There are also rubber stamp cachets, label cachets, etc. All covers are unaddressed unless otherwise noted. They all are in two colors and depict the Mariner spacecraft and give details of the mission.
All commemorative covers are for launches unless otherwise noted.
Word Rubber stamp cachet plus photo label cachet shows flyby of Mars. One-line word rubber stamp cachet plus pictorial rubber stamp cachet of the Mariner spacecraft. Three-line purple word rubber stamp cachet plus pictorial blue rubber stamp cachet of Mariner spacecraft. Large Address label. The two closest planetary neighbors of Earth are Venus and Mars and these were focused on for observation in the early days on man's exploration of our solar system.