Astronomers Discover Exoplanet with Widest Orbit Ever Seen

The objects are both 104 light years away from the earth.

One year on this planet is equivalent to 900,000 Earth years, i.e. every time 2MASS J2126 completes one orbit around its star, Earth has done 900,000 orbits around the Sun.

The findings have been accepted for publication in the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint).

In the last five years a number of free-floating planets have been found. These are gas giant worlds like Jupiter that lack the mass for the nuclear reactions that make stars shine, so cool and fade over time. But a team of astronomers in the UK, USA and Australia found the planet’s home star.

U.S.-based astronomers spotted 2MASS J2126 during an infrared sky survey and noted that it appeared to be a young, low-mass object. Researchers found that TYC 9486-927-1 had stronger signatures than a group of young star but weaker signatures than a group of 10 million old stars, so it falls somewhere between the two categories.

How such a wide orbit could have been established remains a mystery. Previous studies had estimated 2MASS J2126’s temperature to be about 2,730 degrees Fahrenheit (1,500 degrees Celsius).

As part of the work, Dr. Deacon and colleagues sifted through lists of brown dwarfs, free-floating planets, and young stars to see whether any of them might be related. Also, they are moving through space together, i.e., in the same direction.

False colour infrared image of 2MASS J2126 and TYC 9486-927-1. This shows they are associated; and the scientists have been successful in establishing that this association can be extended to a planet-star relationship. The fantastic object, called 2MASS J2126, is about seven thousand times further from its star than the Earth is from the Sun. Image credit: “2MASS/S. Murphy/ANU”.

Dr. Niall Deacon of the University of Hertfordshire and his team have now, after years of extensive search and research, provided a link between the two.

The team then looked at the spectrum – the dispersed light – of the star to measure the strength of a feature caused by the element lithium. Since lithium burns up over a star’s lifetime, the amount present is an indicator of age.

Knowledge of the planet’s age allowed the researchers to calculate a mass for the planet: about 12 to 15 times that of Jupiter. Right at the edge separating planets and brown dwarfs.

Instead, scientists say that 2MASS J2126 may be the widest orbit exoplanet ever discovered.

“We were very surprised to find such a low-mass object so far from its parent star”, said Dr Simon Murphy of the Australian National University Research School of Astronomy and Astrophysics.

Scientists were studying a planet that they thought was just aimlessly wandering through space, but they discovered it is actually orbiting a host star roughly one trillion kilometres away from it.

The gap between the planet and star is so big that one full orbit takes the equivalent of nearly a million years.