Given that some exoplanets, particular "Hot Jupiters", orbit very closely to their parent star, how hot can these planets become?
What is the hottest exoplanet discovered so far?
The temperature of an exoplanet is dependent on a number of factors, including:
Recent discoveries, such as reported in the article "Sizzling Planet Makes Some Stars Look Cool" (Than, 2007), have found that some exoplanets are hotter than some types of stars.
For example, the exoplanet HD 149026b has a star-facing side of over 2000C (3700F), this planet reflects so little light that it would appear like a "glowing piece of charcoal". It is believed (from the article) that the planet is tidally locked and the 'dark side' of the planet is believed to be substantially cooler.