Somewhere out in the universe is an exoplanet with not one, not two, but three suns. A team led by astronomers from the University of Arizona used the European Southern Observatory (ESO)’s Very Large Telescope to find HD 131399Ab, an exoplanet in what’s called a triple-star system. The cool space discovery could mean there are more planets in multi-star systems than we thought.
HD 131399Ab is not the first planet discovered with three suns, but it is one that is more likely to remain in its orbit. Normally when astronomers find planets with three suns, the planet’s orbit is unstable and it’s “quickly ejected” from the triple-star system. HD 131399Ab is different: it’s the “first planet ever found in a wide orbit inside a triple-star system.” The astronomers say this orbit “can be stable” but they need to do more research to determine if the orbit will continue to be stable long-term.
There are some interesting weather patterns on HD 131399Ab too: it either exists in a state of constant daylight or has triple sunsets and sunrises each day, depending on the season. But if we could stand on the planet, we’d only ever experience one or the other because HD 131399Ab’s seasons are longer than human lifetimes. HD 131399Ab is also one of the youngest exoplanets we’ve ever found at just around 16 million years old, compared to Earth’s estimated 4.5 billion years. It’s around 320 light-years away from us.
The astronomers published a paper detailing the discovery recently in Science. Along with astronomers from the European Southern Observatory and the University of Arizona, the team included researchers from the Space Telescope Science Institute in Maryland and the Institut de Planétologie et d’Astrophysique de Grenoble in France.
University of Arizona PhD student Kevin Wagner, who is the lead author on the paper, said in an ESO press release, “It is not clear how this planet ended up on its wide orbit in this extreme system, and we can’t say yet what this means for our broader understanding of the types of planetary systems, but it shows that there is more variety out there than many would have deemed possible. What we do know is that planets in multi-star systems…are potentially just as numerous as planets in single-star systems.”