MYSTERIES OF THE UNIVERSE:IS THERE ANOTHER PLANET BEYOND NEPTUNE?

There are now five lines of evidence suggesting the existence of Planet Nine

- David Crookes

Pluto used to be thought of as the ninth planet in the Solar System, but in 2006 the International Astronomical Union created an official definition for planets and decided Pluto didn’t fit all of the conditions. The upshot was a reclassification of the body discovered by Clyde Tombaugh at Lowell Observatory in 1930, with Pluto being labelled a ‘dwarf planet’ instead. But that’s not to say a ninth planet doesn’t actually exist. In fact, as time goes on, there’s more and more evidence to suggest one is very much out there.

The search for a ninth planet has been ongoing for some time. American astronomer Percival Lowell spent the last decade of his life looking for a hypothetical planet beyond Neptune – the so-called Planet X. It was thought that another planet in the outer reaches of the Solar System would account for the apparent irregularities in the orbits of Uranus and Neptune, and when Pluto was discovered it seemed the search was over.

In 1978, however, Pluto was dismissed as the cosmic influencer because it was too small to have any gravitational influence. Then it was found that Uranus’ orbit only differed from predictions because the calculated mass of Neptune had been incorrect. For a while, the idea that there could be another planet in the Solar System was put on the back burner – that is until scientists searched for a potential explanation for why some of the dwarf planets and other tiny icy objects follow orbits that cluster together. Faced with that conundrum, another planet in the far reaches of the Solar System seemed entirely plausible.