Lo, I love your imagery!
In my analogy, different gender manifestations would be represented by structural variations in the orbiting bodies: males could be gas planets, females, rocky, the ice giants could represent a third or intermediary gender, and agender could be represented by a body with an undifferentiated structure(?). My thought is that this allows the possibility of a polyphony of as-of-yet uncatalogued genders above and beyond the traditional ones.