unknown vs unidentified

unknown is a noun but unidentified is not a noun.

Word	Noun	Adjective	Verb	Adverb
unknown	Yes	Yes	No	No
unidentified	No	Yes	No	No

As adjectives, unknown and unidentified are synonyms defined as:

Other synonyms of unknown include nameless, unnamed.

unknown (noun)	unidentified (noun)
a variable whose values are solutions of an equation
an unknown and unexplored region
anyone who does not belong in the environment in which they are found

unknown (adjective)	unidentified (adjective)
not known	being or having an unknown or unnamed source
being or having an unknown or unnamed source	not yet identified
not famous or acclaimed
not known before
not known to exist