Which is correct: "The facts are known by us" or "The facts are known to us"?

Which is correct?

The facts are known by us

or

The facts are known to us

I think by is correct but my friends persist that it's to.

Solution 1:

Both are grammatically correct. However known to is idiomatic and included in Oxford Dictionaries' examples:

1. Recognized, familiar, or within the scope of knowledge:
   plants little known to western science

known, ODO

Known by in a passive construction such as that, although not incorrect, is definitely awkward. The passive voice is used when the agent is immaterial and omissible: "The facts are known." If the facts are known by us, then the passive-voice construction is unnecessary: "We know the facts." Subverting the use of the passive voice by tacking "by us" on the end is what makes it awkward.

Known to is an idiomatic set phrase and not a passive construction.