Hot Jupiter

Hot Jupiter ( German: Hot Jupiter) refers to a class of exoplanets with masses around that of Jupiter ( 1.9 × 1027 kg ) equals or exceeds, and is strongly heated by its proximity to the central star.

In contrast to the conditions in our solar system, these gas planets orbit their central star is not at an average distance of 5 astronomical units, but only about 0.05 AU. This is their distance to the star is only about 1 /8 ( 12.5%) of the distance between Mercury and the Sun, thereby having a correspondingly high surface temperature (several hundred degrees Kelvin ).

Examples are 51 Pegasi b ( Bellerophon ), HD 209458 b ( Osiris ) and the exoplanets in the systems HD 195 019 and HD 189733rd

Properties

Hot Jupiters have some similarities:

• The probability to observe passage of the earth is considerably higher than at the higher planetary orbits.
• Due to the strong insolation ( sunlight), they have a lower density than would normally be the case. This has implications for the determination of the diameter, since due to the limb darkening during the transit the inlet and outlet boundaries are difficult to determine.
• When all the planets of this type, it is assumed that they only later in their current orbit reached (migration), because sufficient material could not be present in such a small distance to the central star to form a planet of this mass in situ.
• Their orbits have low eccentricity. This is due to the libration. She is also responsible for ensuring that the planet synchronize their rotation with the orbit of the central star and therefore always with the same side on this show ( synchronous rotation ).
• They occur in the solar neighborhood F, G and K dwarfs only with a probability of 1.2 %, which is quite rare. In contrast, about 25 % of the metal-rich stars in the solar neighborhood are likely to have exoplanets.
• Hot Jupiter be with a very low probability to subgiant found. These stars are the first phase of development after F, G and K dwarfs have left the main sequence and turn into red giants due to shell burning. Probably the Hot Jupiter be destroyed by tidal forces.
• The orbital period of Jupiter is hot between one to five days, with their mass rarely exceeds 2 Jupiter masses
• The path axis of the hot Jupiter is often not in the plane of rotation of the star. This can be observed by means of star spots which move slowly across the surface of the star. If there is a covering of the patch by a planetary star, this results in a deep minimum. Had the rotation axis of the star and the orbital plane of the planets aligned, then these coverages would repeat. This is usually the case with other exoplanets, while this is rare in Hot Jupiters. Therefore, the path of hot Jupiters may have been influenced by scattering with other planets because it is assumed that all planetary orbits lie in the origin in the plane of rotation of its parent star.
• Some hot Jupiter orbit their star at a distance of only one stellar radius. These exoplanets are surrounded by vast clouds of gas that extend beyond the Roche limit volume. The gas planets are eroded by ablative stellar winds and intense radiation heats its atmosphere to the extent that the Brownian motion exceeds the gravitational potential of the planet.
• For hot Jupiters with orbital radius of less than 0.08 AE, the diameter of the gas giants are much greater than would be expected only by the incidence of electromagnetic radiation. Either save the planet for reasons unknown heat very well or there is an additional source of energy unknown up to 1027 erg / s
• Hot Jupiter in her tight orbits around their star to increase its rotational speed due to tidal effects. The higher rotational speed, in turn, increases the magnetic activity of the star in the form of star spots and flares. This makes the observation of the Hot Jupiter and the age determination of Plant systems, since the rotation speed of single stars is a good age indicator.

Hot Jupiter exoplanets are those that are the easiest to detect by measuring the radial velocity. Because as a result of its close orbit, they induce a very strong and fast in comparison to other planets oscillation of the central star.

Development

Theoretical calculations suggest that gas giants occur near the ice line, which is the most stars at a distance of a few astronomical units. This is also supported by observations that no hot Jupiter are found in young stars shortly after the dissolution of the protoplanetary disk. With many hot Jupiters: the axis is inclined to the rotation axis of the central star, which is why assumed that the planets were scattered out of their original path. This can be done through interaction with the protoplanetary disk or another planet. The resulting highly elliptical orbit is then circularized by tidal forces. Probably many orbits of hot Jupiters are not stable long-term, due to the Darwin instability or the Kozai effect the gas planets could merge with the central star. Merging would be as a Luminous Red Nova observed and the estimated rate of a merger burst from a hot Jupiter is an event every 10 years in the Milky Way.

Alternative approaches assume that the gas planet due to friction in the circumstellar disk lose torque and migrate inward. This movement comes in a close orbit around the central star to a halt because the inner region of the disk is already excluded in young stellar objects of material or because tidal waves between the star and the planet prevent further movement.

The physical properties of hot Jupiter are quite different. In particular, some have large radii and low mean densities, while other hot Jupiters have a dense core. This diversity could be the result of collisions of the gas planets with Earth-like rocky planets. With the migration of the giant planets in his tight track other planets could be collected and released during the collision energy would lead to a sharp increase in the radius of the gas planets. Sinking the remains of the rocky planets in the core of the giant planets, the stronger the gravitational force leads after cooling the planet's atmosphere to a contraction.