Hot Jupiter
Hot Jupiters (also called roaster planets,epistellar jovians,pegasids or pegasean planets) are a class of exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital radii with semi-major axes from 0.015 to 0.5 astronomical units (2.2×106 to 74.8×106 km). The close proximity to their stars and high surface temperatures resulted in the moniker "hot Jupiters".
Hot Jupiters are the easiest extrasolar planets to detect via the radial-velocity method, because the oscillations they induce in their parent stars' motion are relatively large and rapid compared to those of other known types of planets. One of the best-known hot Jupiters is 51 Pegasi b. Discovered in 1995, it was the first extrasolar planet found orbiting a Sun-like star. 51 Pegasi b has an orbital period of about 4 days.
Though there is diversity among hot Jupiters, they do share some common properties.
There are two general schools of thought regarding the origin of hot Jupiters: formation at a distance followed by inward migration and in-situ formation at the distances at which they're currently observed. The prevalent view is migration.
In the migration hypothesis, hot Jupiters are thought to form at a distance from the star beyond the frost line, where the planet can form from rock, ice and gases. The planets then migrate inwards to the star where they eventually form a stable orbit. The planets usually move by type II orbital migration, or possibly via interaction with other planets or a stellar companion. It has been shown that approximately 50% of hot Jupiters have distant Jupiter-mass or larger companions. The migration happens during the solar nebula phase, i.e. when gas is still present. Energetic stellar photons and strong stellar winds at this time remove most of the remaining nebula.
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