Hot Neptune

A hot Neptune is a type of giant planet with a mass similar to that of Uranus or Neptune in an orbit close to its star, normally less than 1 AU. The first hot Neptune to be discovered with certainty was Gliese 436 b in 2007, an exoplanet about 33 light years away. Recent observations have revealed a larger potential population of hot Neptunes in the Milky Way than previously thought.

General characteristics

Because of their close proximity to their parent star, hot Neptunes have a much greater rate and chance of transiting their star as seen from a farther outlying point, than planets of the same mass in larger orbits. This increases the chances of discovering them by transit-based observation methods.

The most notable transiting hot Neptunes are Gliese 436 b and HAT-P-11b, which was recently observed by the Kepler mission. Gliese 436 b (also known as GJ 436b) was the first hot Neptune to be discovered with certainty in 2007. The exoplanet Mu Arae c (or HD 160691 c) discovered in 2004 might also be a hot Neptune, but it has not been determined definitively.