Astronomers have made a groundbreaking discovery that challenges conventional understanding of planetary formation in binary star systems. A planet orbiting in a retrograde direction, opposite to its binary stars’ movement, has been confirmed in the nu Octantis system.
Located about 2.9 billion years old, the nu Octantis system features two stars: nu Oct A, a subgiant roughly 1.6 times the mass of the Sun, and nu Oct B, which is about half the Sun’s mass. These stars orbit each other once every 1,050 days.
The discovery was led by Professor Man Hoi Lee and his team from the University of Hong Kong, who used precise radial velocity data gathered using the European Southern Observatory’s HARPS spectrograph to confirm the planet’s unusual orbit.
Retrograde orbits are rare in planetary systems, and theoretically difficult to form or maintain, particularly in binary star systems where gravitational influence can make stable planetary orbits highly improbable. However, this discovery suggests that retrograde planets could be more common than previously thought, especially in systems with evolved stellar components like white dwarfs.
The team’s research adds to a growing body of evidence suggesting that retrograde planets could offer a new window into the formation and evolution of planetary systems. The nu Octantis planet’s unusual orbit presents an anomaly that has puzzled scientists for years, but further analysis revealed that the system is about 2.9 billion years old, with nu Oct B evolving into a white dwarf about 2 billion years ago.
This discovery introduces the possibility that the nu Octantis planet is a second-generation planet, either captured from a prograde orbit or formed from material expelled by nu Oct B. This insight opens up new avenues for studying the evolution of planets, especially those formed in unusual circumstances or captured from other orbits.
The study challenges traditional models of planetary formation, indicating that binary star systems may be capable of fostering unique planetary environments, offering insights into planetary migration, capture, and secondary planetary formation.
Source: https://dailygalaxy.com/2025/08/scientists-find-planet-orbiting-backwards