Question

how do you know that planets are made up of gases where there is no atmosphere in space?

Answer 1

by spectrum of elements of that planet.

Answer 2

ya there r no atmosphere in space but..... where there is heavy mass, like in stars, the quarks n leptons in space r fused to form electtons p r otons n neutrons. the 1st element that can be formed is hydrogenn helium n further.... due to its gravitataional pull msny other bo df ies start revolving around the star, when some bodies hit the stars the radioactive elements scattered n slowly this is how all elements r formed dude..... including gases