We present a new theoretical analysis of the PSR B1620 - 26 triple system in the globular cluster M4 , based on the latest radio pulsar timing data , which now include measurements of five time derivatives of the pulse frequency .
These data allow us to determine the mass and orbital parameters of the second companion completely ( up to the usual unknown orbital inclination angle i _ { 2 } ) .
The current best-fit parameters correspond to a second companion of planetary mass , m _ { 2 } \sin i _ { 2 } \simeq 7 \times 10 ^ { -3 } M _ { \odot } , in an orbit of eccentricity e _ { 2 } \simeq 0.45 and semimajor axis a _ { 2 } \simeq 60 AU .
Using numerical scattering experiments , we study a possible formation scenario for the triple system , which involves a dynamical exchange interaction between the binary pulsar and a primordial star–planet system .
The current orbital parameters of the triple are consistent with such a dynamical origin , and suggest that the separation of the parent star–planet system was very large , \mathrel { \raise 1.29 pt \hbox { $ > $ } \mkern - 14.0 mu \lower 2.58 pt \hbox { $ \sim$ } } 50 AU .
We also examine the possible origin of the anomalously high eccentricity of the inner binary pulsar .
While this eccentricity could have been induced during the same dynamical interaction that created the triple , we find that it could equally well arise from long-term secular perturbation effects in the triple , combining the general relativistic precession of the inner orbit with the Newtonian gravitational perturbation of the planet .
The detection of a planet in this system may be taken as evidence that large numbers of extrasolar planetary systems , not unlike those discovered recently in the solar neighborhood , also exist in old star clusters .