using types in my space exploring game

that's what types are for... but you should split all your "things" of the same context into their own types like so:

Const SYSTEM_MAXPLANETS = 9

Type system
	Field name$
	Field size#
	Field planet.planet[SYSTEM_MAXPLANETS]
End Type

Type planet
	Field name$
	Field size#
	Field system.system
End Type

s.system = New system
s\name = "Sol"
s\size = 1

s\planet[0] = New planet
s\planet[0]\name = "Mercury"
s\planet[0]\size = .054
s\planet[0]\system = s

s\planet[1] = New planet
s\planet[1]\name = "Venus"
s\planet[1]\size = .88
s\planet[1]\system = s

p.planet = s\planet[1]

Print p\name+" in the " + p\system\name + " system, is " + p\size + " the size of Earth."
WaitKey
End