discover vs happen upon

discover and happen upon both are verbs.

Word	Noun	Adjective	Verb	Adverb
discover	No	No	Yes	No
happen upon	No	No	Yes	No

As verbs, discover and happen upon are synonyms defined as:

Other synonyms of discover include attain, chance on, chance upon, come across, come upon, fall upon, light upon, strike.

discover (verb)	happen upon (verb)
get to know or become aware of, usually accidentally	find unexpectedly
identify as in botany or biology, for example
make known to the public information that was previously known only to a few people or that was meant to be kept a secret
make a discovery, make a new finding
see for the first time; make a discovery
discover or determine the existence, presence, or fact of by perception with the eyes
find unexpectedly