Gongs belong to the oldest and most important musical instruments of south East Asia. Their origins may be traced back to the second millennium B.C., but it is assumed that the gong is much older. In Chinese history, gongs are mentioned around 500 A.D., attributed to a nation called HSI YU between Tibet and Burma during the reign of emperor Hsuan Wu.

Historic research provides us with four main centres - Burma, China, Annam, Java - at least 7 gong shapes and sound structures stem from these regions. Only few families knew the tradition of gong making as it was passed from generation to generation. The art of making gongs was veiled in a sense of magic. Gong makers then believed that a gong could only succeed with the help of higher powers and, that they were exposed to such forces more so than ordinary humans.
The gong was an important element in the lives of Far East people and it still is in some countries today. In Asian families, the gong was an attribute of wealth and served as a status symbol. In rites, the gong was used in evocation of ghosts and in the banning of demons. Touching a gong brought you fortune and strength. In the rituals of the Far East, the gong has retained its special significance to this day.
Frank Perry, a sound healer from England, gives this brief history of the gongs.
The gongs I perform with are made by  Paiste, the world's leading gong maker. Paiste created a special series of gongs called Planetary gongs. I have three of those instruments, the Sun, Chiron, and Neptune. Here is a description of the planet gongs from the paiste web site.

Paiste Planet Gongs resemble Symphonic Gongs in character, but feature a strong fundamental note tuned to represent a natural harmonic series based on the orbital properties of Sun, the Earth, the Moon and the other planets as calculated by Hans Cousto. Planet gongs resonate harmonically with the cycles of the cosmos, communicating to us what has been known since antiquity as the "music of the spheres". Mysterious in sound colour, Planet gongs convey an unusual atmosphere.