Astronomers have identified GJ 3090 b, a Neptune-sized planet, orbiting its host star in the opposite direction to the star’s rotation, a phenomenon not previously confirmed around an M dwarf star. Researchers at Queen Mary University of London played a crucial role in this discovery, which may provide insights into the formation and evolution of planetary systems.
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Typically, planets formed from the same rotating disk of gas and dust as their star orbit in the same direction. However, GJ 3090 b challenges this expectation, raising questions about its unusual orbital path. The planet orbits an M dwarf star, which is one of the most common types of stars in the galaxy.
Using high-resolution data from the NIRPS near-infrared spectrograph, the research team measured the planet's orbital orientation, determining an obliquity of approximately 136 degrees, indicating it orbits backwards. Dr. Andrew Winter, one of the study's lead authors, emphasized the significance of the planet's retrograde orbit and the questions it poses about its formation.
Published in Astronomy & Astrophysics Letters, the researchers explored the possibility that GJ 3090 b might have inherited its retrograde orbit from earlier material the star acquired in its formative years. Assistant Professor Vincent Bourrier of the University of Geneva noted that this scenario suggests a planetary system could be reshaped by a differently oriented disk, influencing the arrangement of planets.
Alternatively, gravitational interactions with a massive outer planet or companion star can also alter a planet's orbit. The team searched for such companions within the GJ 3090 system but found no evidence of any, which indicates that the system's architecture may have formed through unknown mechanisms.
GJ 3090 b is noted as the smallest planet around an M dwarf for which a three-dimensional orbital obliquity has been measured. This research illustrates the potential of near-infrared observations to unravel complex planetary systems. Further investigations will be necessary to determine if similar extreme orbital arrangements exist in other systems.