82 Eridani

JPL, CalTech, NASA


Larger illustration


Astronomers have identified
82 Eridani as a prime target
for the Terrestrial Planet Finder
(TPF), now planned for launch
between 2014 and 2020.

82 Eridani

This main sequence, yellow-orange dwarf of spectral and probable luminosity type G5-8 V (Perrin et al, 1977, page 782; Haisch and Basri, 1985, pages 180-181; and Olin Jeuck Eggen, 1956, page 463; and 1955, No. 703 in page 402) may have 97 percent of Sol's mass (RECONS), 92 percent of its diameter (Johnson and Wright, 1983, page 653), about 60 percent of its luminosity. The star appears to be less enriched in elements heavier than hydrogen ("metals") because it has between 29 and 100 percent of Sol's abundance of iron (Cayrel de Strobel et al, 1991, page 280). The star also shows a radial velocity of about 52 miles per second (mps) -- about 84 km per second or kps -- in recession, but the true space velocity is about 80 mps (about 129 kps). Indeed, 82 Eridani's low metallicity and high space velocity, and its substantial galactic orbital eccentricity (e= 0.40) suggest that it may be more than 10 billion years old (see Table 1 for HD 20794 in Olin Jeuck Eggen, 1998 (1919-1998); and John B. Hearnshaw, 1973), although it does appear to have a slight overabundance of metals for its age. Since the star's orbit lies primarily within the galactic plane (as does Sol's own orbit), it is thought to be an old disk star.

82 Eridani was once thought to be unusually bright for its spectral type. The star was the brightest dwarf in a 1964 catalogue of high velocity stars with space motions exceeding 100 kps (62 mps) collected by Olin Jeuck Eggen (1919-1998). In the past, it was sometimes classified as a giant (1982 Bright Star Catalogue, 4th Edition; and Slee et al, 1989) or a subgiant star -- evolving off the main sequence as it begins to fuse the increasing amounts of helium "ash" mixed with hydrogen at its core. Moreover, the star has been called e Eridani, presumably because it was suspected of variability. Some useful catalogue numbers for this star are: e Eri, 82 Eri, HR 1008, Gl 139, Hip 15510, HD 20794, CD-43 1028, CP(D)-43 354, SAO 216263, FK5 119, LHS 19, LTT 1583, LFT 277, and GC 4000.

82 Eridani B?

[No data are available on this possible spectroscopic companion at this time.]

Hunt for Substellar Companions

No large substellar companion has been found thus far (Murdoch et al, 1993). However, the distance from 82 Eridani A where an Earth-type planet would be "comfortable" with liquid water is centered around 0.80 AU -- midway between the orbital distances of Venus and Earth in the Solar System. At that distance from the star, such a planet would have an orbital period of almost 275 days, or over two thirds of an Earth year. Astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around 82 Eridani. As currently planned, the TPF will include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning in 2015.