Counter-Earth

The Counter-Earth (from the Greek Antichthon, ὰντὶ = against and χθών = earth) is a hypothetical Earth-like body in the cosmological model of the ancient Greek philosopher Philolaus. There are also the modern idea that there could be an undiscovered planet, the same orbit around the Sun as the Earth has, however, is on the opposite side of the Earth at the Lagrange point L3 behind the sun. The existence of such a planet is now ruled out.

The concept of a Counter-Earth is also used in modern science fiction literature more frequently.

• 2.1 Problems of thesis

The Counter-Earth Philolaos

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The Pythagorean philosopher Philolaus taught in the second half of the 5th century BC, that there was a " central fire ", which is the core and center of gravity of the universe. All things would be attracted to this center and all heavenly bodies revolved around it. On the innermost orbit around the central fire earth revolves counter adopted. This is followed ( from inside to outside ) Earth, Moon, Sun, Mercury, Venus, Mars, Jupiter, Saturn, and quite outside the sphere of fixed stars. In its orbit around the central fire, the ( imaginary as flat ) earth synchronous rotation, so that it always turns to the central fire the same page. The central fire is for the people thus always "down" and invisible, as the inhabited side of the planet is always facing away from the central fire. The Counter-Earth was introduced by Philolaus of balance reasons to counterbalance the earth. This had the following background: the Greek philosophers, the planet as presented "light, ethereal " objects before. The earth, however, consisted of earth and water and was undoubtedly a "heavy" body. If the Earth orbits the only heavy celestial bodies, the central fire, that would be the focus of the universe no longer the focus. However, since this is the point around which everything revolves, Philolaus ' model required a second body, which balances the imbalance caused by the Earth: the Counter-Earth.

Aristotle criticized this system because it was not based on appearances, but by preconceived notions; the Counter-Earth was only introduced in order to bring the number of moving bodies in the sky to ten, since this number was considered to be perfect. Aristotle also rejected the thesis of the " central fire" and advocated instead the geocentric worldview, in which the earth rests in the center of the universe and all celestial bodies orbiting around it.

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Alexander von Humboldt is an example for the interpretation of counter- earth as representing itself " within 24 hours to the central fire moving ... opposite hemisphere, the antipodes - half of our planet. " Philolaus ' successor Hicetas of Syracuse, Ekphantos and Heraclides Ponticus " also " the idea of ​​the self-rotation of the earth.

Adaptation of the thesis

In the heliocentric world view, whose roots also lie in ancient times and the generally prevailed in Europe especially during the Renaissance, do all the planets, including the earth, the sun. A hypothetical counter- earth, which orbits the sun on the same orbit as the Earth, but opposite to the earth, would be seen from earth always stand behind the sun and would thus never visible.

Joseph -Louis Lagrange calculated that there are five points in the three-body problem, in which a body with a small mass is force-free. One called by these five points, L3, is located in the Sun-Earth system always such a position and would thus possible physical place for a previously undiscovered planet.

Through these considerations, the assumption was that such a Counter-Earth existed, at least as theoretically conceivable hypothesis hold isolated until well into the modern era.

Problems of the thesis

Such a planet actually existed, he would always hidden behind the sun. He would, however, still due to its gravitational influence detectable from the Earth to the other planets of the solar system. There was no such effect noted and space probes to the planets Venus, Mars, and other places would not have arrived at their destination, if a Counter-Earth existed, as just such an effect was not included in the calculation of the flight path. In addition, the rotational velocity of the earth varies slightly due to its elliptical orbit. A Counter-Earth would therefore be very precise in a particular orbit are to constantly remain behind the sun.

The orbit of a Counter-Earth would also be unstable in a geologically short period of time and would migrate away from the exact opposite position to the earth. This would mean that the two planets either crashed or very near vorbeiflögen each other, which would cause both planets would be thrown out of their previous orbit.

The Counter-Earth in science fiction

In science fiction literature, the concept of Counter-Earth is occasionally taken.

• In Gor - cycle by John Norman
• In the series Space partisans of Nikolai von Michalewsky
• In the movie accident in space

The second Earth

To be distinguished from the Counter-Earth is a possible second Earth, ie an Earth-like planet discovered among previously around 450 and other suspected exoplanets beyond the solar system.