Discovery shows 'lonely planet' has distant parent
A "lonely planet" that was thought to be floating on its own in space has a parent, scientists have discovered - but they are hardly close.
Astronomers were astonished to find that the planet, known as 2MASS J2126, orbits its star at the enormous distance of around one trillion kilometres, or 6.2 billion miles.
The pair are 7,000 times further apart than the Earth and the sun.
Dr Niall Deacon, from the University of Hertfordshire - who led the international team, said: "This is the widest planet system found so far and both the members of it have been known for eight years, but nobody had made the link between the objects before.
"The planet is not quite as lonely as we first thought, but it's certainly in a very long distance relationship."
Several free-floating planets - Jupiter-like gas giant worlds with insufficient mass to trigger the nuclear reactions that make stars shine - have been spotted in the last five years.
2MASS J2126 was initially identified as a "possible low mass object" by US-based astronomers in an infra-red sky survey. Then in 2014, Canadian scientists confirmed that it was young and light enough to be classified as a free planet.
Dr Deacon's team noticed that 2MASS J2126 was moving through the same region of space as a young star, TYC 9486-927-1, and the two seemed to be associated. Both are about 104 light years from the sun.
A more detailed look showed that the two objects were not members of any known group of young stars.
The astronomers were able to estimate the mass of 2MASS J2126 at between 11.6 and 15 times that of Jupiter, placing it on the boundary between planets and failed stars known as brown dwarfs.
Its orbit is so vast that it takes roughly 900,000 years to complete one journey round its star. In the whole of the planet's life, less than 50 of its years are thought to have passed.
There is little prospect of anything living on 2MASS J2126, but if the planet had inhabitants they would see their "sun" as little more than a bright star.
Dr Simon Murphy, another member of the team from the Australian National University, said: "How such a wide planetary system forms and survives remains an open question."
The research is published in the journal Monthly Notices of the Royal Astronomical Society.