Astrometric or radial velocity measurements have not yet detected companions around Tau Ceti, but given current search refinement, this only excludes substellar companions such as large brown dwarfs. Because of its debris disk, any planet orbiting Tau Ceti would face far more impact events than the Earth. Despite this hurdle to habitability, its solar analog (Sun-like) characteristics have led to widespread interest in the star. Given its stability and similarity to the Sun, Tau Ceti is consistently listed as a target for the Search for Extra-Terrestrial Intelligence (SETI), and it appears in some science fiction literature.
Unlike other prominent stars, Tau Ceti does not have a widely recognized traditional name. It can be seen with the unaided eye as a faint third-magnitude star. As seen from Tau Ceti, the Sun would be a third-magnitude star in the constellation Boötes.
The Tau Ceti system is believed to have only one stellar component. A dim optical companion has been observed, which is possibly gravitationally bound, but it is more than 10 arcseconds distant from the primary. No astrometric or radial velocity perturbations have been deduced, suggesting a star that does not have a large companion in a close orbit, such as a "hot Jupiter". Any potential gas giants around Tau Ceti are likely to be located more at Jupiter-like distances.
Most of what is known about the physical properties of Tau Ceti has been determined through spectroscopic measurements. By comparing the spectrum to computed models of stellar evolution, the age, mass, radius and luminosity of Tau Ceti can be estimated. However, using an astronomical interferometer, measurements of the radius of the star can be made directly to an accuracy of 0.5%. It deploys a long baseline to measure angles much smaller than can be resolved with a conventional telescope. Through this means, the radius of Tau Ceti has been measured as 79.3 ± 0.4% of the solar radius.2 This is about the size that is expected for a star with somewhat lower mass than the Sun.
Principal factors driving research interest in Tau Ceti are its Sun-like characteristics and their implications for possible planets and life. Hall and Lockwood report that "the terms 'solarlike star,' 'solar analog,' and 'solar twin' are progressively restrictive descriptions." Tau Ceti fits the second category, given its similar mass and low variability, but relative lack of metals.nb 7 The similarities have inspired popular culture references for decades, as well as scientific examination.
Tau Ceti was a target of a few radial velocity planetary searches, which have failed to find any periodical variations attributable to planets. The velocity precision reached so far is about 11 m/s measured over a five year time span. This result excludes the presence of hot Jupiters, and probably excludes any planets with minimum mass greater than or equal to Jupiter's mass and with orbital periods less than 15 years. In addition, a survey of nearby stars by the Hubble Space Telescope's Wide Field and Planetary Camera was completed in 1999, including a search for faint companions to Tau Ceti; none were discovered to limits of the telescope's resolving power.
These searches only excluded larger brown dwarf bodies and giant planets so a smaller, Earth-like planet in orbit around the star is not precluded. If "hot Jupiters" did exist in close orbit they would likely disrupt the star's habitable zone; their exclusion is thus a positive for the possibility of Earth-like planets. General research has shown a positive correlation between the presence of extrasolar planets and a relatively high metal parent star, suggesting that stars with lower metallicity such as Tau Ceti have a reduced chance of possessing planets. The evidence of a thick debris disk increases the likelihood that one or more rocky planets orbit the star, however, even if it suggests a high bombardment scenario. If planets are found, subsequent searches, with telescopes of sufficient resolution, would look for atmospheric water and temperatures suitable for habitability. Primitive life might reveal itself through an atmospheric composition unlikely to be inorganic, just as oxygen on Earth is indicative of life.
Tau Ceti in space opera:
- In Isaac Asimov's Robot and Foundation novels?, the planet Aurora? and its two asteroidal satellites orbit Tau Ceti.
- In Lois McMaster Bujold's? Vorkosigan Saga? series, Tau Ceti has a major human-inhabited planet and is an important wormhole crossroad. The Tau Cetans are a planetary polity.
- In Larry Niven's Known Space series, the human colony of Plateau orbited Tau Ceti.
- In Dan Simmons's? Hyperion Cantos?, Tau Ceti is orbited by Tau Ceti Center?, capital of the Hegemony of Man?.
- In Ursula K. Le Guin's? The Dispossessed?, the action takes place in a fictional double planet system orbiting Tau Ceti. The two planets are called Anarres? and Urras?.
- In C.J. Cherryh's Hugo Award-Winning novel Downbelow Station, the space station referenced in the book's title (Pell Station) orbits a planet, Downbelow, in the Tau Ceti system inhabited by the alien Hisa race.
- In Julian May's? Galactic Milieu? trilogy, Tau Ceti is orbited by the planet Molakar?, inhabited by the alien race Krondaku and destroyed in the Metapsychic Rebellion.
- In Jeri Taylor's? Star Trek: Voyager? novel, Kathryn Janeway lost her father and her fiancé in a crash on Tau Ceti Prime?.
- System with? planets in Providence Station setting.
- In the game Escape Velocity it us the system of planet Tau Ceti IV and it's moon Merlin.