planetary system; star system
Refers to a system of planets orbiting a star, or more broadly a star system. In astronomy, 惑星系 often specifically means a planetary system, while 恒星系 is used for a star system.
See also: 恒星系
The solar system is one planetary system.
Astronomers discovered a new planetary system.
太陽系 is the proper name for our solar system, whereas 惑星系 is a general term for any planetary system.
protoplanetary disk
Compound of 惑星 (planet) + 系 (system). A straightforward modern technical term.