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Project Progress

To understand the possibility of the existence of habitable planets in multi-planet systems, numerical integrations were carried out to identify the regions of stability of Earth-like objects in the systems of ? Andromedae (HZ=1.68-2 AU), 47 UMa (HZ=1.16-1.41 AU), GJ 876 (HZ=0.1-0.13 AU), and 55 Cancri (HZ=0.72-0.87 AU). Figure 1 shows the graphs of the lifetimes of an Earth-like planet, at different distances from the central stars of these systems, for 10 Myr. Results show that
1) the stable orbit of the newly discovered Earth-like planet of GJ 876 is stable
2) the orbit of the small close-in planet of 55 Cnc, as reported by McArthur et al. (2004) is unstable,
3) it is unlikely that ? Andromedae and GJ 876 harbor habitable planets,
4) the two systems of 47 UMa and 55 Cnc have stable habitable zones, and
5) the 55 Cnc system is harboring stable planet(s) in the region between 0.7 AU and 2.2 AU. The newly discovered Neptune-sized planet of this system is located in this region.

To understand the effect of the perturbation of a stellar companion on the formation of habitable planets in binary stars systems, the late stage of terrestrial planet formation in such environments were simulated. Figure 2 shows some of the results for binary mass-ratios 0.5, 1.5. As shown here, it is possible to form Earth-like objects with substantial amount of water in the HZ of the primary star. The sizes of these planets and their water content vary with the semimajor axis and eccentricity of the stellar companion. Results indicate that Earth-like objects are formed in systems where the interaction between the giant planet and the secondary star is weak and the average eccentricity of the giant planet is small.

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