Tatooine +1: Newly-discovered planet with 3 suns facing potential annihilation

Artist’s impression of planet in the HD 131399 system © ESO/L. Calçada/M. Kornmesser
Meet HD 131399ab - the planet with three suns that experiences triple sunsets and could be ejected from its current system at any time.

The mysterious planet is four times heavier than Jupiter with an orbit twice as wide as Pluto’s.

The University of Arizona, which led the astronomy team, explained. "Imagine this: a planet where you'd either experience constant daylight or enjoy triple sunrises and sunsets each day, depending on the seasons, which happen to last longer than human lifetimes.”

Artist’s impression of planet in the HD 131399 system © ESO/L. Calçada/M. Kornmesser

Some 340 light years away, HD 131399ab is in the Centarus constellation, and has been around for at least 16 million years.

With a similar atmosphere to Jupiter and Saturn, comprising largely hydrogen and helium, its temperature is about 580 degrees Celsius (+1076 Fahrenheit)

The planet orbits the biggest star, HD 131399A, which is blue-white and almost twice the size of our sun. A single orbit takes 550 years to complete.

The other two stars  - HD 131399B, and HD 131399C -  also orbit the biggest star while closely orbiting each other.

“For much of the planet’s year the stars appear close together, giving it a familiar night-side and day-side with a unique triple-sunset and sunrise each day,” said Kevin Wagner, the University of Arizona PhD candidate who discovered the system.

“As the planet orbits and the stars grow further apart each day, they reach a point where the setting of one coincides with the rising of the other — at which point the planet is in near-constant daytime for about one-quarter of its orbit, or roughly 140 Earth-years.”

While HD 131399ab isn’t the only planet to orbit multiple stars, what makes this discovery so special is the fact it may not be around for long.

Artist’s impression of planet in the HD 131399 system © ESO/L. Calçada/M. Kornmesser

Astronomers say it is possible that the planet will be ejected from its system. Planets with multiple suns (multistar systems) survive as long as the orbital dynamics remain balanced. These systems carry a risk of annihilation as all the elements can crash into each other.

HD 131399ab orbits 7.6 billion miles (12.2 billion km) from its sun, and risks getting too close to the two stars that share its sun.

The planet was discovered using the European Southern Observatory’s Very Large Telescope and SPHERE, the Spectro-Polarimetric High-contrast Exoplanet Research Instrument, in Chile.