Yes, as long as the planet is still there.
The defender defends as normal (playing an encounter card) but with no ships. From the rules on Launch (page 8):
Note that, in a home system, the defense may not
have any ships on the targeted planet, in which case he or she
defends the planet with zero ships.
If green were to draw a green destiny card, they could attack their own empty planet to reestablish a colony (or they could draw another destiny card). Page 7:
When drawing his or her own color, if a player has a home
planet with no ships on it at all (enemy or otherwise), then he
or she may aim the hyperspace gate at that planet to automatically
re-establish a colony there with up to four ships from
other colonies. Doing so counts as a successful encounter.