Tau Ceti

Tau Ceti
Observational Data
Designation	Tau Ceti HD 10700
Right ascension	01h 44m 04.0829s
Declination	−15o 56′ 14.928″
Constellation	[[Cetus]]
Type of object	[[Star]]
Magnitude	Apparent Mag: 3.50 Absolute Mag: 5.69
Astrometry
Distance from Earth	11.9 ly
Radial velocity	−16.4 km/s
Proper motion	RA: −1721.94 mas/yr Dec.: 854.17 mas/yr
Parallax	273.96 ± 0.17 mas

Tau Ceti is a star similar in spectral type and mass to our sun located 11.9 light years away in the south central part of Constellation Cetus. The similarities to our own star have lead to widespread interest in the star in both astronomy and Science Fiction over the decades. Interest in Tau Ceti has recently increased due to the large, dense debris disk discovered around the star in 2004.

The Star

Tau Ceti has an apparent magnitude of 3.50, allowing it to be easily seen in the night sky, in fact from a hypothetical planet around Tau Ceti, our sun being a similar G class star, would appear as a star of similar magnitude in the night sky. Tau Ceti is the second closest class G star to us, with only Alpha Centauri A being closer, leading to much speculation and fiction about extraterrestrial life in the system.

Most of what we learned about the physical properties of Tau Ceti has been determined through spectroscopic measurements. The star is a yellow-orange, main sequence star of spectral type G8 V, though Tau Ceti is both smaller and less massive then our sun, with around 81 to 82 percent of the mass, and around 77 percent of the diameter of Sol (our sun). The star is also significantly dimmer with only 59 percent of the luminosity of our star.

Tau Ceti has a much lower metallicity in comparison to stars of similar age to our sun. Recent measurements show that Tau Ceti has only one-third of our sun’s abundance of iron. Past measurements have produced a metallicity of 22 to 74 percent of Sol’s. In all cases the metallicity is significantly lower, and using this data astronomers have estimated Tau Ceti to be around 10 billion years old.

Further evidence suggesting the star is significantly older is the slow rotation of 31 days, suggesting the star has nearly used up its hydrogen fuel for thermonuclear fusion in the core. The star's surface also appears inactive, showing a much weaker sunspot cycle then our own Sun. It is suspected that Tau Ceti is an "old dwarf" star that has migrated from the Milky Way's older "thick disk" based on its rather high velocity of 37 km/s and backtracked path through the galaxy.

Dust Disk

On July 6, 2004 a team of British astronomers using the Submillimetre Common-User Bolometer Array (SCUBA) of the James Clerk Maxwell Telescope in Hawaii announced they had found a debris disk ten times the mass of the debris (such as comets and asteroids) found in our own Solar System. The debris disk extends as far out as 55 AUs from the star and is believed created by collisions between comets and asteroids over time into smaller and smaller, more numerous pieces. The total mass of the debris field is estimated to be 1.2 times the mass of the Earth based on modelling of the dust disk observations. In comparison the debris of asteroids and comets in the Kuiper Belt only add up to 10% of the mass of Earth.

Search for Substellar Companions

Thus far no large substellar companions such as a gas giant or a brown dwarf have been found around Tau Ceti, however the search was for such worlds that orbit very close to the star.

The habitable zone where any Earth-like terrestrial worlds where liquid water could exist is centered around 0.68 AUs, or approximately the distance of Venus from the Sun. There is debate if such worlds could support complex life given the likelihood of heavy, frequent bombardment from Tau Ceti’s dense debris disk. Others astronomers argue that a giant planet in the outer system could deflect comets and asteroids away from any world that may support life, much like Jupiter does for Earth.

Astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin to search for substellar companions, including smaller, terrestrial worlds.