Scientists have discovered a rare triple-star system with a gas giant planet similar in size to Jupiter.

Researchers at the Harvard-Smithsonian Centre for Astrophysics in US found that a binary system once thought to be a single star was actually a pair of stars orbiting one another, and are a part of the triple-star system.

Known planets with three stars appearing in their sky are rare - the new discovery is just the fourth and the closest one yet, allowing for a better look than has been possible, researchers said.

The main star is also brighter than the other stars that serve as suns for their planets, making it easier to study both the star and the planet.

In the new system KELT-4Ab, a gas giant planet, similar in size to Jupiter takes approximately three days to make its way around the star KELT-A, which serves as its sun.

The other two stars, named KELT-B and C, are much farther away and orbit one another over the course of approximately 30 years. It takes the pair approximately four thousand years to orbit KELT-A, 'Phys.org' reported.

The view from KELT-4Ab would likely be one where its sun, KELT-A, would appear roughly forty times as big as our sun does to us due to its close proximity, researchers said.

On the other hand, the two other orbiting stars would appear much dimmer due to their great distance, shining no brighter than our moon, they said.

Scientists have known of the existence of the KELT system for several years, but it was thought that the binary stars were actually just one star.

The triple-star system offers a unique opportunity for scientists trying to understand how it is that gas giants, such as KELT-4Ab, manage to orbit so close to their star.

The research was published in The Astronomical Journal.