Hot Jupiter - Ultra-short-period Planets

Ultra-short-period planets are a class of hot Jupiters with orbital periods below 1 day and occur only around stars of less than about 1.25 solar masses. They orbit closer to stars than any other described planetary object.

Five ultra-short-period planets have been identified in the region of the Milky Way known as the galactic bulge. They were observed by the Hubble Space Telescope and first described by researchers from the Space Telescope Science Institute, the Universidad Catolica de Chile, Uppsala University, the High Altitude Observatory, the INAF–Osservatorio Astronomico di Padova and the University of California at Los Angeles.

More transiting hot Jupiters have been discovered, such as WASP-18b, that have orbital periods of less than one day that do not support the hypothesis of the research above.