What class of exoplanet is a Jupiter-like gas giant orbiting very close to its star? The answer is a hot Jupiter.
Hot Jupiters are gas-giant exoplanets with large masses and very short orbital periods. Their close orbits expose them to intense stellar radiation, producing extremely hot atmospheres and often causing their outer layers to expand. Many are tidally locked, meaning the same hemisphere continually faces the star.
The name describes both their composition and environment: they are broadly comparable to Jupiter in mass and gaseous makeup, but they orbit far closer to their stars than Jupiter does to the Sun. Their periods can be only a few days. Such planets are especially easy to find with radial-velocity surveys because their large masses and tight orbits produce a strong stellar wobble.
The first planet confirmed around a Sun-like star, 51 Pegasi b, was announced in 1995 and is a hot Jupiter. They are not the same as ice giants such as Neptune, mini-Neptunes, or super-Earths, which describe different size or composition classes. Some hot Jupiters also transit, making their atmospheres accessible to spectroscopic study.