Thousands of years ago, an idea was proposed that there could be another planet in our Solar System on the part of our orbit which keeps it permanently hidden by the Sun.
Earth's Unseen Twin
The theory dates back at least 2,400 years to the Greek philosopher Philolaus. He postulated the idea of a 'counter-Earth' which he called Antichton. This concept also caught the imagination of science fiction writers, such as Gerry Anderson who made a movie based on this theory in the late 1960s.
The counter-Earth theory suggests a view of the Solar System where the Earth and the Sun rotate around an unseen "central fire" with Antichthon on the other side. This hidden planet is also believed to cast its shadow on the Moon.
Although the theory seems strange today, it was likely made as a way to explain the existence of lunar eclipses. According to Aristotle, some lunar eclipses were caused by the interposition of this counter-Earth. Another reason that this postulate gained some support from Greek intellectuals was that the counter-Earth brought the total moving count up to ten, a number that is pleasing to the Pythagoreans.
The theory died away as more advanced astronomical tools allowed scientists to move away from the geocentric view of the Solar System. In modern times; however, this idea has sometimes reared its head as a conspiracy theory.
READ ALSO: Trojan Planets Co-Existing in the Same Orbit Spotted After Being Hypothesized for 20 Years
Can Two Planets Share the Same Orbit?
Surprisingly, this kind of orbit is possible, although it would exist on a distant planetary system. The first evidence of such double worlds was discovered by a team of Spanish scientists led by Olga Balsalobre-Ruza from the Center of Astrobiology in Madrid.
The discovery was reported on July 19, 2023 after a telescope in Chile allowed the team to view the young planetary system PDS 70. The planet PDS 70b was seen traveling in the same orbit as a cloud of debris which could be evidence of another planet. Known as 'Trojan planets,' the twin planets might have similar conditions given that they share the same duration of the year and habitability conditions.
The existence of such worlds cannot happen in our Solar System. Just because we cannot directly see the other side of the Sun does not mean we do not know what is happening back there.
Astronomers detect planets by how they influence other celestial bodies. For instance, Neptune was discovered when scientists realized that the orbit of Uranus was influenced by an unknown world beyond it.
In the case of the counter-Earth theory, the gravitational influence of the other members of the Solar System would affect the orbit of Antichthon until it came out of perfect alignment with our planet. Additionally, when astronomers obtained precise data on the position of the planets and space probes, they did not find any evidence of missing planets.
Aside from this, a counter-Earth would likely affect the motions of all nearby cosmic objects. For instance, Venus approaches our planet as close as 25 million miles (40 million kilometers) every 584 days, so it can get very close to the counter-Earth at that distance. The mass of Venus would also have a gravitational influence on Antichthon enough to move it to a position where we can view it directly.
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