hot Jupiter

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An artist's impression of a hot Jupiter planet.

Hot Jupiters (also called oven roasters, epistellar jovians, pegasids or pegasean planets)^{[citation needed]} are a class of extrasolar planet whose mass is close to or exceeds that of Jupiter (1.9 × 10²⁷ kg), but unlike in the Solar System, where Jupiter orbits at 5.2 AU, the planets referred to as hot Jupiters orbit within approximately 0.1 AU^{[citation needed]} of their parent stars.

One of the most well-known hot Jupiters is 51 Pegasi b, nicknamed Bellerophon, discovered in 1995 and was the first extrasolar planet found orbiting a Sun-like star.

General characteristics

Hot Jupiters (along left edge, including most of planets detected using the transit method, indicated with black dots) discovered up to 2009-12-07.

Hot Jupiters have some common characteristics:

1. They have a much greater chance of transiting their star as seen from a farther outlying point than planets of the same mass in larger orbits. The most famous of these are HD 209458 b, the first transiting hot Jupiter found, and HAT-P-7b, which was recently observed by the Kepler mission.
2. 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 against its background star during a transit, the planet's ingress and egress boundaries are harder to determine.
3. They are all thought to have migrated to their present positions because there would not have been enough material so close to the star for a planet of that mass to have formed in situ.
4. They all have 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.

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 other known types of planets.

Hot Jupiters are thought to form at a distance from the star beyond the ice line, where the planet can form from rock, ice and gasses. The planets then migrate inwards to the sun where they eventually form a stable orbit^[1]. The planets usually move by type 2 migrations, or possibly via interaction with other planets. The migration happens during the solar nebula phase, and will typically stop when the sun enters its T-Tauri phase. The strong stellar winds at this time remove most of the remaining nebula.

After hot Jupiters get their atmospheres and outer layers stripped away, their cores may become chthonian planets. Losing of the outermost layers depends on the size and the material of the planet and the distance from the star. In a typical system a gas giant orbiting 0.02 AU around its parent star loses 5-7% of its mass during its lifetime, but orbiting closer than 0.015 AU can mean evaporation of the whole planet except for its core.^[2]

Terrestrial planets in systems with hot Jupiters

Simulations have shown that the migration of a Jupiter-sized planet through the inner protoplanetary disk (the region between 5 and 0.1 AU from the star) is not as destructive as one might assume. More than 60% of the solid disk materials in that region are scattered outward, including planetesimals and protoplanets, allowing the planet-forming disk to reform in the gas giant's wake.^[3] In the simulation, planets up to 2 Earth masses were able to form in the habitable zone after the hot Jupiter passed through and its orbit stabilized at 0.1 AU. Due to the mixing of inner solar system material with outer solar system material from beyond the "snow line", simulations indicated that the terrestrial planets that formed after a hot Jupiter's passage would be particularly water-rich.^[3]

See also

• Cold Jupiter
• Hot Neptune

References

External links

• Inside Exoplanets: Motley Crew of Worlds Share Common Thread
• NASA: Global temperature map of an exoplanet
• First known theoretical prediction about existence of Hot Jupiters - by Otto Struve in 1952.

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