Caltech planetary sciences offers an undergraduate option and a PhD program for graduate students. We do not offer a separate Masters program, though some students obtain this degree in Planetary Sciences or another GPS option as part of their pursuit of a PhD.
At the undergraduate level, the option offers the opportunity to pursue a Caltech BSc with a concentration of courses in the planetary sciences option and in related areas. For some students, a physics, astronomy, geology or chemistry emphasis is as good or better than a planetary science major, and it is possible to prepare well for graduate school without doing a planetary science major as an undergraduate. The Caltech PS concentration is flexible but provides a wide-ranging introduction to the field, and many students have the option of research during summers and occasionally during the academic year.
At the graduate level, Caltech is one of the pre-eminent groups in the world with a wide range of research opportunities and advanced course work. The opportunities extend beyond the planetary science group: It is possible to do planetary science at the PhD level without being in the planetary science option (e.g., in geology) and it possible to do planetary research with a non-planetary science faculty member or with a JPL scientist co-mentor. A highlight of the Caltech Ph.D. is that during there first year, all students work with two different faculty (both need not be planetary sciences faculty) on two distinct projects. Some continue to span multiple research areas for their Ph.D. Admission is based more on general excellence than on a close match to a particular research area, and it is possible to be admitted without a precise idea of which subfield is preferred. All admissions are done through Caltech's graduate office and their web page provides information on the admission process.
The online catalog also provides information on the requirements for the undergraduate option and the graduate option. For the graduate program, a document outlining expectations for a typical Ph.D. trajectory is here. For complete information you need to consult the online catalog. (Planetary Science Option Requirements and Planetary Science Graduate Program). Information on Caltech courses in the GPS option is here.