Largest Solar System Yet Found Features Giant Planet 1 Trillion Kilometers From Mother Star

An artist’s impression of 2MASS J2126. 

Credit: University of Hertfordshire / Neil Cook.

Only a handful of extremely wide pairs of this kind have been found in recent years. The distance between the new pair is 6,900 Astronomical Units (AU) – 1,000,000,000,000 kilometres or 0.1 light years – nearly three times the previous widest pair, which is 2,500AU (370,000,000,000 km).

2MASS J2126−8140′s parent is a red dwarf star called TYC 9486-927-1. At that distance, it would appear as only a moderately bright star in the sky, and light would take about a month to reach the planet.

Dr Murphy is part of an international team of scientists that studied 2MASS J2126−8140, a gas giant planet around 12 to 15 times the mass of Jupiter, as part of a survey of several thousand young stars and brown dwarfs close to our solar system.

 

Credit: 2MASS/S. Murphy/ANU.

Once they realized 2MASS J2126−8140 and TYC 9486-927-1 were a similar distance from the Earth – about 100 light years – they compared the motion of the two through space and realised they were moving together.

“We can speculate they formed 10 million to 45 million years ago from a filament of gas that pushed them together in the same direction,” Dr Murphy said.

“They must not have lived their lives in a very dense environment. They are so tenuously bound together that any nearby star would have disrupted their orbit completely.”

In the last five years a number of free floating planetshave been found. These are gas giant worlds likeJupiter that lack the mass for the nuclear reactions that make stars shine, so cool and fade over time. Measuring the temperatures of these objects is relatively straightforward, but it depends on both mass and age. This means astronomers need to find out how old they are, before they can find out if they are lightweight enough to be planets or if they are heavier ‘failed stars’ known as brown dwarfs.

US-based researchers found 2MASS J2126 in an infrared sky survey, flagging it as a possible young and hence low mass object. In 2014 Canadian researchers identified 2MASS J2126 as a possible member of a 45 million year old group of stars and brown dwarfs known as the Tucana Horologium Association. This made it young and low enough in mass to be classified as a free-floating planet.

In the same region of the sky, TYC 9486-927-1 is a star that had been identified as being young, but not as a member of any known group of young stars. Until now no one had suggested that TYC 9486-927-1 and 2MASS J2126 were in some way linked.

Lead author Dr Niall Deacon of the University of Hertfordshire has spent the last few years searching for young stars with companions in wide orbits. As part of the work, his team looked through lists of known young stars, brown dwarfs and free-floating planets to see if any of them could be related. They found that TYC 9486-927-1 and 2MASS J2126 are moving through space together and are both about 104 light years from the Sun, implying that they are associated.

 

Based on this age the team was able to estimate the mass of 2MASS J2126, finding it to be between 11.6 to 15 times the mass of Jupiter. This placed it on the boundary between planets and brown dwarfs. It means that 2MASS J2126 has a similar mass, age and temperature to one of the first planets directly imaged around another star, beta Pictoris b.

“Compared to beta Pictoris b, 2MASS J2126 is more than 700 times further away from its host star,” Dr Simon Murphy of the Australian National University, also a study co-author, “but how such a wide planetary system forms and survives remains an open question.”

2MASS J2126 is around 7000 Earth-Sun distances or 1 trillion kilometres away from its parent star, giving it the widest orbit of any planet found around another star. At such an enormous distance it takes roughly 900,000 years to complete one orbit, meaning it has completed less than fifty orbits over its lifetime. There is little prospect of any life on an exotic world like this, but any inhabitants would see their ‘Sun’ as no more than a bright star, and might not even imagine they were connected to it at all.

Dr Phil Dooley