Hot Jupiter
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Artist's impression of "roaster" extrasolar planet HD 209458b (Osiris). |
Hot Jupiter (also called
roaster,
pegasid or
Pegasi planet) is a class of
extrasolar planets whose mass is close to or exceeds that of
Jupiter (1.9 × 10
27 kg), but unlike in our own
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. In comparison, a Hot Jupiter is about
eight times closer to its star than
Mercury is to the Sun.
Hot Jupiters have some common characteristics:#They have a much greater chance of
transiting their star as seen from Earth than planets of the same mass in larger orbits.#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.#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.#They all have low
eccentricities. This is because their orbits have been circularised, or are being circularised, by the process of
libration. This also causes the planet to synchronise its rotation and orbital periods, so it always presents the same face to its parent 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.
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Hot Jupiters (along left edge, including red dots) discovered up to and including 31 August 2004. |
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Inside Exoplanets: Motley Crew of Worlds Share Common Thread
