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Hot jupiter

An artists impression of a Hot Jupiter

Hot Jupiters (also sometimes called roaster planets) are a class of extrasolar planets which have similar characteristics to the planet Jupiter but have much warmer surface temperatures due to orbiting close to the host star. 

An example of a Hot Jupiter is 51 Pegasi b (also known as Bellerophon), a planet discovered in 1995. It was the first extrasolar planet discovered orbiting a sun like star.

Characteristics of Hot JupitersEdit

  • They have similar characteristics to Jupiter. Jupiter experiences cold temperatures due to its distance from the Sun. Hot Jupiters however, orbit much more closely to its host star and as such experience high surface temperatures.
  • Due to high levels of insolation they are of a lower density than they would otherwise be. This has implications for radius determination, because due to limb darkening of the planet's background star during a transit, the planet's ingress and egress boundaries are harder to determine.
  • Most of these have nearly circular orbits (low eccentricities). This is because their orbits have been circularized, or are being circularized, by the process of libration. This also causes the planet to synchronize its rotation and orbital periods, so it always presents the same face to its parent star — the planet becomes tidally locked to the star.
  • They exhibit high-speed winds distributing the heat from the day side to the night side, thus the temperature difference between the two sides is relatively low.

Ultra-short-period planetsEdit

Ultra-short-period planets are usually Hot Jupiters which have orbital periods of less than one day, occurring only around stars of less than about 1.25 solar masses. They orbit closer to stars than any other described planetary object.

Puffy planetsEdit

Puffy planets are sometimes called Hot Saturns, due to their similarity in density with the planet Saturn. Puffy planets may orbit close to their stars since the intense heat from the star and internal heating within the planet will help inflate the planet's atmosphere.


Theoretical research suggests that Hot Jupiters are not likely to have Moons, due to both a small Hill sphere and the tidal forces or the stars they orbit, which would destabilize the satellites' orbits, the latter process being stronger for larger moons. This means that for most hot Jupiters stable satellites would be small, asteroid-sized bodies.

Hot Jupiters around Red GiantsEdit

It has been proposed that, even though no planet of this type has been found, gas giants orbiting red giant stars similar to that of Jupiter could be hot Jupiters too due to the intense irradiation they would receive from their stars.

It has been proposed, and rather likely that, in the Solar System, Jupiter will become a Hot Jupiter when the Sun becomes a red giant.

See alsoEdit

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