Planetary physics is a very complex subject that encompasses a variety of disciplines, such as geology and meteorology. The eight planets can be though of as three types—terrestrial, gaseous, and ice—while the large number of remaining objects in the Solar System fall into groups such as the asteroid, the Kuiper Belt objects (which includes Pluto and other recently-discovered dwarf planets), comets, etc. One can easily find books that cover every aspect of a single planet, as well as books that cover groups of planets and other objects by their type..
Most information on a planet comes from interplanetary spacecraft that either flew by a planet or dropped into orbit around a planet. The amount of information a single spacecraft can gather with well-designed experiments rapidly dwarfs the information that can be gathered by ground-based telescopes. As a consequence, the best sources of information about a planet are the books and conference proceedings inspired by the data returned by a spacecraft, as well as the conference articles and press kits that describe the expectations of a spacecraft's voyage prior to launch. An example of this for Saturn is the Cassini-Huygens Saturn Arrival: Press Kit.
A review of the physics of gaseous giant planets is given in the review article of Hubbard, Burrows, and Lunine (2002). the book by Rogers (1995) covers the physics of Jupiter's structure, going from the interior of the planet to the magnetosphere.
A book covering the physics of planetary rings is that of Fridman and Gorkavyi (1999). This book is highly technical, as it develops the mathematical physics behind planetary rings; it is probably only useful to those with a solid grounding in classical physics.
The Kuiper Belt, which is the belt of Pluto-like bodies beyond the orbit of Neptune, is described by a good review article of Luu and Jewitt (2002). This article discusses the observations of the Kuiper Belt, including the distribution of masses and the characteristic orbits of the Kuiper Belt objects. The article also describes the current theories for the evolution of the belt, its role in the orbital changes of the outer planets, and the seeding of the Oort cloud with new comets.
Cassini-Huygens Saturn Arrival: Press Kit. Washington, D.C.: NASA, June 2004.
Fridman, A. M., and Gorkavyi, N. N. Physics of Planetary Rings: Celestial Mechanics of Continuous Media. Berlin: Springer-Verlag, 1999.
Hubbard, W. B., Burrows, A., and Lunine, J. I. “Theory of Giant Planets.” In Annual Reviews of Astronomy and Astrophysics, edited by Geoffrey Burbidge, Allan Sandage, and Frank H. Shu, vol. 40. Palo Alto, California: Annual Reviews, 2002.
Luu, Jane X., and Jewitt, David C. “Kuiper Belt Objects: Relics from the Accretion Disk of the Sun.” In Annual Reviews of Astronomy and Astrophysics, edited by Geoffrey Burbidge, Allan Sandage, and Frank H. Shu, vol. 40. Palo Alto, California: Annual Reviews, 2002.
Rogers, John H. The Giant Planet Jupiter. Cambridge, Great Britain: Cambridge U. Press, 1995.