The given size is the inner diameter in mm. If deriving size from an existing ring, bear in mind the ring's width and inflexibility. Convert using Ring Sizes
MOLA data forms the outer surface of the ring, modelling the topography of Mars between approximately 30 degrees north and south of the equator. Vertical scale greatly exaggerated for clarity.
The inside of the ring consists of debossed icons of the Mars Pathfinder rover (Sojourner), the Mars Exploration Rover (Spirit/Opportunity), the Mars Science Laboratory (Curiosity), and a truncated hexa-octahedral magnetite crystal of the sort found in ALH84001 and the magnetotactic bacteria strain MV-1 - currently the strongest evidence in support of the hypothesis that life originated on Mars.
The ring is printed in raw metal and will take a few weeks of wear to smooth out the roughness which otherwise preserves a high level of surface detail. Bronze will stain skin (temporarily) green - a reminder of our duty to spread (multicellular) life to other planets, or possibly to coat the inside surface with clear nail polish.
Other sizes available: