Gliese 3090 b is a sub-Neptune planet orbiting an inner position within a multi-planet system around a Red dwarf star. Recent observations reveal that this planet moves in a retrograde orbit, meaning it travels in the opposite direction to the rotation of its host star. This configuration is highly unusual for small planets orbiting Red dwarf stars, providing new information about how planetary systems develop and migrate over time.
To determine the orientation of the orbit, the Rossiter-McLaughlin effect was measured. This phenomenon occurs when a planet transits, or passes in front of, its star, causing a characteristic distortion in the light spectrum of the star that reveals the alignment between the star's spin axis and the planetary orbital plane. By observing six transits with high-resolution spectrographs, the planet was found to have an orbital obliquity of approximately 136 degrees.
The absence of massive outer planetary or stellar companions suggests that the misalignment is not caused by gravitational tugs from other large bodies. Instead, the findings point toward a primordial misalignment of the protoplanetary disk, likely followed by disk-driven migration. This indicates that the architecture of the system was determined early in its formation, potentially during a phase of late secondary disk accretion.
Key findings
- Gliese 3090 b is confirmed as the first retrograde planet discovered around a Red dwarf.
- The planet exhibits an orbital obliquity of 136 degrees.
- The system is the first highly misaligned multi-planet system found without massive external companions.
- Data suggests the misalignment originated from the early protoplanetary disk rather than later gravitational interactions.
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22. 9. 2026
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