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79 Ceti is located around 117 light-years from Sol, in the northeastern corner (2:35:19.9-3:33:38.2, ICRS 2000.0) of Constellation Cetus, the Whale or Sea Monster -- east of Mira (Omicron Ceti), south of Delta Ceti, and northwest of Azha (Eta Eridani). It is so far away that Humans cannot see the star from Earth without binoculars or a telescope. (Note - While 79 Ceti is not included in the Bright Star Map available on-line, it is available as "BD-04 426" on the "150ly-h.zip" map file for the PC version of ChView that contains stars known to be located within 150 ly of Sol.)
© James B. Kaler, UIUC -- more information
Photo from Stars, Planet Project, and
79 Ceti (used with permission).
On March 29, 2000, astronomers announced the discovery of a Saturn-sized planet around this Sun-like star (NASA announcement and exoplanets.org -- details below). (See an animation of the planetary and potentially habitable zone orbits of the 79 Ceti system, with a table of basic orbital and physical characteristics.)
79 Ceti is a yellow-orange dwarf star of spectral and luminosity type G5 IV, with about the same mass (1.00) as Sol, about the same diameter -- 1.01 Solar (Johnson and Wright, 1983, page 651), and twice (2.0) its luminosity (exoplanets.org). As the star is unusually bright for its spectral type despite a cooler surface temperature, it is classified as a subgiant star that has begun to evolve off the main sequence as it may soon be unable to sustain hydrogen burning at its core. The star may be 1.66 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (Klaus Fuhrmann, 1998). Given its slow rotation and weak chromospheric activity, 79 Ceti appears to be a relatively old star. Useful catalogue numbers and designations for this star include: 79 Cet, GJ 9085, Hip 12048, HD 16141, BD-04 426, SAO 129992, FK5 4237, Wo 9085, and LTT 1267.
On March 29, 2000, a team of astronomers (Geoffrey W. Marcy, R. Paul Butler, and Steven S. Vogt) announced the discovery of a Saturn-sized planet around this Sun-like star using the Keck telescope in Mauna Kea, Hawaii (NASA announcement; exoplanets.org; and Marcy et al, 2000, in ps). The latest radial velocity measurements suggest that 79 Ceti has a companion "b" with at least 77 percent of Saturn's (23 percent of Jupiter's) mass (exoplanets.org). It moves around Star A at an average distance of 0.35 AUs (a semi-major axis inside the orbital distance of Mercury) in an elliptical orbit (e=0.21) that takes about 75.6 days to complete. (See an animation of the planetary and potentially habitable zone orbits of the 79 Ceti system, with a table of basic orbital and physical characteristics.)
Subsequent astrometric analysis, however, suggests that "planet b" may have as much as 111 times the mass of Jupiter with an inclination of 0.1° from Earth's line of sight (Han et al, 2001, in pdf). Thus, the "planet" could be a very dim red (M) dwarf stellar companion of 79 Ceti. The authors consider their analysis to be preliminary, needing confirmation with additional astrometric as well as other observations.
NASA -- larger image
Astrometry, however, suggests that 79 Ceti b may a very dim red
dwarf star, like Gliese 623 A (M2.5 V) and B (M5.8Ve) at lower right.
The orbit of an Earth-like planet (with liquid water) around 79 Ceti may be centered around 1.41 AUs -- within the inner reaches of the Main Asteroid Belt in the Solar System -- with an orbital period of 611 days (or 1.67 years). However, the eccentric orbit of "planet b" in with an average distance of 0.35 AUs could disrupt the orbital stability of an Earth-type planet in 79 Ceti's water zone, depending on the mass of this planetary or stellar companion. Astronomers would find it very difficult to detect an Earth-type planet in the water zone of this star using present methods.
Geoffrey W. Marcy, University
of California at Berkeley
The orbit of object "b" around
79 Ceti is only mildly eccentric,
but may still be more elliptical
than that of any planet in the
Solar System other than Pluto.
The following table includes all star systems known to be located within 10 light-years (ly), plus more bright stars within 10 to 20 ly, of 79 Ceti.
|Star System||Spectra &|
|BD-05 484||K4 V||5.0|
|BD-02 476||K0 V||6.3|
|* plus bright stars *||. . .|
|BD-08 547||G5 V||14|
|BD-01 316||G0 V||15|
|BD-06 594||G5 V||15|
|BD-01 293 AB||G2 V |
|HR 913 AB||G0 V-IV |
Try Professor Jim Kaler's Stars site for other information about 79 Ceti at the University of Illinois' Department of Astronomy. The late John Whatmough also created illustrated web pages on this system in Extrasolar Visions.
Up-to-date technical summaries on these stars can be found at: Jean Schneiders's Extrasolar Planets Encyclopaedia; the Astronomiches Rechen-Institut at Heidelberg's (ARICNS; the HIPPARCOS Catalogue using the VizieR Search Service mirrored from the Centre de Données astronomiques de Strasbourg (CDS); NASA's ADS Abstract Service for the Astrophysics Data System; and the SIMBAD Astronomical Database mirrored from CDS, which may require an account to access.
In Greek mythology, Cetus is supposed to be the sea monster that would have devoured the "chained maiden," Andromeda, if Perseus had not come to the rescue. For more information on stars and other objects in Constellation Cetus, go to Christine Kronberg's Cetus. For an illustration, see David Haworth's Cetus.
For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.
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