A team of astronomers, led by the University of Arizona, announced in July 2016 that they had used the direct imaging technique to discover planet HD 131399Ab. This planet is about 340 light years from Earth and roughly 16 million years old. It has the widest orbit yet discovered for a planet in a multi-star system – one revolution lasts approximately 550 Earth-years.

HD 131399Ab is relatively small and cold for an exoplanet – it’s only four times the size of Jupiter, with a surface temperature of 580° Celsius. It has three suns, one large and bright, while the other two, which orbit around each other, are smaller and fainter. For around half the planet’s yearly cycle (about 275 Earth-years), the three suns are close together in the sky. They rise and set together, giving the planet regular days and nights. However, for one quarter of HD 131399Ab’s year its suns no longer move together. One will rise when the other two set, so that the planet is constantly lit, experiencing one long day that lasts around 140 Earth-years.

It might seem like something out of Star Wars, but such planets are actually as commonly found in the Universe as single-sun planets like our Earth. Scientists learn a great deal from studying planetary systems such as HD 131399Ab, since they are so different from our own solar system.

Read more about them in the NASA article “Newly-Discovered Planet Has 3 Suns” edited by Rob Garner.