Epsilon Eridani (ε Eri, ε Eridani) is a main-sequence star of spectral class K2. Only 10.5 light years (ly) away, it is the closest star in the constellation Eridanus, as well as the third closest star system visible to the naked eye. Its age is estimated at less than a billion years. Because of its relative youth, Epsilon Eridani has a higher level of magnetic activity than the Sun, with a stellar wind 30 times as strong. Its rotation period is a relatively rapid 11.2 days, although this varies by latitude. Epsilon Eridani is both smaller and less massive than the Sun, with a lower enrichment of elements other than hydrogen or helium.
The motion of this star along the line of sight to the Earth, known as the radial velocity, has been observed for more than twenty years. This data yields evidence of a gas giant planet orbiting Epsilon Eridani, making it the nearest extrasolar system with a candidate exoplanet. This unconfirmed object, conventionally known as Epsilon Eridani b, was formally announced in 2000 by a team of astronomers led by Artie Hatzes. However, the radial velocity data contain a high level of background noise due to the star's magnetic activity, and the existence of the proposed planet is not universally accepted. Current data indicate that the planet orbits in a period of about 7 years at a mean separation of 3.4 astronomical units (AU), corresponding to 505 million kilometers.
The system includes two debris belts composed of rocky asteroids; one at about 3 AU and the second at about 20 AU, whose structure may be maintained by a hypothetical second planet, Epsilon Eridani c. In addition, Epsilon Eridani harbors an extensive outer debris disk corresponding to the Solar System's Kuiper belt.
As one of the nearest Sun-like stars, Epsilon Eridani regularly appears in science fiction. The nearby star Luyten 726-8 will have a close encounter with Epsilon Eridani in about 31,500 years when they will be separated by about 0.93 ly.
In 1960, Philip Morrison and Giuseppe Cocconi proposed that extraterrestrial civilizations may be using radio signals for communication. Project Ozma, headed by Frank Drake, used a radio telescope at Green Bank, West Virginia to search for such signals. Its targets were the nearby Sun-like stars Epsilon Eridani and Tau Ceti. They were observed at the emission frequency of neutral hydrogen, 1420 MHz, for a total of 150 hours over four months. However, no signals of intelligent extraterrestrial origin were detected. The experiment was repeated by Frank Drake in 2010, with the same negative result.
In Habitable Planets for Man, a 1964 RAND Corporation study by Stephen H. Dole, the odds of a habitable planet in orbit around Epsilon Eridani were estimated as 3.3%. For the purpose of the study, a habitable planet was defined to be an Earth-like planet that has the physical properties thought necessary for complex life forms to have evolved. Among the known stars within 22 ly, it was listed with the 14 stars that were thought most likely to have a habitable planet.
A new strategy in the search for extraterrestrial intelligence (SETI) was proposed by William I. McLaughlin in 1977. He suggested that widely observable events such as novae explosions may be used by intelligent extraterrestrials to synchronize the transmission and reception of their signals. To test this concept, during a six month period in 1988 Epsilon Eridani was observed using a 40-foot radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia, with Nova Cygni 1975 being used as the timer. However, no anomalous radio signals were observed.
Based on its location within 7.2 pc, Epsilon Eridani was among the target stars of Project Phoenix, a 1995 microwave survey for signals from extraterrestrial intelligence. By 2004 Project Phoenix had checked about 800 stars, but had not yet detected an unimpeachable signal.
Epsilon Eridani in space opera:
- In Gordon Dickson's? Childe Cycle? (1959-1988) the Friendly worlds of Harmony? and Association? orbit Epsilon Eridani.
- 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).
- In Larry Niven's 1973, Hugo Award nominated, Protector, Epsilon Eridani's earth-like planet, Home, is colonized and inhabited by humans. Epsilon Eridani and Home also appear in Niven's collection of Known Space novels and short stories.
- In the Honor Harrington book series (1993-) by David Weber?, Epsilon Eridani is one of the oldest Solarian League? worlds.
- 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 system also includes a moon around Yellowstone called Marco's Eye?, and a gas giant planet called Tangerine Dream?.
- In Halo: Reach, Halo: The Fall of Reach, and Halo: First Strike, large portions of the stories take place on a planet called Reach?, which orbits Epsilon Eridani. It is also mentioned that there are three other planets orbiting Epsilon Eridani: Circumstance?, Tribute?, and Beta Gabriel?.
- In C. J. Cherryh's Alliance-Union Universe, it is the location of Viking Station.
- In the television series Babylon 5?, the titled space station? orbits the third planet (Epsilon 3) in this system.
- In the anime series The Super Dimension Cavalry Southern Cross?, the planet Glorie? is stated to be in the Epsilon Eridani system.
- In the TV Series Space: Above and Beyond?, the first encounter with the hostile Chigs occurred at the Vesta Colony?, the first human extrasolar colony, which orbited Epsilon Eridani.
- 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.
- 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?).
- In the GDW's 2300 AD?, Dukou? is the first planet of Epsilon Eridani, an habitable but glacial world. Epsilon Eridani is the main access to the Latin systems.
- In the Star Trek? franchise, Epsilon Eridani was once suggested as a possible location of the planet Vulcan, and was listed as such in the Star Trek Spaceflight Chronology. Canon Star Trek later confirmed 40 Eridani as the Vulcan? star system, but Epsilon Eridani was established as the location of Axanar? in Star Trek Star Charts.
- Escape Velocity game by Ambrosia Software. System of the planet Tabletop is called Eridani.
- In Dune Universe it is the system of planet Richese.