Sound cannot travel in space because there is no matter to carry the vibrations. Molecules float back into the nasal cavity behind the bridge of the nose where they are detected by receptor cells. Five million of these cells fire impulses to the brain's olfactory bulb or smell center. Such cells are unique to the nose. Smell is stored almost exclusively in the long-term memory.
Smells stimulate learning and information.
Edwin T. Morris noted that a list of words was recalled much more easily and retained better when olfactory information was given along with a word list. Only substances volatile enough to spray microscopic particles into the air have a smell. When you smell chocolate chip cookies, you are actually smelling molecules of the cookie that have evaporated. Each person has an odor as individual as a fingerprint. In the absence of gravity, molecules will not float away easily, so the sense of smell is less effective.