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Project Progress

Study of habitability and water-delivery in binary star systems requires an expansive study of the dynamical evolution of these systems. While habitability requires identifying regions within the habitable zone of the system where a life-harboring planet (such as an Earth-size body) can have a long-term stable orbit, water-delivery requires identifying regions where water-carrying objects such as comets, and water-rich planetesimals and protoplanets, can be unstable. Together these two issues require a detailed and thorough study of the dynamical stability of the binary-planetary system. A vast and systematic study of the formation and stability of planets has begun during this year, both giant and terrestrial, in binary star systems. The motivation behind this study comes from the fact that among more than 150 extrasolar planets discovered to date, approximately 25% are within binary star systems. Some of such systems (e.g., Gamma Cephei), have small separations and also harbor planets — a phenomenon that is not allowed based on the current theories of planet formation. The present research on this topic has been focused on the long-term stability of planets in the binary star system of Gamma Cephei. This system consists of a 1.6 solar-mass star as its primary, an M dwarf, at a distance of 19 AU, as its secondary, and a Jupiter-like planet that revolves around the primary star at 2.1 AU. To study the habitability of this system, the entire parameter-space of this system has been mapped and this shows that the system can, indeed, be habitable as long as the binary eccentricity stays below 0.45 (Figure 1). The results of this project have been submitted for publication in the Astrophysical Journal. Currently, calculations are being expanded to include interactions among planetesimals at different locations in the binary in order to understand the formation of terrestrial planets in that system.

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