A ‘hot Jupiter’ has been discovered within a three-star system; one of only four such systems found to date.


KELT-4Ab is described as a ‘hot Jupiter’ because it is a gas giant, like Jupiter in our own Solar System, but orbits extremely close to its host star, making it scorching hot.

The planet is about 685 lightyears from Earth and was discovered using the Kilodegree Extremely Little Telescope (KELT).

Justin R. Crepp, who was part of the team at the University of Notre Dame that made the discovery, was able to capture crisp photos revealing the true nature of the triple-star system.

The KELT telescope monitors bright stars in the search for planets orbiting extremely close by.

Star KELT-A was noticed to be dimming every few days, which led scientists to believe this was the sign of an orbiting planet.

Crepp then used the Keck Telescope to capture photos and found two additional stars.

“I found that there was a dot nearby, which we believed to be a star, making this a binary system,” Crepp says.

“And then upon further review, I found that it was two dots. We wouldn’t have realized that without these photos.”

KELT-4Ab is about one and a half times the size of Jupiter and orbits the system’s main star every three days.

The other two stars orbit each other every 30 years.

The study of these hot Jupiters is important because astronomers are still not sure as to how they get so close to their host stars.

“We still think they formed far from their star, but then somehow migrated close to their stars. We also don’t know how they stop migrating,” Crepp says.

“It is possible that companion stars drive the dynamics of planets such as to move the planets closer to the star.


This discovery has implications for our understanding of planet formation and evolution.”


Iain Todd, BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Content Editor. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.