Epsilon Reticuli

© Torben Krogh & Mogens Winther,

(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)

Epsilon Reticuli is an orange-red
star, somewhat similar to Epsilon
Eridani at left center of meteor.
(See a Digitized Sky Survey image
of Epsilon Reticuli from the Nearby Stars Database.)

System Summary

Epsilon Reticuli is located about 59.5 light-years from Sol. It lies in the northeastern corner (4:16:29.0-59:18:7.8, ICRS 2000.0) of Constellation Reticulum, the Reticule or Net (an old astronomical instrument used to measure star positions) -- north of Alpha Reticuli, and southwest of Alpha Doradus. On December 11, 2000, astronomers announced the discovery of a large planetary companion to this star in a stable highly circular orbit just beyond one AU out from the star -- unlike the previously discovered "torch" Jupiters (see press release and exoplanets.org, with more details below). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

The Star

Epsilon Reticuli is an orange-red star of spectral and luminosity type K1-2 IVa-III. It appears to be a highly evolved subgiant or giant star. The star may have 1.2 times Sol's mass (exoplanets.org; and Randich et al, 1999), 6.6 times its diameter (Johnson and Wright, 1983, page 655), and 4.6 times its luminosity. The star appears to be around 1.7 times as enriched as Sol with elements heavier than hydrogen ("metallicity"), based on its abundance of iron (exoplanets.org; and Randich et al, 1999). It may be around 10 billion years old -- more than twice Sol's 4.6 billion years. Useful catalogue numbers and designations for the star include: Eps Ret, HR 1355, Gl 167.3, Wo 9153, Hip 19921, HD 27442, CP(D)-59 324, and SAO 233463.

The orbit of an Earth-like planet with surface water would be centered within 2.2 AU -- between the orbital distances of Mars and the Main Asteroid Belt in the Solar System -- and take within 2.9 years to complete. However, the giant planetary companion "b" recently discovered around Epsilon Reticuli would probably disturb such an orbit. Astronomers would find it very difficult to detect an Earth-sized planet around this star using present methods.

Planet "b"

NASA

Cassini-Huygens Mission
to Saturn and Titan

Larger image.

Planetary candidate "b" appears to
be a gas giant somewhat larger than
Jupiter (shown here with Europa).

On December 11, 2000, a team of astronomers (including Chris G. Tinney, Hugh R. A. Jones, Alan J. Penny, Kevin Apps, R. Paul Butler, Geoffrey W. Marcy, Steven S. Vogt, and Gregory W. Henry) announced the discovery of a planetary companion "b" with a minimum mass of 1.17 that of Jupiter (Butler et al, 2001; in ps), with a similar diameter. The planet moves around Epsilon Reticuli with an average separation of 1.16 AUs, which would be between the orbital distance of Earth and Mars in the Solar System. Its orbit has a very low eccentricity (e= 0.06) which takes 418 days or 1.13 years to complete (exoplanets.org). (See an animation of the planetary and potentially habitable zone orbits of this system, with a table of basic orbital and physical characteristics.)

Closest Neighbors

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 Epsilon Reticuli.

Star System	Spectra & Luminosity	Distance (light-years)
CP-63 231	K5 V	9.3
L 178-49	M V	9.7
* plus bright stars *		. . .
CP-60 424	G5 Ve	11
Gamma Doradus	F4 III	11
Kappa Reticuli AB	F5 V-VI M V	13
CP-65 475	K1 V-IIIp	14
Beta Pictoris	A3 V	17
CD-56 1071 AB	G5 V M V	15
Iota Horologii	G0 Vp	16
HR 1294	G3 V	17

Other Information

The late John Whatmough 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, and the Nearby Stars Database. Additional information may be available at Roger Wilcox's Internet Stellar Database and from www.alcyone.de's entry for HR 1355.

Constellation Reticulum is one of those obscure constellations in the Southern Hemisphere invented in the mid-1880s by the Abbé [Abbot] Nicholas Louis de La Caille (1713-1762), who had the great honor of naming 15 of the 88 constellations by becoming the first astronomer to systematically observe the entire night sky. La Caille originally called this group of stars the "Reticulum Rhomboidalis" for the shape defined by some of the constellation's brightest stars, as a reticle is a grid or system of lines in an eyepiece that helps in the centering of focusing instruments, such as a sextant, on a particular object. However, the brightest star of small and dim Reticulum is of only 3rd magnitude. It is located between constellations Dorado (north-east), Horologium (north-west), and Hydrus. For more information about the stars and objects in this constellation, go to Christine Kronberg's Reticulum. For illustration, see David Haworth's Reticulum.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.