interplanetary space vs region

interplanetary space and region both are nouns.

Word	Noun	Adjective	Verb	Adverb
interplanetary space	Yes	No	No	No
region	Yes	No	No	No

As nouns, region is a hypernym of interplanetary space; that is, region is a word with a broader meaning than interplanetary space:

Other hypernyms of interplanetary space include part.

interplanetary space (noun)	region (noun)
the part of outer space within the solar system	a part of an animal that has a special function or is supplied by a given artery or nerve
	a knowledge domain that you are interested in or are communicating about
	the extended spatial location of something
	a large indefinite location on the surface of the Earth
	the approximate amount of something (usually used prepositionally as in `in the region of')