Impressive theory. My only tweak would be adding Earth's Moon, as it appears to be a major part of the Solar System in the past and present. That way, we would have: Mercury, Venus, Earth, Earth's Moon, Mars, Jupiter, Saturn, Neptune, Uranus. So we have 9 planets. That being said, I do believe the Awoken to be the key too - it may well be that The Reef is a gateway to the 9 realms, merely shrouded between the darkness, and the light, which prevents (too our knowledge) the outer solar system from being as affected by the Darkness as the inner solar system was. It could be a case of, if the Awoken were to turn on the city, it would allow the Darkness to flow through the Outer reaches (Note: Though Saturn was the location of our fight with Oryx this could be the start of that process, simply because the Awoken already had a distaste towards the Last City (excluding the Queen of course), it could have already begun). That being said, Xur visits The Reef, which adds to the complexity. Either theory is plausible, but I don't know enough about Norse Mythology to comment further. As there are other references to the Norse in Destiny, I'd say you're one the right track.