Sunday, July 8, 2007

Epsilon Eridani

Star type
g K3-5 Ve (main sequence, orange-red dwarf)

Distance from Earth
g 10.5 ly (nearest extrasolar planet to our solar system)

Star Service No.
g NA

g About 850 million years

Diameter/Mass/Temp (xSol)
g 84%; 83%-85%; 5100 K

Brightness (xSol)
g 28%

g Relatively low metallicity, particularly in iron.

Comparison to Sol
g See chart (similar to GJ 205 and GJ 887)

Picture of star
g See picture
g See illustration at upper right (graphic courtesy of NASA/JPL-Caltech)

Star system features
g System consists of three dust rings. The inner ring is a virtual twin to Earth's asteroid belt and is about the same distance at 3 AU. The middle ring is at about 20 AU, or where Uranus is located in our solar system; this ring contains about as much mass as the Moon. The outer, icy ring stretches from 35 to 100 AU; it has about 100x more material than the Kuiper Belt.

Known planets
The presense of three asteroid/dust rings implies that unseen planets (which are confining and shaping the rings). The three planets would range in size from Neputune to Jupiter. A candidate planet (see Planet A below) already hass ben detected near the inner ring. The second planet would lurk near the second ring (see Planet B below). The third planet (see Planet C below) would orbit at about 35 AU near the inner edge of the outer ring.
g Planet A: Jupiter-like planet around star; about 1.2 (+/- 0.3) times Jupiter' and an orbital distance of about 3.3 AUs - within the outer region of the Main Asteroid Belt in the Solar System; it circles the star in a highly elliptical orbit (e= 0.6) that takes about 6.85 Earth years to complete, varying in orbital distance from 1.3 to 5.3 AUs.
g Planet B: A planet about 1/10 of Jupiter’s size, orbiting the star every 280 years, likely lurks near the second ring at about 20 AU. This yet unseen planet prevents formation of planets in the habitable zone.
g Planet C: A planet with a fifth of Jupiter's mass may orbit at 35 AU from the star. From moons around this planet, one could see the zodiacal light glowing from a secondary disc orbiting the star (Epsilon Eridani B); the outer dust ring encircling Epsilon Eridani forms an arc across the sky.

Habitable zone
The distance from Epsilon Eridani where an Earth-type rocky planet may have liquid water on its surface may have to be between 0.47 and 0.91 AU (Jones and Sleep, 2003) - between the orbital distances of Mercury and Earth in the Solar System. In that distance range from the star, such a planet would have an orbital period shorter an Earth year. Given the apparent youth of this star system, however, it is likely that only primitive, single-celled organisms like bacteria that can survive heavy meteorite or cometary bombardment would be likely to survive on any Earth-type planet that has cooled sufficiently to allow carbon-based lifeforms to develop. (For an illustrated discussion, see Christoph Kulmann's web page on the potential habitable zone around Epsilon Eridani. Also, see an orbital depiction of the center of the habitable zone of this system, with a table of basic orbital and physical characteristics.) As gas giant’s orbit is elliptical and eccentric, an Earth-like planet appears unlikely. In any case, star system probably is too young to boast a planet with an oxygen atmosphere. Probability of a habitable planet: 3.3%.

Orbital map
g See map

View from star
g See sky map

Nearby stars
(Star systems with 10 light years)
g Hip 15689, 4.1 ly
g Luyten 726-8, 5.1 ly
g Tau Ceti, 5.5 ly
g Teegarden's Star, 5.8 ly
g Omicron2 Eridani 3, 6.4 ly
g LHS 1565, 6.9 ly
g YZ Ceti, 7 ly
g Sirius AB, 7.8 ly
g L 1159-16, 8 ly
g (LP 944-20) (brown dwarf) 8.3 ly
g Kapteyn's Star, 8.5 ly
g LP 656-38, 9 ly
g Ross 614 AB, 9.4 ly
g Van Maanen's Star, 9.9 ly

Map locating star system
g See 20ly map
g See 47ly map

Location in Earth sky
g In the northeastern part of Constellation Eridanus, the River -west of Rana (Delta Eridani) and northwest of Zaurak; clearly visible to the naked eye as the third closest star viewable without a telescope; clearly visible to the naked eye as the third closest star viewable without a telescope

Other names
g EPS Eri; HR 1084; Gl 144; HD 22049

Sci-fi mentions
g In Gordon Dickson's Childe Cycle (1959-1988) the Friendly worlds of Harmony and Association orbit Epsilon Eridani.
g In the robot novels of Isaac Asimov, it is the sun of the first world of the second wave of settlers: Comporellon (Foundation's Edge, 1982) or Baleyworld (Robots and Empire, 1985).
g In Greg Bear's Eon (1985), Epsilon Eridani is the original destination of the Thistledown.
g In the Viagens Interplanetarias stories of L. Sprague de Camp its system contains the inhabited planets of Thor and Kukulkan, the later being the setting of his novels The Stones of Nomuru (1988) and The Venom Trees of Sunga (1992).
g In the Honor Harrington book series (1993-) by David Weber, Epsilon Eridani is one of the Solarian League worlds, and the source of the Eridani Edict, which sprang from the Epsilon Eridani Massacre where 7 billion people were killed by orbital bombardment.
g In the Worldwar books (1994-1996) by Harry Turtledove, Epsilon Eridani is one of the subject star systems (Rabotev) of The Race.
g In the Revelation Space universe (2000-), encompassing five novels, two novellas, and eight short stories by author Alastair Reynolds, the Epsilon Eridani system includes a planet called Yellowstone that is the most important planet in the series and is home to the most advanced human civilization for about three hundred years. The Yellowstone society is centered in the Glitter Band system of habitats in orbit around Yellowstone and in Chasm City, located on the planet's surface in a domed crater. The system also includes a moon around Yellowstone called Marco's Eye, and a gas giant planet called Tangerine Dream. Among he novellas/short stories is "Galactic North"
g In the fictional Star Trek universe, it is considered by some fans to be the location of the planet Vulcan, the home of Mr. Spock. 40 Eridani is also commonly suggested. That Epsilon Eridani could be Vulcan's home star is contradicted by statements of Commander Tucker on "Star Trek: Enterprise," where he states that Vulcan is 16 light years from Earth; 40 Eridani is given as the location by the authorized book "Star Trek: Star Charts" (Pocket Books, 2002). "Star Charts" lists the star system as Axanar, home to an androgynous humanoid species with an average life span of 400 years, mentioned in "Star Trek: Enterprise" episode "Fight or Flight."
g In the television series Babylon 5, the space station itself orbits the third planet (Epsilon 3) in this system.
g Gerry Anderson's television show Space Precinct is set on a planet in the "Epsilon Erandi" system, which may be an error for Epsilon Eridani.
g In the Battletech universe Epsilon Eridani is one of the worlds closest to Terra. It was originally a member-world of the Terran Hegemony. The planet passed into Capellan control after the collapse of the Star League. It was conquered by the Federated Suns during the 4th Succession War, and remained under the control of the Federated Suns, later the Federated Commonwealth, until 3057, when the world became independent in the aftermath of the conflict between the Federated Commonwealth and an alliance between the Capellan Confederation and the Free Worlds League.
g In the video game series Halo, the planet Reach is in this system. Reach is a military stronghold, a shipyard, and the site of the SPARTAN project which produced Master Chief. The planet was bombarded from orbit and made uninhabitable on August 30, 2552.
g In the game Face of Mankind there's a space colony on one of the ice planets orbiting Epsilon Eridani.
g In the Alternate Reality Game The Beast, Epsilon Eridani is mentioned as the destination of rogue space-faring AIs, and therefore the birthplace of the advanced androids seen at the end of the movie A.I., which the game was promoting.
g In the Frontier-series of games (including Frontier: Elite II and Frontier: First Encounters), Epsilon Eridani is a system dedicated to luxury-class and adult tourism (primarily directed towards the terraformed planet known as New California). The system does not come under Federal law, despite being deep in the core of the Federation. As a result, narcotics and slavery are quite legal here and does brisk business as a major import. Like most other systems, military-grade weaponry and nerve gas are illegal here.
g Among the first 26 interstellar expeditions is one to this star system in Frederick Pohl's short story "Father of the Stars"
g The Narrat slaughtered a human colony in this star system in novel “Ace of Aces” by Chris Berman

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