Astrophysics vs planetary science

Planetary science (or more rarely
Planetology) is the scientific study of planets (including :
Celestial bodies (such as :
Comets) and planetary systems (in particular those of the Solar System) and the processes of their formation.

The Department of Astrophysical and Planetary Sciences is one of the few programs that combines both astrophysics and planetary science
Providing a unified view of space sciences; the solar system and comparative planetology; stellar and galactic astronomy; and cosmology.

In some cases
As in the introduction of the introductory textbook The Physical Universe by Frank Shu
"astronomy" may be used to describe the qualitative study of the subject
Whereas "astrophysics" is used to describe the physics-oriented version of the subject.

Theoretical planetary astronomy is concerned with dynamics:
The application of the principles of celestial mechanics to the Solar System and extrasolar planetary systems.
Observing exoplanets and determining their physical properties
Exoplanetology
Is a major area of research besides Solar System studies.
Every planet has its own branch.

Researchers combine theoretical simulations with observations of newborn planetary systems to understand how the diverse worlds we see came into existence

That includes the distribution of atoms and molecules making planets, particularly those required for Earth-like life

Of course, the best understood planetary system is our own Solar System

This field encompasses research on the planets, comets, and other inhabitants of the Solar System, as well as studies of exoplanets and newborn planetary systems

Center for Astrophysics | Harvard & Smithsonian scientists engage in many types of planetary systems research: Finding and describing new exoplanets using TESS and other observatories

The Department of Astrophysical and Planetary Sciences is one of the few programs that combines both astrophysics and planetary science, providing a unified view of space sciences; the solar system and comparative planetology; stellar and galactic astronomy; and cosmology