Scientists have discovered that a distant exoplanet has shown a rebellious personality, openly defying and even orbiting in the opposite direction of its host red dwarf star.
This latest finding was announced by an international research team led by the University of Geneva’s astronomy department. Astronomers used the NIRPS infrared high-precision spectrograph installed at the La Silla Observatory in Chile to successfully measure the abnormal orbit of an exoplanet named “GJ 3090 b,” which is located approximately 73 light-years away from Earth.
The research revealed that this planet not only has an extremely inclined orbit but also exhibits a phenomenon known as “retrograde motion,” meaning it rotates in the opposite direction to the rotation of its host star.
The study results were published on Tuesday (September 22nd) in the prestigious academic journal “Astronomy & Astrophysics” and were reported by media outlets such as the technology news website Space.com.
In a normal planetary formation model, both a star and its surrounding gas and dust disk (proto-planetary disk) collapse from the same cloud of gas, and their rotation directions should be the same, resulting in planets orbiting in the same direction roughly parallel to the star’s equator.
For example, in the case of our solar system, the angle (known as the Psi angle, Ψ) between the orbital plane of the eight major planets and the solar equatorial plane is only between 3 and 7 degrees (Earth’s being about 7 degrees). Pluto, which has been reclassified as a dwarf planet, has a significantly higher orbital inclination compared to other planets.
However, the research team found that the Psi angle of GJ 3090 b is remarkably high at 136 degrees. While a few extreme systems with Psi angles exceeding 70 degrees have been discovered in the universe, those systems typically have a massive companion star (such as a gas giant or brown dwarf) nearby exerting gravitational influence. In contrast, GJ 3090 b, first captured by NASA’s TESS space telescope in 2022, is a “lone ranger” without any large mass companion.
The parent star GJ 3090 is a lower temperature, smaller red dwarf star, while the planet GJ 3090 b has a radius 2.2 times that of Earth and a mass 4.5 times that of Earth, belonging to the most common type of “sub-Neptune” planets in the Milky Way galaxy.
Relying on the Swiss-manufactured NIRPS infrared spectrograph, astronomers were able to accurately measure the orbital angles of such a tiny planet and confirm the existence of two other planets within the system.
Regarding the phenomenon of this rebellious exoplanet orbiting “retrograde” without the gravitational interference of a companion star, co-author of the paper and University of Geneva researcher Vincent Bourrier proposed a new hypothesis: in the early stages of the system’s formation, the parent star may have accreted a secondary disk that was both offset and in reverse, and GJ 3090 b and the other planets in the system were subsequently born in this retrograde secondary disk.