An eccentric Jupiter is a

Jovian planet The giant planets constitute a diverse type of planet much larger than Earth. They are usually primarily composed of low-boiling-point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. Ther ...

that orbits its

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

in an

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

orbit. Note: this study treats eccentric Jupiters as giant planets having an orbital eccentricity of 0.1 or greater. Eccentric Jupiters may probably disqualify a

planetary system A planetary system is a set of gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...

from having Earth-like planets (though not always from having habitable exomoons) in it because a massive

gas giant A gas giant is a giant planet composed mainly of hydrogen and helium. Gas giants are also called failed stars because they contain the same basic elements as a star. Jupiter and Saturn are the gas giants of the Solar System. The term "gas giant" ...

with an eccentric orbit may remove all

Earth mass An Earth mass (denoted as M_\mathrm or M_\oplus, where ⊕ is the standard astronomical symbol for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative uncertainty ...

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

s from the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

, if not from the system entirely. The planets of the solar system, except for

Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...

, have orbits with an eccentricity of less than 0.1 and are moving in a state close to a perfect circle. However, two-thirds of the exoplanets discovered in 2006 have elliptical orbits with an eccentricity of 0.2 or more. The typical exoplanet with an orbital period greater than 5 days has a median eccentricity of 0.23. This, together with

Hot Jupiter Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...

, provided an opportunity to fundamentally review the theory of solar system formation so far.

History of discovery

Eccentric Jupiter was first confirmed in 1996. The first exoplanet around

main sequence star Main may refer to: Geography * Main River (disambiguation) **Most commonly the Main (river) in Germany * Main, Iran, a village in Fars Province *"Spanish Main", the Caribbean coasts of mainland Spanish territories in the 16th and 17th centuries ...

was discovered in

51 Pegasi 51 Pegasi (abbreviated 51 Peg), formally named Helvetios , is a Sun-like star located from Earth in the constellation of Pegasus. It was the first main-sequence star found to have an exoplanet (designated 51 Pegasi b, officially named ...

the previous year, but apart from that, a planet with a very large eccentricity was found around 16 Cygni, although it was farther from the central star. The celestial bodies that revolve around 16 Cygni and 70 Virginis with an eccentricity of more than 0.5 were initially regarded as brown dwarfs. However, due to the discovery of similar objects with the

mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

and the existence of multiple planetary systems, it has become widely recognized as a typical example of exoplanets.

Origin of orbit formation

There are various theories about the origin of the distorted orbit compared to the planets of the solar system, but if there is a hot Jupiter in a multi-planetary system, it can be explained by a relatively simple model called "slingshot model". The following is an example of calculation of orbital evolution by

computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be dete ...

. In any planetary system, the orbit of the planet is initially born in a state close to a perfect circle, but if there are three or more

planets , the orbit will probably be distorted after a certain period of time. One of the planets will be thrown out of the system, and the remaining two planets will also be in orbits with a very high eccentricity. This is due to the fact that the energy exchanged between the three planets during their revolution is concentrated on a specific planet. This phenomenon almost always occurs after a certain period of time (with an error of 1-2 digits), but when there are two or less giant gas planets (that is, only Jupiter and Saturn in the solar system), it is more stable that the period of time is much longer than the life of a standard star, and it is virtually stable in a circular orbit. Therefore, there is a calculation result that each planet remains in a circular orbit semi-permanently in the solar system. On the other hand, if there are three or more giant gas planets, the "fixed period" will be greatly affected by the mass and orbital spacing of the planets. If a massive planet has a narrow orbital spacing, the period will be shorter than the life of the star, and orbital crossing will occur shortly after the formation of the planetary system. Another theory has pointed out that the interaction between giant planets and

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

s may increase eccentricity. However, it is difficult to explain an eccentric planet with an eccentricity exceeding 0.4 with this mechanism. Also, if the planet is orbiting a star belonging to a

star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or '' galaxy'', although, broadly speak ...

, the

gravity In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stro ...

of the

companion star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...

may increase the orbital eccentricity.

Relation to hot Jupiter

There is a theory that Hot Jupiter, which revolves near the main star, is a change in the orbit of the eccentric planet. Eccentric Jupiter is near point 0.05 stellar in AU if it has an elongated elliptical orbit so as to approach to the extent, from the main star tidal brake is applied to the revolution around the near point by. As a result, while maintaining the near point distance far point only the distance is gradually reduced, ultimately is that settle on a smaller radius of the circular orbit . For example, the eccentric planet HD 80606 b has an extremely elliptical orbit with a perigee distance of 0.03 au and apogee distance of 0.87 au, and may be a celestial body that is transitioning to a hot Jupiter with an orbital radius of 0.03 au. The problem with this model is that tidal forces weaken rapidly over distance (inversely proportional to the cube of the distance), so you must continue to orbit closer to the main star to get sufficient braking. As an example, if another giant planet exists outside the celestial body that is transitioning to Hot Jupiter, its gravity will change the perigee distance of the inner planet, and if it is too far from the main star, the tidal force will be almost ineffective. In addition, Hot Jupiter has been found at a position slightly distant from the main star (0.1 au or more), but another model is needed to explain these.

Confusion with multiplanetary system

Some of the detected eccentric planets may actually be multiple planets with near-circular orbits. The majority of eccentric planets have been reported based on radial velocity measurements using

Doppler spectroscopy Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in t ...

by which eccentricity is directly measurable. In the case where the planet is in a circular orbit, the fluctuation pattern of the radial velocity is a simple

sine curve A sine wave, sinusoidal wave, or just sinusoid is a mathematical curve defined in terms of the ''sine'' trigonometric function, of which it is the graph. It is a type of continuous wave and also a smooth periodic function. It occurs often in ma ...

, but in the case of an elliptical orbit, it deviates from the sine curve and is recognized as an eccentric planet. However, such a distorted waveform can also occur due to the synthesis of radial velocity fluctuations caused by multiple planets. The two cannot be distinguished if the radial velocity sampling is insufficient (the number of times is small, only a part of the orbital period can be covered, etc.) . In this situation, the simplest model that can reproduce the observations is preferred to be a single eccentric planet rather than a multi-planetary system. Due to these circumstances, there are cases where the planet, which was initially reported as an eccentric planet, turns out to be a multi-planetary system with a low eccentricity due to the accumulation of observations and improvements in analytical techniques. As an example, a study that re-examined 82 planetary systems that were alleged to have a single eccentric planet in 2013 found that multi-planetary models were statistically clearly better than single-planet models. 9 have been found. The situation where multiple planetary systems and eccentric planets are confused is likely to occur in cases where the waveform distortion is relatively small, such as when the eccentricity is 0.5 or less when interpreted as a single planet. On the other hand, the eccentric planet, which has an extreme orbit with an eccentricity of 0.5 or more, is considered to have little room for being mistaken for a multiplanetary system.

List

Possible

planets near eccentric Jupiters:

References