits about 4:1, 3:1 and 5:2 mean motion resonances (MMRs) with the outermost planet in the system, and several stable orbits can remain at 3:2 and 1:1 MMRs, which is resemblance to the asteroidal belt in solar system. In a dynamical point, the proper candidate HZs for the existence of more potential terrestrial planets reside in the wide area between 1.0 AU and 2.3 AU for relatively low eccentricities. Key words: celestial mechanics-methods:n-body simulations-planetary systems- stars:individual(55 Cancri) 1 INTRODUCTION The nearby star 55 Cancri is of spectral type K0/G8V with a mass of 0.92 ± 0.05M⊙(Valenti & Fischer 2005). Marcy et al. (2002) reported a second giant planet with a long period of ∼14 yr after the first planet discovered in 1997. The 55 Cnc system can be very attractive, because first it hosts a distant giant Jupiter-like planet about 5.5 AU resembling Jupiter in our solar system. The second interesting thing is that this system may be the only known planetary system in which two giant planets are close to the 3:1 orbital resonance, and the researchers have extensively studied the dynamics and formation of the 3:1 MMR in this system (see ⋆E-mail: jijh@pmo.ac.cn 2 Jianghui JI et al. Beaug´e et al. 2003; Ji et al. 2003; Zhou et al. 2004; Kley, Peitz, & Bryden 2004; Voyatzis & Hadjidemetriou 2006; Voyatzis 2008). Still, the additional collection of follow-up observations and the increasing of precision of measurements (at present ∼1 ms−1 to 3 ms−1) have indeed identified more planets. McArthur et al. (2004) reported the fourth planet with a small minimum mass ∼14 M⊕that orbits the host star with a short period of 2.8 day, by analyzing three sets of radial velocities. The improvement of the observations will actually induce additional discovery. Hence, it is not difficult to understand that more multiple planetary systems or additional planets in the multiple systems are to be dug out supplemental data. More recently, Fischer et al. (2008) (hereafter Paper I) reported the fifth planet in the 55 Cnc system with the Doppler shift observations over 18 yrs, and showed that all five planets are in nearly circular orbits and four have eccentricities under 0.10. It is really one of the most extreme goals for the astronomers devoted to searching for the extrasolar planets to discover a true solar system analog, which may hold one or two gas giants orbiting beyond 4 AU that can be compared to Jupiter and Saturn in our own solar system (Butler 2007, private communication; see also Gaudi et al. 2008). This indicates that several terrestrial planets may move in the so- called Habitable Zones (HZs) (Kasting et al. 1993; Jones et al. 2005), and the potential asteroidal structure can exist. Considering the probability of the coplanarity and nearly circular orbits for five planets (Paper I), the 55 Cnc system is suggested to be a comparable twin of the solar system. Hence, firstly, in a dynamical viewpoint, one may be concerned about the stability of the system over secular timescale. On the other hand, the small bodies as terrestrial objects may exist in this system and are to be detected with forthcoming space-based missions (Kepler, SIM ). In this paper, we focus on understanding the dynamical structure and finding out suitable HZs for life-bearing terrestrial planets in this system. 2 DYNAMICAL ANALYSIS In this paper, we adopt the orbital parameters of the 55 Cancri system provided by Paper I (see their Table 4). For the convenience of narration, we re-label the planets according to the ascendant semi-major axes in the order from the innermost to the outermost planet (e.g., B, C, D, E, F), while the original names discovered in the chronological order are also accompanied but i

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