The Biggest Solar System Ever Found Is Very, Very Big

Planet 2MASS J2126-8140 orbits a trillion kilometers out from its sun

2MASS J2126-8140

Artist’s depiction of the gas giant planet in orbit around the red dwarf star TYC 9486-927-1, faintly visible in the background.University of Hertfordshire/Neil James Cook

Scientists used to suspect a giant planet named "2MASS J2126-8140" was a rogue world, wandering the galaxy without a star to orbit. But it turns out the planet isn't homeless after all: its star is just very, very far away. Like, a trillion kilometers away (or about 621,000,000,000 miles).

To put that number into context, that's around 6,900 times the distance between the Sun and Earth. Its orbit is 140 times wider than Pluto's. At that distance, the dim red dwarf star would look like just another moderately bright star in the sky.

Astronomer Simon Murphy from the Australian National University and his colleagues uncovered the secret relationship between the planet and star after noticing that they were both located 100 light-years from Earth. Further analysis showed they were moving together as well.

The planet is believed to be a gas giant 12 to 15 times the size of Jupiter, and takes nearly a million Earth years to circle its star.

Scientists aren't sure how such a far-flung solar system could have formed. “There is no way it formed in the same way as our solar system did, from a large disc of dust and gas,” Murphy said in a press statement.

Instead, the team suspects the star-planet duo were born relatively recently (10 to 45 million years ago, compared to our solar system's birth 4.5 billion years ago), and that they formed from “a filament of gas that pushed them together in the same direction," says Murphy.

"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.”