Like all planetoids, Nessus is named after a Centaur. In its case, Nessus, was the Centaur who killed Hercules.
More importantly, though the symbolism of Centaurs and the role of the planetoid in Destiny 2 seem very similar. Bungie's attention to Greek mythology shows in its construction of this world, and hints at greater things to come in unravelling the mysteries of our deprecated Solar System.
First, and foremost, Nessus is known as a "visiting" planetoid for a reason: Like a planet, it orbits the sun, but not in a circle. It instead orbits in an acute ellipse which, at certain points, is as close to the sun as Venus, and at others, further away than Neptune, even rivalling the furthest reach of Pluto.
These "Centaur" bodies defy the classic divide of the Solar System: Inner planets, the asteroid belt, Gas Giants and the Kuiper Belt. Additionally, because they don't orbit in the same way as planets or even fellow planetoids, they lack orbital resonance. Should they fly too close to a planet or asteroid, they risk breaking orbit, hurling them into the sun, or else the furthest reaches of interstellar space.
They aren't planets, and they're not asteroids. By sharing the natures of both, they reject the rules of either.
This aligns with the Greek Centaur. As philosophers worked to define what a human is, some worked backwards, asking what a human is not. This lead to fascinating discussions, ideas and even the famous human dichotomy. Of course, this line of thought resulted in an artistic concept that was immortalized by their religion: The Centaur.
In Greek mythology, the concept of humanity was challenged by Centaurs. How can something be both man and horse? Further than how, what's the resulting identity? A similar creature to the Centaur, the Minotaur, has the best example: The legend of Theseus.
In the island of Crete, a yearly sacrifice was made to a Minotaur who devoured seven youths and seven maidens. They would enter a labyrinth beneath the city and be eaten. On the last of such occasions, Theseus entered, aided by the King's daughter, successfully navigated the maze and slew the Minotaur.
The symbolism? That civilization can never truly function without first identifying human nature. The animal nature of man--murder, crime, war--devours us, otherwise. By navigating the maze at the center of the city, Theseus confronts the half-human, half-beast and kills it. Theseus then grasps his humanity fully, reenters the city and becomes a King, himself, worthy as a master of men as he is of his own humanity.
But for humanity, a dying and resurrected species? We're trapped on Earth, without our power, questioning our very existence. We are corpses, but with Light we are living, and with each other, we are Guardians? But without Light, who are we? We are dead things, raised by a power that no longer empowers us.
Enter the planetoid, Nessus, a visiting planet whose nature has been split by the Vex. While converted into a machine world, it remains host to wonderful and magnificent wildlife. But beneath the rock and fauna of its nature, deep, cavernous Vex structures are occupied by older, ancient Vex As Variks notes, "There are gods and powers converging on this system, old machines waking up, old bones whispering flatteries."
Nessus is of two natures: Natural and Vex; Planet and Asteroid.
The question is not "Who are we?" The question is "What is this world?" Its identities are scattered, like the Vex. These machines exist throughout time. If you play the Undying Mind strike or The Vault of Glass, you can be confronted by many iterations of the Vex: Modern Vex, Ancient Vex and Future Vex. All exist in a fragmented state. For the legions led by consolidated minds, singular identity is something they've solved in every physical sense.
But across time? The Vex remain divided amongst each other by their pasts, presents and futures. And for a species that operates beyond time, or at least seeks to, that's an incoherence that must be solved.
In the Vault of Glass, the Vex attempted to write themselves into time itself, consolidating their existences into a solitary one. We crushed this dream, and now they return to Nessus, a world as divided as their existence. And its in this older world, beside their older selves, that they may find their solution--and we may find our answers.
Nessus is going to be a fascinating world, where many ends of lore combine. The Cabal have mining operations on Nessus, the Vex operate beneath its surface, and some hundred years ago, as our Golden Age crumbled, a crew of colonists were sent into the stars by a panicked Warmind, stocked with cargo of human souls and new, powerful, weaponized SIVA. That ship is currently wrecked on the surface of Nessus.
Undoubtedly, we'll find answers. And the Vex may find their solution. But in our present universe where the dead live and the machine operates between past and future, Nessus remains, like the Centaur, quintessentially divided land.