"Astronomers have confirmed the existence of a rare, retrograde-orbiting planet in a tight binary star system.
Most stars throughout the Universe are part of binary or multiple star systems. In these systems, a nearby companion star can make it difficult for planets to form and remain in stable orbits around just one of the stars.They identified a planet orbiting in the opposite direction of its binary stars’ movement, known as a retrograde orbit, within the nu Octantis binary system.
The nu Octantis system contains two closely bound stars. The primary star, nu Oct A, is a subgiant with approximately 1.6 times the mass of the Sun. Its companion, nu Oct B, has roughly half the Sun’s mass. Together, the two stars complete an orbit around each other every 1,050 days.
This signal was consistent with the presence of a Jovian planet of about twice the mass of Jupiter orbiting around the primary star, nu Oct A, with a period of about 400 days.
However, the existence of this planet has been controversial because its orbit would be so wide that it could only remain stable if it were retrograde and moved in the opposite direction to the orbit of the binary. There were no observational precedents for such a planet and strong theoretical grounds against its formation."
SciTechDaily