Constraining the Rotation Rate of Transiting Extrasolar Planets by Oblateness Measurements

Abstract

The solar system gas giant planets are oblate due to their rapid rotation. A measurement of the planet's projected oblateness would constrain the planet's rotational period. Planets that are synchronously rotating with their orbital revolution will be rotating too slowly to be significantly oblate; these include planets with orbital semimajor axes <1 AU, about 20 of which will be at >0.2 AU. Furthermore, part-per-million photometric precision (reached after averaging over several orbital periods) is expected from three other space telescopes to be launched within the next three years. Thus, an oblateness measurement of a transiting giant planet is realistic in the near future.