This is the 12703rd most frequent Russian word.
космоса
The Russian word "космоса" means "of space" or "of the cosmos."
Here, 'космоса' is used in the singular genitive case, denoting possession or association with 'space' as a concept of the universe.
Красота космоса поражает воображение.
The beauty of space amazes the imagination.
In this sentence, 'космоса' is also in the genitive case, illustrating the relationship between 'mysteries' and 'space' as the realm these mysteries belong to.
Мы ещё мало знаем о тайнах космоса.
We still know little about the mysteries of space.
Here, 'космоса' is again in the genitive case, signifying the action of exploring pertaining to 'space' or the cosmos.