Figure 1: Artist’s impression of a gas giant planet.
HD 131399Ab is a young, Jupiter-like planet in a triple star system located ~320 light years away. Its host star, identified as HD 131399A, is an A-type star with 1.82 times the mass of the Sun and has an effective temperature of 9300 K. The projected separation of HD 131399Ab from its host star is 82 AU and the planet’s orbital period is roughly 550 years. HD 131399Ab is estimated to have 4 ± 1 times the mass of Jupiter and its effective temperature is 850 ± 50, making it one of the coldest directly imaged planets. Nevertheless, HD 131399Ab is still in the process of cooling down as it radiates away heat that was acquired during its formation. The triple star system that HD 131399Ab resides in is relatively young, estimated to be only ~16 million years old.
The two other stars in the triple star system are identified as HD 131399B and HD 131399C. Both stars circle around one another and together are referred to as HD 131399BC. HD 131399B is a G-type star with 0.96 times the mass of the Sun and an effective temperature of 5700 K. HD 131399C is a K-type star with 0.6 times the mass of the Sun and an effective temperature of 4400 K. The separation between HD 131399BC and HD 131399A is just over ~3 times the projected separation between HD 131399A and HD 131399Ab. With such a dynamically extreme orbital configuration, the orbit of HD 131399Ab around its host star is the widest known for a planet that orbits within a triple star system.
Figure 2: The orbital paths of HD 131399Ab and its three suns.
Reference:
Wagner et al. (2016), "Direct Imaging Discovery of a Jovian Exoplanet Within a Triple Star System", arXiv:1607.02525 [astro-ph.EP]