Tyche (hypothetical planet)
Encyclopedia
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
planet located in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
's Oort cloud
Oort cloud
The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
, first proposed in 1999 by astronomer John Matese of the University of Louisiana at Lafayette
University of Louisiana at Lafayette
The University of Louisiana at Lafayette, or UL Lafayette, is a coeducational, public research university located in Lafayette, Louisiana, in the heart of Acadiana...
. Matese and his colleague Daniel Whitmire argue that evidence of Tyche's existence can be seen in a supposed bias in the points of origin for long-period comets. They noted that Tyche, if it exists, should be detectable in the archive of data that was collected by NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009, and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off...
(WISE) telescope. However, several astronomers have voiced skepticism of this object's existence. Analysis over the next couple of years will be needed to determine if WISE has actually detected such a world or not.
History
Matese first proposed the existence of this planet in 1999, based on his observations of the orbits of long-period comets. Most astronomers agree that long period comets (those with orbits of thousands of years) have an isotropic distribution; that is, they arrive at random for every point in the sky. Because comets are volatileVolatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
and dissipate over time, astronomers suspect that they must be held in a spherical cloud tens of thousands of AU distant (known as the Oort cloud
Oort cloud
The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
) for most of their existence. However, Matese 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
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
. Such clustering could be explained if they were disturbed by an unseen object at least as large as Jupiter, possibly a brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
, located in the outer part of the Oort cloud. He also suggested that such an object might also explain the trans-Neptunian object
Trans-Neptunian object
A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...
Sedna
90377 Sedna
90377 Sedna is a trans-Neptunian object discovered in 2003, which was about three times as far from the Sun as Neptune. For most of its orbit it is even further from the Sun, with its aphelion estimated at 960 astronomical units , making it one of the most distant known objects in the Solar System...
's peculiar orbit. However, his sample size was small and the results were inconclusive.
Orbit
Whitmire and Matese speculate that Tyche's orbit would lie at approximately 500 times Neptune's distance; equivalent to 15,000 AU from the SunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
, a little less than one quarter of a light year. This is still well within the Oort cloud
Oort cloud
The Oort cloud , or the Öpik–Oort cloud , is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun...
, 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
IRAS
The Infrared Astronomical Satellite was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths....
data suggests that an object of 5 MJ
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
would need to have a distance greater than 10,000 AU. Such a planet would orbit in a different plane in orientation to our current planet orbits, and probably formed in a wide-binary orbit. Wide binaries may form through capture during the dissolution of a star's birth cluster
Open cluster
An open cluster is a group of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way Galaxy, and many more are thought to exist...
.
Mass
Whitmire and Matese speculate that the hypothesized planet could be up to four times the mass of JupiterJupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
and have a relatively high temperature of approximately 200 K (−73°C), due to residual heat from its formation and Kelvin–Helmholtz heating. It would be insufficiently massive to undergo nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
reactions in its interior, a process which occurs in objects above roughly 13 Jupiter mass
Jupiter mass
Jupiter mass , is the unit of mass equal to the total mass of the planet Jupiter . Jupiter mass is used to describe masses of the gas giants, such as the outer planets and extrasolar planets. It is also used in describing brown dwarfs....
es. Although more massive than Jupiter, Tyche would be about Jupiter's size since degenerate pressure causes massive gas giants to only increase in density, not in size, relative to their mass.
Origin of name
TycheTyche
In ancient Greek city cults, Tyche was the presiding tutelary deity that governed the fortune and prosperity of a city, its destiny....
(Τύχη, meaning "fortune" or "luck" in Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
) was the Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
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
Nemesis (star)
Nemesis is a hypothetical hard-to-detect red dwarf star, white dwarf star or brown dwarf, originally postulated in 1984 to be orbiting the Sun at a distance of about 95,000 AU , somewhat beyond the Oort cloud, to explain a perceived cycle of mass extinctions in the geological record, which seem to...
, whose gravity triggers influxes of comets into the inner Solar System, leading to mass-extinctions
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Tyche
Tyche
In ancient Greek city cults, Tyche was the presiding tutelary deity that governed the fortune and prosperity of a city, its destiny....
was the name of the "good sister" of Nemesis
Nemesis (mythology)
In Greek mythology, Nemesis , also called Rhamnousia/Rhamnusia at her sanctuary at Rhamnous, north of Marathon, was the spirit of divine retribution against those who succumb to hubris . The Greeks personified vengeful fate as a remorseless goddess: the goddess of revenge...
. This name was first used for an outer Oort cloud object by Davy Kirpatrick at the Infrared Processing and Analysis Center of the California Institute of Technology.
Ongoing research
The Wide-field Infrared Survey ExplorerWide-field Infrared Survey Explorer
Wide-field Infrared Survey Explorer is a NASA infrared-wavelength astronomical space telescope launched on December 14, 2009, and decommissioned/hibernated on February 17, 2011 when its transmitter was turned off...
(WISE) space telescope has completed an all-sky infrared survey that includes areas where Whitmire and Matise anticipate that Tyche may be found. However the vast amount of survey data will not be fully analyzed until March 2012 at the earliest.
See also
- Planets beyond NeptunePlanets beyond NeptuneFollowing the discovery of the planet Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The search began in the mid-19th century but culminated at the start of the 20th with Percival Lowell's quest for Planet X...
- Kelvin–Helmholtz heating
- Nemesis (hypothetical star)
- Vulcan (hypothetical planet)Vulcan (hypothetical planet)Vulcan was a small planet proposed to exist in an orbit between Mercury and the Sun. In an attempt to explain peculiarities of Mercury's orbit, in the 19th-century French mathematician Urbain Jean Joseph Le Verrier hypothesized that they were the result of another planet, which he named Vulcan...