Possible Detection of a Planet Orbiting the Geminga Gamma-Ray Pulsar

A new analysis of gamma-ray arrival times using both recent EGRET/CGRO exposure and the archival COS-B exposure yields a cubic ephemeris which predicts the rotational phase of Geminga with errors smaller than 50 milliperiods for all high-energy gamma-ray observations which span a 24 year timing baseline. Timing residuals are noted which depart from statistical expectation. Although this could be simply a manifestation of timing noise, the relatively well determined EGRET timing residuals appear to have a sinusoidal modulation which is consistent with a planet of mass 1.7 M_o plus/sin i orbiting Geminga at a radius of 3.3 AU. Continuation of timing studies will eventually ascertain if a planet is orbiting Geminga.