A team of astronomers led by the University of Arizona found a planet inside a triple-star system or a planet with three suns using the ESO’s Very Large Telescope (VLT).  They call this HD 131399Ab, a 16 million-year-old planet located 320 million light years away from us in the constellation of Centaurus.

HD 131399Ab is the first one of its kind found. Although scientists theorized that the orbit of a planet in a triple-star system is unstable due to changing gravitational attraction from the stars, the newly discovered one is actually secure, implying that more planets with three suns could probably exist in the universe.

As described in the journal published in July 7 in the journal Science, the planet experiences constant daylight or three sunrises and three sunsets every day. The researchers add that the seasons on HD 131399Ab lasts longer than human lifetimes.

This artist's impression of the triple-star system. Credit: ESO/L. Calçada

This artist’s impression of the triple-star system. Credit: ESO/L. Calçada

The age of HD 131399Ab, which weighs four Jupiters, makes it one of the youngest exoplanets scientists found so far. Its temperature is around 580 degrees Celsius, making it among the coldest exoplanets.

“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,” says the study’s first author and the planet discoverer Kevin Wagner, a PhD student at the University of Arizona.

According to the research team, HD 131399Ab travels around the brightest of the three suns (star A) in an orbit that measures two times bigger than Pluto or about 80 astronomical unit (au), or 80 times the distance between the Earth and the sun. As of now, they cannot explain how the planet got this large orbit.

However, according to the study co-author Daniel Apai, from the University of Arizona, USA, if HD 131399Ab was further away from its star, then it could have floated away of the system. Even doing some minor changes to its orbit can make it unstable rapidly.

The study on this triple-star system is still incomplete. But the scientists believe that star A’s mass is 80 percent more than the sun.

They also speculate that the two less massive stars, star B and star C, spin around each other like a spinning dumbbell. The distance between star B and C is equivalent to 10 au or approximately the same distance between the sun and Saturn.