Caption: "Our results show that there are 4 common planetary system architectures that are the most common type of planetary system architectures. About 8 of 10 planetary systems around stars visible in the night sky have one of these 4 common planetary system architectures" and "What surprised the team was that the of the 4 common planetary system architectures---the one that also includes the Solar System---seems to be the rarest class." quoted from SciTechDaily: Astronomers Show There Are Four Classes of Planetary Systems, 2023 Feb28. See also Mishra et al. 2023, arXiv:2301.02374, A framework for the architecture of exoplanetary systems. I. Four classes of planetary system architecture.

Proposed Classification of Planetary System Architectures:

1. "similar planetary system or similar architecture: When the masses of all planets in a planetary system are similar to each other, the architecture is similar. This architecture type is the most common in the Milky Way: about 8 of 10 planetary systems are similar. A famous example of similar architecture is Trappist-1." (Somewhat edited from Wikipedia: Planetary System: Classification of Planetary System Architectures.)
2. "mixed planetary system or mixed architecture: When the masses of all planets in a planetary systemarchitecture is mixed. examples of mixed architecture are GJ-876 and Kepler-89. (Somewhat edited from Wikipedia: Planetary System: Classification of Planetary System Architectures.)
3. UNDER CONSTRUCTION Ordered: If the mass of the planets in a system tends to increase with increasing distance from the host star, the system has an Ordered architecture. The Solar System, with small rocky planets in the inner part and giant planets in the outer part is a type of Ordered system.

Credit/Permission: © NCCR PlanetS, Illustration: Tobias Stierli 2023 / No permission Image link: SciTechDaily: Astronomers Show There Are Four Classes of Planetary Systems, 2023 Feb28.
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