Tyche is a hypothetical

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" ...

located in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

Oort cloud The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging from ...

, first proposed in 1999 by astrophysicists John Matese, Patrick Whitman and Daniel Whitmire of the

University of Louisiana at Lafayette The University of Louisiana at Lafayette (UL Lafayette, University of Louisiana, ULL, or UL) is a public research university in Lafayette, Louisiana. It has the largest enrollment within the nine-campus University of Louisiana System and the s ...

. They argued that evidence of Tyche's existence could be seen in a supposed bias in the points of origin for

long-period comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are ...

s. More recently, Matese and Whitmire re-evaluated the comet data and noted that Tyche, if it existed, would be detectable in the archive of data that was collected by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2 ...

(WISE) telescope. In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist.

History

Matese, Whitmire and their colleague Patrick Whitman first proposed the existence of this planet in 1999, based on observations of the orbits of long-period comets. Most astronomers agree that long-period comets (those with orbits of thousands to millions of years) have a roughly isotropic distribution; that is, they arrive at random from every point in the sky. Because comets are volatile and dissipate over time, astronomers suspect that they must be held in a spherical cloud tens of thousands of AU distant (known as the

) for most of their existence. However, Matese and Whitmire claimed that rather than arriving from random points across the sky as is commonly thought, comet orbits were in fact clustered in a band inclined to the orbital plane of the planets. Such clustering could be explained if they were disturbed by an unseen object at least as large as

Jupiter Jupiter is the fifth planet from the Sun and the 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 slightly less than one-thousand ...

, possibly a

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

, located in the outer part of the

. They also suggested that such an object might explain the

trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au). Typically ...

Sedna's peculiar orbit. However, the sample size of Oort comets was small and the results were inconclusive.

Orbit

Whitmire and Matese speculated that Tyche's orbit would lie at approximately 500 times

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...

's distance, some from the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, a little less than one quarter of a

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

. This is well within the

, whose boundary is estimated to be beyond 50,000 AU. It would have an orbital period of roughly 1.8 million years. A failed search of older

IRAS The Infrared Astronomical Satellite ( Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten ...

data suggests that an object of would need to have a distance greater than 10,000 AU. Such a planet would orbit in a plane different from the ecliptic, and would probably have been in a wide-binary orbit at the time of its formation. Wide binaries may form through capture during the dissolution of a star's birth cluster.

Mass

In 2011, Whitmire and Matese speculated that the hypothesized planet could be up to four times the mass of

and have a relatively high temperature of approximately , due to residual heat from its formation and Kelvin–Helmholtz heating. It would be insufficiently massive to undergo

nuclear fusion Nuclear fusion is a reaction in which two or more atomic nuclei are combined to form one or more different atomic nuclei and subatomic particles ( neutrons or protons). The difference in mass between the reactants and products is manife ...

reactions in its interior, a process that occurs in objects above roughly 13

Jupiter mass Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is by ...

es. Although more massive than Jupiter, Tyche would be about Jupiter's size since degenerate pressure causes massive gas giants to increase only in density, not in size, relative to their mass. If Tyche was to be found, it was expected to be found by the end of 2013 and only be 1–2 Jupiter masses.

Origin of name

Tyche Tyche (; Ancient Greek: Τύχη ''Túkhē'', 'Luck', , ; Roman equivalent: Fortuna) was the presiding tutelary deity who governed the fortune and prosperity of a city, its destiny. In Classical Greek mythology, she is the daughter of Aphrod ...

(, meaning "fortune" or "luck" in

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

) was the

goddess of fortune and prosperity. The name was chosen to avoid confusion with an earlier similar hypothesis that the Sun has a dim companion named ''

Nemesis In ancient Greek religion, Nemesis, also called Rhamnousia or Rhamnusia ( grc, Ῥαμνουσία, Rhamnousía, the goddess of Rhamnous), was the goddess who personifies retribution, a central concept in the Greek world view. Etymology The ...

'', whose gravity triggers influxes of comets into the inner Solar System, leading to mass-extinctions on

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

was the name of the "good sister" of

. This name was first used for an outer Oort cloud object by

J. Davy Kirkpatrick J. Davy Kirkpatrick is an American astronomer at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, California. Kirkpatrick's research was named one of the top ten science accomplishments of the fi ...

at the Infrared Processing and Analysis Center of the California Institute of Technology.

WISE mission

The

(WISE)

space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the American Orbiting Astronomical Observatory, OAO-2 launch ...

has completed an all-sky infrared survey that includes areas where Whitmire and Matese anticipate that Tyche may be found. On March 14, 2012, the first-pass all-sky survey catalog of the WISE mission was released. The co-added (AllWISE) post-cryo second survey of the sky was released at the end of 2013.Wide-field Infrared Survey Explorer
/ref> On March 7, 2014, NASA reported that the WISE telescope had ruled out the possibility of a Saturn-sized object at 10,000 AU, and a Jupiter-sized or larger object out to 26,000 AU (0.4

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s).

Notes

References

{{Portal bar, Stars, Spaceflight, Outer space, Science Hypothetical bodies of the Solar System Solar System dynamic theories Hypothetical planets Hypothetical trans-Neptunian objects Oort cloud Astronomical controversies