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B. W. Jones, D. R. Underwood, P. N. Sleep (The Open University, UK)
We have carried out lengthy investigations of seven exoplanetary systems, to obtain an estimate of the distance D from the giant planet in each system within which orbital stability is unlikely for a planet of order of Earth mass (EMP). Distances less than D define the disaster zone. For orbits interior (alternatively exterior) to the giant orbit, D is measured from the giant periastron (alternatively apastron) and is a multiple n(int) (alternatively n(ext)) of the giant Hill radius, where n(int) and n(ext) depend on the giant orbital eccentricity. We have estimated n(int) and n(ext) for each of the seven systems by launching an EMP in various orbits and following their long term fate with a hybrid orbital integrator. We thus establish empirical functions for n(int) and n(ext) versus the orbital eccentricity of the giant. For any exoplanetary system we can now obtain the extent of the disaster zone around each giant. We can then compare the disaster zones with the habitable zone (HZ) of the exoplanetary system, and from the extent of any overlap establish whether confinement of an EMP anywhere in the HZ is likely. Systems where it is likely should have high priority in searches for habitable EMPs.
The HZ migrates outwards as the star evolves, and therefore the overlap varies with time. By using a model of stellar evolution we have established for how long any confinement could extend from today into the past. We have also examined the duration of any confinement that becomes possible sometime during the main-sequence lifetime. In this way we have shown that about half of the presently known exoplanetary systems offer confinement for at least 1000 Myr into the immediate past, and that about two thirds do so for at least 1000 Myr at some time during the main sequence lifetime.
The author(s) of this abstract have provided an email address for comments about the abstract: b.w.jones@open.ac.uk
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.