The Largest Solar System Ever Discovered Has Only One Planet

January 28, 2016 | Joanne Kennell

Artist's impression of Sedna, a red planet
Photo credit: NASA/JPL-Caltech/R. Hurt

This ‘lonely planet’ is in a very long distance relationship with its star.

A team of astronomers from the University of Hertfordshire, USA and Australia have found the largest known solar system — linking a previously thought free-floating planet in an orbit roughly 1 trillion kilometers from its star.

Free-floating planets are gas giants like Jupiter that do not orbit a star, but rather float aimlessly within galaxies.  They were either forced out of their solar system, or they formed extremely early on in the universe and their star has died.

The planet is 12 to 15 times the mass of Jupiter and is located 100 light-years away from Earth.  It is known as 2MASS-J2126-8140, and its star is called TYC 9486-927-1.  They were both identified eight years ago, however, since they are so far apart no one considered that the two might be related.  

“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,” said Dr. Niall Deacon of the University of Hertfordshire in the UK.  “The planet is not quite as lonely as we first thought, but it's certainly in a very long distance relationship.”

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2MASS’s orbit is about 7,000 times the distance from Earth to the sun, or about 140 times the distance between Pluto and the sun — making it the widest orbit of any planet around a star.  This enormous distance, which equates to 6,900 Astronomical Units (AU), means it takes the planet roughly 900,000 years to complete a single orbit.

The astronomers estimated the star’s age by examining the dispersed light of the star to measure how much lithium is left.  Lithium is destroyed during a star’s life, so the more lithium it has, the younger it is.  Using this method, they estimate that TYC 9486-927-1 is between 10 and 45 million years old — meaning that 2MASS has completed less than 50 orbits around the star.

You may be wondering if this planet could harbour life?  Well, it is very unlikely.  Not only because it is a gas giant, but also the planet is just too far from its sun.  According to the researchers, TYC 9486-927-1 would look like any of the other stars in the sky to inhabitants, if there were any.

“We were very surprised to find such a low-mass object so far from its parent star,” said Dr. Simon Murphy from the Australian National University (ANU) in a pressure release.  “There is no way it formed in the same way as our solar system did, from a large disc of dust and gas.”

Researchers discovered the planet and star were linked by comparing the motion of the two through space.  It turned out that they were moving together — it was a secret relationship!

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

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