Could there be an unseen planet on the other side of the Sun?

Asked by: James Masters, East Grinstead

The idea that there might be another planet in our Solar System on an orbit that keeps it permanently behind the Sun dates back at least 2400 years to the Greek philosopher Philolaus. He postulated the existence of a ‘counter-Earth’ called Antichthon. It’s also caught the imagination of science fiction writers, including Gerry Anderson of Thunderbirds fame, who madea film based on the ideain the late 1960s.忧郁症andAnother Earth, both from 2011, also explore these themes.

Sadly, the science doesn’t stack up: the gravitational action of the other planets in the Solar System would distort Antichthon’s orbit until it came out of perfect alignment with the Earth. Astronomers also have very precise data on the position of the planets and space-probes, and they show no evidence of missing planets.

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