massive they are. As the star loses mass, planets that are not engulfed move further out from the star. If an evolved star is in a binary or multiple system, then the mass it loses can transfer to another star, forming new protoplanetary disks and second- and third-generation planets which may differ in composition from the original planets, which may also be affected by the mass transfer. System architectures The Solar System consists of an inner region of small rocky planets and outer region of large gas giants. However, other planetary systems can have quite different architectures. Studies suggest that architectures of planetary systems are dependent on the conditions of their initial formation. Many systems with a hot Jupiter gas giant very close to the star have been found. Theories, such as planetary migration or scattering, have been proposed for the formation of large planets close to their parent stars. At present, few systems have been found to be analogous to the Solar System with terrestrial planets close to the parent star. More commonly, systems consisting of multiple Super-Earths have been detected. Classification of Planetary System Architectures Research has shown that there are four classes of planetary system architecture. The four classes of planetary system archtecture are defined based on how the mass of the planets is distributed around the host star. The different types of planetary systems, when classified using planetary masses, are: Similar: When the masses of all planets in a system are similar to each other, the system's architecture is Similar. This architecture type is the most common in our galaxy. Famous example of this type of planetary system is Trappist-1. The planets in these systems are said to be like 'peas in a pod'. Mixed: When the masses of planets in a system show large increasing or decreasing variations, the system's architecture is Mixed. Example of such systems are: GJ-876 or the Kepler-89 system. Anti-Ordered: If the massive planets of a system are close to the star and smaller planets are further away from the star, this architecture is Anti-Ordered. There are currently no-known examples of this system. 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