Mysterious Object Turns Out To Be Two Escaping Planets

Artist's impression of the two binaries. Gemini Observatory/Jon Lomberg Illustration

Move over, Thelma and Louise! Make way, Bonnie and Clyde! There's a new couple of runaway rogues in town. Astronomers have discovered that a rogue planet, part of the TW Hydrae group of stars, is actually two planets orbiting each other.

The objects are known as 2MASS J11193254-1137466AB and they are about 3.7 times the mass of Jupiter each. It's difficult to put them in a box. They are too small to be a conventional brown dwarf and they are not exactly planets, although they have the right mass. That's why they are also called rogue planets – they are planetary mass objects without a star. This system is the lowest-mass, free-floating binary ever observed.

The objects were first discovered last year and are believed to be associated with the TW Hydrae group. In a paper published in the Astrophysical Journal Letters, the researchers provide an 80 percent chance that the rogue planets formed with the rest of the TW Hydrae association.

We are better at working out the properties of normal stars than unusual and extreme objects like the binary planet. We know that TW Hydrae formed about 10 million years ago and that the latest estimate for its distance is about 160 light-years from Earth.

That data also applies to the rogue planets, but based on the distance and apparent separation, astronomers have worked out that they are about 583 million kilometers (362 million miles) from each other. That’s almost four times the distance between the Sun and the Earth.

These two objects have been described as lying on a “nexus of astronomical” interest, being on a cross-category of space objects. They are likely made of the same stuff of brown dwarfs and yet are so small that their properties are closer to exoplanets. Studying them might actually give us more insight into how gas giant planets form and behave. It’s often difficult to study them because of the bright light of their host star, which is not an issue for our pair of rogue objects.

2MASS J11193254-1137466AB will certainly receive a lot more attention now that its binary status has been detected. There’s lot that we can learn from these two runaway objects.


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