Astronomers and amateur ‘Planet Hunters’ discover planet PH1, detected in a quadruple star system

Artist's concept of planet PH1 (Haven Giguere/Yale University)While studying astronomy, I used to pester my professors with questions based on my love of science fiction. One I remember asking was: "Can planets form in star systems that have more than one star?" The answer given to me at the time was that it was possible around a 'close binary' system — where two stars orbit each other very close together — because any planets that formed would just orbit around both of the stars as if they were one, larger star. However for 'far binary' systems — with two or more stars that orbit at far distances to each other — it was unlikely because any planetary bodies that tried to form in the system would be pulled at by the two (or more) stars' gravitational forces in such a chaotic, ever-changing way that they would never survive, especially in orbits between the two stars.

I accepted that answer (as disappointing as it was at the time), but it would seem that my disappointment was unnecessary.

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Assisted by a group of citizen scientists called Planet Hunters, an international team lead by researchers at Yale University have discovered and confirmed the first planet to be detected in a quadruple star system. This specific star system is a 'dual-binary' star system, with one pair of binary stars orbiting each other at the centre of the star system, and another pair orbiting each other close together, and orbiting the first pair at a distance of nearly 150 billion kms (for reference, that's over 20 times the farthest distance of Pluto's orbit from our Sun).

The planet — called PH1 — is a roughly Neptune-sized planet that is orbiting the pair of 'eclipsing binary stars' at the centre of the star system, which are together called 'KIC 4862625'. The larger star of the pair is about one and a half times the size of our Sun, and the smaller of the pair is less than half the size of the Sun. They orbit around each other with a period of about 20 days, and PH1 takes roughly 138 days to orbit around the both of them. In relation to our solar system, that would put it somewhere between the orbits of Mercury and Venus.

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Little else is known about PH1 yet, but in light of its discovery, astronomers and astrophysicists are going to need to review their notes on planet formation, and expand the list of star systems they are searching for candidates.