A difference is made between planets in astrology and planets in astronomy. The planets in astronomy are gaseous or rocky bodies that revolve around the sun (or other stars, as in the case of exo-solar planets). The planets in astrology are archetypal attributes, which seem to be a juxtaposition of Jungian archetypes, subtle physical/etheric spheres, and astral thoughtforms. Just why these non-physical qualities should be associated with the astronomical bodies is not clear. There are a number of possible explanations, which hopefully I'll write up when I get around to it
In the meantime, the astrological planets can be listed as follows (to save tedious rewriting, the following accounts are taken from the Wikipedia page "Planets in astrology"
It is possible to interpret the planets as psycho-socio-spiritual archetypes of personal and transpersonal consciousness; in this way astrology can be understood as a profound system of holistic analysis and typology. Matched with similar subsystems, one glimpses a web of symbolic and esoteric interrelationships. This should be one of the subjects considered by any truly integral and universal system of understanding.