Nebulae is a species of monster in Xenoblade Chronicles, and includes Novae which are quest-exclusive variants. They are cloud-like, gaseous enemies made of pure Ether. They can be found on Bionis' Leg, outside Colony 6, in Makna Forest, at Eryth Sea, on Valak Mountain, in Bionis' Interior, and on Prison Island. The strongest Nebula is the Bagrus Nebula, which is at level 96. All Nebulae have a very high resistance to physical attacks which reduces damage by 80%, when fighting them, Ether users are extremely useful.
All Novae and Nebulae can self destruct. When they do so, they inflict a debuff to the whole party and don't drop any treasure chest.
Since Nebulae are basically intelligent floating clouds of Ether, they each are associated with a specific element. The Ether Crystals dropped by each color of Nebula are also named after a planet.
The reason why each types of Nebula is affiliated to a planet of the solar system could be that they were named by Zanza, their creator and a man who came from Earth in the first place.