My Three Suns

Not just the title of an excellent Futurama episode, but now a real place.  A planet has been found orbiting in a triple star system, a surprising find that may be more common than once thought.

Artist’s impression of triple star system HD 131399 showing the new planet. Credit: ESO/L. Calçada

Astronomers from the University of Arizona used the European Southern Observatory (ESO)’s Very Large Telescope (VLT) in Chile to directly image the new planet as it orbits the brightest star in a triple system 320 light years away, in the constellation Centaurus. Orbits like this are thought to be extremely unstable due to the varying gravitational field in the system.

“HD 131399Ab is one of the few exoplanets that have been directly imaged, and it’s the first one in such an interesting dynamical configuration,” said Daniel Apai, from the University of Arizona, USA, and one of the co-authors of the new paper.

Aside from its unique orbit, the planet is interesting in its own right, being one of the youngest exoplanets ever imaged, a newborn at 16 million years old.  Direct imaging often finds huge and hot exoplanets, but this world is one of the smallest and coldest to ever be imaged directly, a testament to the level of technology in the instruments used.

Imagine living on this planet, if you could. “For about half of the planet’s orbit, which lasts 550 Earth-years, three stars are visible in the sky; the fainter two are always much closer together, and change in apparent separation from the brightest star throughout the year,” adds Kevin Wagner, the paper’s first author and discoverer of HD 131399Ab.

Rare planetary configurations like this are valuable to astronomers, since they offer clues about planetary formation.  The study of extreme system allow for the testing of planetary formation theories.  Often, if there are holes in the theories, the extreme cases will reveal them.  Let’s see astronomers explain this one!

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