Sub-Neptune planets that move in sync with the rest of their planetary systems are less dense than those that don’t, according to planetary scientists. These planets, known as “sub-Neptunes,” are the most common type of planets in the Milky Way, despite not being present in our solar system. They are estimated to orbit around 30% to 50% of sun-like stars. However, measuring the densities of these sub-Neptunes has been challenging for scientists studying exoplanets.
Recent research from the University of Geneva (UNIGE) and the University of Bern (UNIBE) suggests that there are two distinct families of sub-Neptunes, categorized as “puffy” and “non-puffy.” Puffy sub-Neptunes are more likely to be in resonance with their planetary siblings, meaning they orbit in a synchronized manner. One such resonant planetary system, HD 110067, consists of six sub-Neptune worlds that orbit around each other in a precise cosmic waltz. This rhythmic dance has been ongoing for about 4 billion years, similar to the age of our solar system.
The team of researchers has proposed that the lightness of resonant sub-Neptunes may be linked to how they were formed. They suggest that planetary systems initially converge toward a resonant chain during their early formation, but only a small percentage of systems can maintain this rhythm. The breaking of the resonance chain can lead to catastrophic events, causing planets to collide and merge, resulting in denser conglomerate worlds.
To estimate the density of a planet, astronomers need to know its mass and radius. Different methods, such as Transit Timing Variation (TTV) and radial velocity, are used to obtain mass measurements of exoplanets. The TTV method tends to detect sub-Neptune planets with lower densities compared to the radial velocity technique. Further analysis showed that the densities of these planets were lower in resonant systems than in non-resonant systems, regardless of the method used to determine their mass.
With the discovery of two distinct families of sub-Neptunes and the correlation between puffy planets and resonant planetary systems, scientists are gaining a better understanding of the evolution of these common planets in our galaxy. This research may also provide insights into why our solar system lacks such a world. The team’s findings have been published in the journal Astronomy & Astrophysics.
Overall, this research sheds light on the complex dynamics of sub-Neptune planets and how their synchronization with other planets in their systems can impact their density and evolution. By studying these planetary systems, scientists can uncover more about the formation and development of different types of planets in the universe.
