The planet 55 Cancri e orbits its sun in just over 17 hours.
http://www.newscientist.com/article/...ef=online-news
More here ...
http://en.wikipedia.org/wiki/55_Cancri_e
By my calculations, assuming its sun has the same mass as ours, its orbital radius would be about 2.4 million kms. In comparison Mercury, orbits our Sun at about 58 million kms.
I'm surprised that a planet could form this close to its sun.
Rob.