Life and Planet Searches
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' progressively restrictive descriptions." Tau Ceti fits the second category, given its similar mass and low variability, but relative lack of metals. 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.
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