On of four known planets of Mu Arae, a relatively Sun-like G-type yellow star some fifty-one light years from the Solar System. The star has been given the name Cervantes after the Spanish writer, and each of its four planets carries the name of a character from his book Don Quixote. Dulcinea was the object of the courtly affection of Don Quixote himself (who also gave his name to one of these planets, Quijote, the third planet from the star).
Dulcinea orbits much more closely around Cervantes than Quijote. Indeed, it is the nearest of the four worlds to its star, with an average distance of just 0.1 AU (about a quarter of the distance of Mercury from the Sun). This means that Dulcinea is an intensely hot world, with an estimated temperature of some 900 K (or about 600°C). It also means that Dulcinea's orbit is a rapid one, so that a 'year' on the planet lasts less than ten days).
Dulcinea is a massive planet, with more than ten times the mass of Earth. Nonetheless, it was at one time considered that it might be a rocky terrestrial planet like Earth or Mars, though this is now thought unlikely. Instead, it seems to have a massive core surrounded by thick layers of atmosphere, somewhat like Neptune in the Solar System, though, due to its proximity to the star, a great deal hotter. Because of this similarity of structure, planets like Dulcinea are sometimes classified as 'hot Neptunes'.