Marvel and DC Comics each have their own space-faring police forces. Marvel has the Nova Corps of Xandar, while DC has the Green Lantern Corps based on the planet of Oa. On the surface, these groups of space cops may seem similar, but which of them is stronger? Would one corps be able to outdo the other or would they be evenly matched?
The Nova Corps are based on the planet of Xandar, led by a singular leader designated as Nova Prime. The rest of the Nova Corps are positioned in a tiered ranking hierarchy. At the top is Nova Prime, and after that Nova Centurions, Denarians, Millennians, and standard entry-level Corpsmen. The Nova Corps receive their power from the Nova Force which is maintained by the Xandarian Worldmind, a sentient supercomputer comprised of the knowledge of Xandarians past. A Nova member's level of power from the Nova Force is directly dependent on their rank, with the higher-ranking officers being granted access to more of the Nova Force than those of the lower tier. Nova Prime is the strongest member, having special abilities such as energy absorption, gravimetric pulses, and electromagnetic static bursts. Beyond that, they have the same abilities as the Centurions and Denarians who can fly and have super strength, durability, and energy blasts (with Centurions having more power than Denarians). lower ranking Nova members are more limited, needing ships and weapons to aid in their service. In total, the Nova Corps is comprised of about 500 members.
In comparison, the Green Lantern Corps are based within a central sector of the galaxy on the planet of Oa. The Green Lanterns are led by the group of beings known as the Guardians, who oversee the Central Power Battery of the Green Light of Willpower, which is part of the cosmic emotional spectrum. Each Green Lantern wields a ring to harness that willpower, allowing the user to create green energy constructs, the only limit being their own imagination and the need to recharge once the ring becomes depleted. At one time, the rings were ineffective against anything the color yellow, the color of fear. However, this yellow impurity is now able to be dealt with, so long as a Corpsmen is able to accept their own fears. Like the Nova Corps, the Green Lantern's jurisdiction is the entire universe, which they have split up into 3600 sectors, with a pair of Green Lantern officers protecting and monitoring each one (except for Earth's sector of 2814, which has 6). This means that at the peak of its function, the Green Lantern Corps contains just over 7200 Corpsmen.
It should be noted that both Corps have been destroyed and subsequently rebuilt multiple times over, meaning that neither of them is invincible. Naturally, they both also have more prominent human members than the rest of their fellow officers. For the Nova Corps, they have Richard Rider, who at one point was the only Nova Centurion alive and very powerful as Nova Prime, as well as younger newcomer Sam Alexander, also from Earth. The Green Lantern Corps has Hal Jordan (known by many as the greatest Green Lantern) as well as John Stewart, Guy Gardner, Kyle Rayner, Simon Baz, and Jessica Cruz, all humans from Earth.
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So, which Corps would win the day if they were ever forced to face each other in battle? It seems as though the Green Lantern Corps would win for a few reasons. First off, the Green Lanterns' powers aren't limited by rank, only their own imagination, and personal willpower. Secondly, by sheer numbers alone, they would have the upper hand. While some rookie Green lanterns might have some trouble with the yellow aesthetics in a Nova Corpsmen's armor and energy blasts, it seems unlikely that that would be enough for the Nova Corps to have a full advantage. Although, they might benefit from the fact that their power doesn't need to be recharged like a Lantern's ring. Even so, it appears as though the Green Lanterns Corps would be victorious with all things considered.