Against earth

Alleged position of the counter-earth in the solar system (shown as Gor )

The counter- earth (from the Greek Antichthon , ἀντὶ "against" and χθών "earth") is a hypothetical earth-like body in the cosmological model of the ancient Greek philosopher Philolaos . There is also the modern idea that there could be an undiscovered planet that has the same orbit around the sun as the earth , but is on the opposite side of the earth at Lagrange point L ₃ behind the sun. The existence of such a planet is now considered impossible.

The concept of a counter-earth is also more common in modern science fiction literature.

The counter-earth at Philolaos

Sketch from Dante and the Early Astronomers by MA Orr, 1913.

10. Body

The Pythagorean philosopher Philolaos taught in the second half of the 5th century BC that there was a "central fire" that forms the center and center of gravity of the universe. All things would be attracted to this center and all heavenly bodies orbit it. The assumed counter-earth circles on the innermost orbit around the central fire. This is followed (from the inside out) earth, moon, sun, Mercury, Venus, Mars, Jupiter, Saturn and on the very outside the sphere of fixed stars. As it revolves around the central fire, the earth (imagined as flat) has a bound rotation, so that it always faces the central fire on the same side. The central fire is therefore always "below" and invisible to people, since the inhabited side of the earth is always turned away from the central fire. The counter- earth was introduced by Philolaos as a counterweight to the earth for reasons of balance . This had the following background: The Greek philosophers imagined the planets as "light, ethereal" objects. The earth, on the other hand, consisted of earth and water and was therefore undoubtedly a "heavy" body. If the earth as the only heavy celestial body orbits the central fire, the center of gravity of the universe would no longer be in the center. But since this is the point around which everything revolves, Philolaos' model needed a second body that balances this imbalance caused by the earth: the counter-earth.

Aristotle criticized this system because it was not based on appearances but on preconceived notions; The counter-earth was only introduced to bring the number of bodies in motion in the sky to ten, since this number was considered perfect. Aristotle also rejected the thesis of the “central fire” and instead advocated the geocentric view of the world , in which the earth rests in the center of the world and all celestial bodies orbit it.

Underside of the earth

Alexander von Humboldt is exemplary for the interpretation of the Counter-Earth than to "within 24 hours to the central fire moving [...] opposite hemisphere, the antipodes -Hälfte our planet." Philolaus' successor Hicetas , Ecphantus the Pythagorean and Heraclides Ponticus "also" represented the idea of the earth's own rotation.

Adaptation of the thesis

Lagrange points

In the heliocentric view of the world , which also has its roots in antiquity and which became generally accepted in Europe, especially during the Renaissance, all planets, including the earth, orbit the sun. A hypothetical counter-earth orbiting the sun on the same orbit as the earth, but opposite to the earth, would always be behind the sun when viewed from the earth and would therefore never be visible.

Joseph-Louis Lagrange calculated that there are five points in the three-body problem in which a body with small mass is force-free. One of these five points, called L ₃ , is always in such a position in the sun-earth system and would therefore be a physically possible location for a previously undiscovered planet.

Through these considerations, the assumption that such a counter-earth existed, at least as a theoretically conceivable hypothesis, could still be held up to modern times.

Problems of the thesis

If such a planet actually existed, it would always be hidden behind the sun. However, it would still be detectable from Earth due to its gravitational influence on the other planets of the solar system. No such influence was found and space probes to the planets Venus , Mars and other locations would not have reached their destination if a counter-earth existed, as such an influence was not included in the calculation of the flight path. In addition, the orbital speed of the earth varies slightly due to its elliptical orbit. A counter-earth would have to be very precisely in a certain orbit in order to stay behind the sun.

The orbit of a counter-earth would also be unstable in a geologically relatively short period of time and would migrate away from the exact opposite position to the earth. This would cause the two planets to either collide or fly very close to each other, which would result in both planets being thrown out of their previous orbit.

The counter-earth in science fiction

In science fiction literature, the concept of counter-earth is occasionally taken up, e.g. B .:

In the Gor cycle by John Norman
In the series Space Partisans by Nikolai von Michalewsky
In the film accident in space
In the film Gamera versus Guiron - Frankenstein's monster battle in space
In the children's book Urmel flies into space by Max Kruse (Planet Arutuf (backwards from Futura ))
In the science fiction drama Another Earth , a planet approaches the earth that resembles it in almost all features (such as continents and the people who live there).

The second earth

To be distinguished from the counter-earth is a possible second earth, i.e. H. an earth-like planet among the exoplanets beyond the solar system.

literature

Petra Hartmann : The dream of the tenth planet. A short history of the counter-earth in philosophy, film and fantasy. Epilogue to: Mark Brandis : Der Spiegelplanet. Nittendorf, Wurdack 2010. pp. 163-190.

Web links

The Pythagoreans. Drury University, archived from the original on January 14, 2010 ; accessed on May 9, 2016 .
Florian Freistetter: The counter-earth. scienceblogs.de, May 9, 2016, accessed May 9, 2016 .

Individual evidence

↑ Alexander von Humboldt: Kosmos. Draft of a physical description of the world. Reprint, Frankfurt am Main 2004, p. 552, (online) @ projekt-gutenberg.org - referring to August Böckh : Philolaos des Pythagoreer teachings. Berlin 1819, p. 117 (PDF, 11.87 MB) @ edoc.hu-berlin.de; in this model, the central fire, also called hestia , is responsible for the geothermal energy of the hot springs and vapors, e.g. B. in the altar of Hestia in Delphi , see u. a. AMC Sengör: The Large-Wavelength Deformations of the Lithosphere: Materials for a History of the Evolution of Thought from the Earliest Times to Plate Tectonics. Boulder, Colorado 2003, p. 37 (accessed March 19, 2014)

[1] Alexander von Humboldt: Kosmos. Draft of a physical description of the world. Reprint, Frankfurt am Main 2004, p. 552, (online) @ projekt-gutenberg.org - referring to August Böckh : Philolaos des Pythagoreer teachings. Berlin 1819, p. 117 (PDF, 11.87 MB) @ edoc.hu-berlin.de; in this model, the central fire, also called hestia , is responsible for the geothermal energy of the hot springs and vapors, e.g. B. in the altar of Hestia in Delphi , see u. a. AMC Sengör: The Large-Wavelength Deformations of the Lithosphere: Materials for a History of the Evolution of Thought from the Earliest Times to Plate Tectonics. Boulder, Colorado 2003, p. 37 (accessed March 19, 2014)