"Free-Floating" Planet Turns Out to Have Million-Year Orbit

They're just really into long-distance.

University of Hertfordshire / Neil Cook

A lot of planets have homes — warm, loving stars that nurture and care for them and make sure they have everything they need. But sometimes, a planet finds itself homeless, moving around the universe aimlessness and carelessly. These free floaters just haven’t found a place to call home.

That was thought to be the case with 2MASS J2126, a gaseous nomad planet about 104 light-years from our own sun. While not common, free floating planets do exist. Astronomers, equipped with better instruments and more experience in how to find and identify strange objects in the universe, are in a better position these days to distinguish whether these lonesome celestial bodies are really planets, or just failed “brown dwarf” stars that couldn’t ignite.

In the same neighborhood, there was TYC 9486-927-1 — a young star thought to be on its own as well. No one really made any connections between 2MASS J2126 and TYC 9486-927-1. Why would they? The two are more than 6 billion miles from one another. That’s 7,000 times the distance between Earth and the sun. If the two were indeed pursuing an orbital relationship, it would take 2MASS J2126 nearly a million years to complete a single orbit around TYC 9486-927-1.

Well when it comes to space, time is relative. It turns out 2MASS J2126 has indeed found its host star in TYC 9486-927-1. It’s also the widest planetary system ever found, according to researchers at the University of Hertfordshire, who detail their findings in a new paper published today in Monthly Notices of the Royal Astronomical Society.

An artist’s impression of 2MASS J2126.

University of Hertfordshire / Neil Cook

“Nobody had made the link between the objects before,” said lead author Niall Deacon in a press release. “The planet is not quite as lonely as we first thought, but it’s certainly in a very long-distance relationship.”

The astronomers determined the link by measuring the orbital strength of the two lovebirds through the element lithium, which is very abundant in young stars and much rarer in older ones. The host star TYC 9486-927-1 looks to contain an amount of lithium characteristic of stars between 10 million and 45 million years old.

Knowing the age of the star allowed astronomers to determine the mass of 2MASS J2126 — which is estimated to be somewhere between 11.6 and 15 times the mass of Jupiter. It’s a hefty planet, but still too small to be a star. And it’s moving together with TYC 9486-927-1.

False color infrared image; the arrows show the projected movement of the star and planet on the sky over 1,000 years. The scale indicates a distance of 0.1 light-year. Light from the star takes about a month to travel to the planet.

2MASS/S. Murphy/ANU

A lot of questions remain about how such a star system forms and survives. This kind of orbit is basically stretched out to its limit. The sheer distance also means the likelihood that 2MASS J2126 could be habitable is close to nil. (Sorry.)

In any case, further study of this planet and star certainly makes it clear that we should take a closer look at other planets we’re calling free floaters — and how easy it might be for one of those little buggers to find a star system they can call home.