Warning! Spoilers for Planet-Size X-Men #1 ahead!
The X-Men have taken over Mars and declared that mutants are effectively the rulers of the solar system. Marvel promised that the month-long Hellfire Gala event would change the future of mutants and the Marvel Universe forever, and they are following through on that promise with Planet-Size X-Men. The massive display of power on the part of the mutants will have enormous ramifications for all of Earth and the surrounding galaxies.
Since the mutants founded their nation of Krakoa, they have steadily climbed up the global political food chain and established themselves as major players on the world stage. They essentially doubled their population following the X of Swords event, where Krakoa’s ancient sister island, Arakko, was returned to Earth from Otherworld and rejoined Krakoa. The millions of mutants inhabiting Arakko have not made a major impact so far, but that is all about to change.
In Planet-Size X-Men #1 by Gerry Duggan Pepe Larraz, Marte Gracia, Clayton Cowles and Tom Muller, readers get a chance to see what the mutants have been planning to unveil at the Hellfire Gala all along: they have terraformed Mars and transplanted the island of Arakko to the Red Planet. They rechristen Mars as Planet Arakko, the first mutant planet, and declare that it is the capital of the Solar System. The planet includes the Lake Hellas Diplomatic Ring, where diplomats from other planets and solar systems can come to settle disputes without war. The declaration also includes a reference to the “Regent of Sol” though who that could be and how far their kingdom stretches is not made clear. In one night, the mutants have completely overturned the power dynamics in the solar system and established themselves as the official galactic representatives for Earth.
It is established in the issue that the planet is ostensibly for the inhabitants of Arakko, as they fought and sacrificed so much in Otherworld to ensure that Earth and the mutants could survive. But Magneto spearheads the terraforming of Mars and its foundation as a mutant planet, so it is safe to assume that the mutants of Krakoa will have major influence on the planet and that they will hold a place of great import during the diplomatic negotiations that take place there. They have set parameters for how others can use the planet by setting up Port Prometheus, the only spot on the X-Men's Mars where galactic diplomats are allowed to land. They have also made it clear that anyone who ventures outside the area of diplomatic immunity provided by Lake Hellas will be at the mercy of the Arakkii mutants.
The unveiling of Planet Arakko makes up the “fireworks” that were expected to close out the Hellfire Gala. The aftermath of this will likely continue to be explored for a long time to come in Marvel comics. The first issue of the Hellfire Gala event, Marauders #21, included a scene taking place after the fireworks where many were shown to be upset and shocked, but it was not known until now what they were reacting to. The final pages of Planet-Size X-Men also includes memos from NASA and the X-Desk of the CIA, showing a degree of panic and disbelief that the mutants have taken this step. By taking over the entirety of mars, the X-Men might have just placed a planet-sized target on their backs.