We have made a comprehensive transit search for exoplanets down to about 2 Earth radii in the HD 209458 system , based on nearly uninterrupted broadband optical photometry obtained with the MOST ( Microvariability and Oscillations of Stars ) satellite , spanning 14 days in 2004 and 44 days in 2005 .
We have searched these data for limb-darkened transits at periods other than that of the known giant planet , from about 0.5 days to 2 weeks .
Monte Carlo statistical tests of the data with synthetic transits inserted allow us to rule out additional close-in exoplanets with sizes ranging from about 0.20 - 0.36 R _ { J } ( Jupiter radii ) , or 2.2 - 4.0 R _ { \earth } ( Earth radii ) on orbits whose planes are near that of HD 209458b .
These null results constrain theories that invoke lower-mass planets in orbits similar to HD 209458b to explain its anomalously large radius , and those that predict “ hot Earths ” due to the inward migration of HD 209458b .