Following the notion that the Titius-Bode rule (TBR) may also be applicable
to some extra-solar planetary systems, although this number could be relatively
small, it is applied to 55 Cancri, which is a G-type main-sequence star
currently known to host five planets. Following a concise computational
process, we tentatively identify four new hypothetical planetary positions
given as 0.081, 0.41, 1.51 and 2.95 AU from the star. The likelihood that these
positions are occupied by real existing planets is significantly enhanced for
the positions of 1.51 and 2.95 AU in the view of previous simulations on planet
formation and planetary orbital stability. For example, Raymond et al. (2008)
[ApJ 689, 478] argued that additional planets would be possible between 55 Cnc
f and 55 Cnc d, which would include planets situated at 1.51 and 2.95 AU. If
two additional planets are assumed to exist between 55 Cnc f and 55 Cnc d, the
deduced domains of stability would be given as 1.3-1.6 and 2.2-3.3 AU. The
possible planet near 1.5 AU appears to be located at the outskirts of the
stellar habitable zone, which is however notably affected by the stellar
parameters as well as the adopted model of circumstellar habitability. We also
compute the distance of the next possible outer planet in the 55 Cnc system,
which if existing is predicted to be located between 10.9 and 12.2 AU, which is
consistent with orbital stability constraints. The inherent statistical
significance of the TBR is evaluated following the method by Lynch (2003)
[MNRAS 341, 1174]. Yet it is up to future planetary search missions to verify
or falsify the applicability of the TBR to the 55 Cnc system, and to attain
information on additional planets, if existing.Comment: 9 pages, 3 figures, 9 tables; accepted by Publications of the
Astronomical Society of Japan; to be published on 2012 August 25; Ref.: PASJ
64 (4
