Currently, Pluto is the planet we think of being on the edge of our planetary system. But the new body would be 30,000 times more distant from the Sun than the Earth - putting it a significant distance on the way to the nearest star.
What is more, it seems that the new planet cannot be a true member of
our Sun's family of planets. It may be a planet that was born elsewhere,
and roamed throughout the galaxy only to be captured on the outskirts of
our own Solar System.
years, he has been studying the peculiar motions of so-called
They spend millions of years in the Oort cloud, until they are deflected into an orbit that takes them into the inner Solar System where we can see them.
By analyzing the orbits of 13 of these comets, Dr Murray has detected the tell-tale signs of a single massive object that deflected all of them into their current orbits.
In a research paper to be published next week in the Monthly Notices of the Royal Astronomical Society, he suggests that the so-far unseen planet is several times bigger than the largest known planet in our Solar System, Jupiter.
Being so far from the Sun - three thousand billion miles - it would take almost six million years to orbit it.
But the planet orbits our Sun in the "wrong" direction, counter to the
direction taken by all the other known planets.
It is this which has led to the remarkable suggestion that it did not
form in this region of space along with the Sun's other planets, and
could be a planet that "escaped" from another star.
His research is to be published in Icarus, the journal of Solar System studies.