Hot Jupiter

Hot Jupiters (also called roasters, epistellar jovians, pegasids or pegasean planets) are a class of extrasolar planets 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 AU, the planets referred to as hot Jupiters orbit within approximately 0.05 AU of their parent stars, about one eighth the distance that Mercury orbits the Sun.

Hot Jupiters have some common characteristics:

  1. They have a much greater chance of transiting their star as seen from a further outlying point than planets of the same mass in larger orbits.
  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.

After hot Jupiters get their atmospheres stripped away, their cores may become chthonian planets.

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. 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.


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