Orbit Unlimited
Encyclopedia
Orbit Unlimited is a science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...

 novel by Poul Anderson
Poul Anderson
Poul William Anderson was an American science fiction author who began his career during one of the Golden Ages of the genre and continued to write and remain popular into the 21st century. Anderson also authored several works of fantasy, historical novels, and a prodigious number of short stories...

, first published in 1961. Essentially a linked group of short stories, it recounts the colonisation of the planet Rustum, a fictional terrestrial world orbiting Epsilon Eridani
Epsilon Eridani
Epsilon Eridani is a star in the southern constellation Eridanus, along a declination 9.46° south of the celestial equator. This allows the star to be viewed from most of the Earth's surface. At a distance of 10.5 light years , it has an apparent magnitude of 3.73...

, by a group of refugees from an authoritarian planet Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. Although habitable, Rustum's atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 is so great that only its mountains and high plateaus are suitable for human settlement. The novel, like much of Anderson's work, has a libertarian
Libertarianism
Libertarianism, in the strictest sense, is the political philosophy that holds individual liberty as the basic moral principle of society. In the broadest sense, it is any political philosophy which approximates this view...

 subtext as the colonists flee the oppression on their home planet.

Science background

Although Anderson had no way of knowing this at the time of writing, a planet is now known to orbit around Epsilon Eridani
Epsilon Eridani
Epsilon Eridani is a star in the southern constellation Eridanus, along a declination 9.46° south of the celestial equator. This allows the star to be viewed from most of the Earth's surface. At a distance of 10.5 light years , it has an apparent magnitude of 3.73...

, a star only 10.5 light years from earth. It is a gas giant, similar to Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

, and orbits its star at a distance of 3.2 A.U. every seven years. Gravitational irregularities show that at least one other planet orbits the star.

However, as a character mentions in the novel (pg. 17 of the 1972 Pyramid paperback edition), Epsilon Eridani was not the location of Rustum. Instead, Anderson chose the star Epsilon Eridani (now known as 82 Eridani) as Rustum's host star. 82 Eridani is 19.8 light years
Light Years
Light Years is the seventh studio album by Australian recording artist Kylie Minogue. It was released on 25 September 2000 by Parlophone and Mushroom Records. The album's style was indicative of her return to "mainstream pop dance tunes"....

 distant, categorized in the G5 stellar spectral class with approximately 97% of the mass of the Sun and 60% of its luminosity. 82 Eridani is listed as one of the "top 100" targets of NASA's proposed Terrestrial Planet Finder
Terrestrial Planet Finder
The Terrestrial Planet Finder was a proposed project by NASA to construct a system of telescopes for detecting extrasolar terrestrial planets. TPF was postponed several times and finally cancelled...

mission.
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