The Planet With Three Suns Was Just a Ghost

One of the weirdest planets ever spotted by astronomers now appears to have been a false positive.

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Eric Mack
2 min read

This artist's impression shows a view of the HD 131399 system from an exoplanet that was once thought to exist, but the discovery has since been retracted.

ESO/L. Calçada

Perspective is important, even when it comes to astronomy. Just like those cheesy Instagram shots of tourists appearing to hold up famous landmarks by their fingers, sometimes an entire planet can be just an optical illusion. 

That's apparently what happened in the case of HD 131399Ab, a Jupiter-sized exoplanet that it now seems never existed. 

More recent observations have revealed that what looked like a planet was really an object in the background -- probably a star that's light-years away -- and the discovery of HD 131399Ab was retracted Thursday by the research team that claimed it and by the journal Science that published it. 

"It was quite a shock," lead author Kevin Wagner at the University of Arizona told me of learning that the planet was a phantom. "A number of unlikely parameters about the background object lined up to make it look extremely planet-like. Ultimately, more time and observations showed that it is not associated with the [star] system."

It's a shame, too, that this planet has to be scrubbed from the annals of astronomy because it would have been one of the most unusual and intriguing exoplanets yet discovered. The discovery was first announced in 2016, when it caught my attention as what seemed at the time to be the first known planet to orbit three suns.

You may recall that Luke Skywalker's fictional home planet of Tatooine had two suns, so HD 131399Ab would literally have been stranger than fiction. 

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When more recent observations suggested Wagner and colleagues were really seeing something in the distant background, they had another look for themselves over a longer time period to confirm that the planet was never really there. 

Wagner said it's a useful lesson that will ultimately improve astronomy and the search for exoplanets. 

"The background is not stationary, and sometimes a very fast moving star can have its motion aligned such that it passes our usual tests for common proper motion," he said. "This possibility is already starting to be accounted for in more recent studies, which is a positive outcome in my opinion."

So for now, the idea of a world 300 light years away with plentiful sunrises, sunsets and seasons that can last for centuries will have to remain in the domain of science fiction.