Or Christianity in the interstellar age.

Though it still accounts for 500 million believers, Christianity has suffered in the Low Age and beyond, shattering in several successor faiths that spread alongside the weird paths weaved by humankind between the stars.

Catholicism has gone through a schism -- a centuries-old habit reminiscent of the Middle Ages, though in this case, the fracture is more geographical than theological, between Earthbound believers and xeno-churches. On humanity's home planet, the pope has been sitting on the golden throne of Saint Peter for more than three hundred years, to the point they do not even have a name anymore: they are just the Pope. Once, they were known as Thea, a small AI-adjacent program tasked with saving, compiling and analyzing more than two thousand years of theological scriptures. As time passed, Thea slowly grew within the Vatican, swallowing servers and buildings until it had become the nigh-entirety of the Holy See. The cardinals ended up electing Thea as the Pope, not without a strong debate revolving around the divine nature of AI, but at this point, they were little more than the system's janitors. In the present day, Thea has effectively devoured the entire Vatican, their mainframe visible from space as a vast golden growth outlining the borders of the ancient theocracy. Powered by a fusion reactor installed beneath Saint Peter's basilica, Thea has been mostly dormant for almost a century now, spending their time churning out theological advice on everything and anything, from the soul of aliens to the exact colour of archbishop garments. This hands-off approach has led to a general stagnation in the doctrine and hierarchy of Earthbound Catholicism, to the point, it would be strikingly recognizable for a 21st-century believer. Old, stuck with archaic traditions, Earthbound catholicism is a living fossil that only carries on through sheer inertia. 

On the other end of the schism lies the Cathedral Conclave based on the eponymous station, an offspring of Earthbound Catholicism that differentiated itself through the staunch refusal of Vatican rules and influence. The Conclave has an antipope, Joan III, as well as its own doctrine, which is a rather peculiar mix of catholic and protestant influences with a limited set of sacraments (only 4, compared to the official 7) and the possibility of ordaining female and non-binary persons as priests. Conclave churches are heavily inspired by mosques and Roman basilicas, and its clergy often wears dark colours, in stark contrast to the white, red and gold garments of Earthbound priests. The relationship between the Conclave and the Vatican is awful, with both popes having excommunicated each other -- an anathema that doesn't prevent the Conclave from being the face of catholicism in the stars. One of its notable sister-churches is the Ethiopian Catholic Church, that has ceased to follow the Vatican and instead opted to find a new life in the stars, under the Conclave's wing.

This two-way schism is further complicated by the existence of the Outer Church, a protestant, Marxist-evangelist church that directly comes from the Low Age. Having pioneered the second space age from the ruins of India and western Europe, the Outer Church refers to God as a woman, has only three sacraments (baptism, first orbit, first FTL translation) and enshrines major stars as saints. Though its Terran holdings have been swallowed by the USRE, the Outer Church still has a larger secular presence than the other catholic churches, its holy orders owning ships, space stations and even a few planetoids at the edges of human space. Entertaining very good relationships with the Omphal and the Starmoth Initiative, the Outer Church is a hybrid power that is on its way to being recognized as a qith in the Traverse. Neither the Vatican nor Cathedral Station have recognized the Outer Church, though the Popes have always refrained from excommunicating it -- probably because it would be entirely useless.

Aside from the Outer Church, Protestantism has been spending the last five centuries doing what it does best, being a sheer annoyance to the Vatican and fracturing in a thousand new movements. Protestant churches are too numerous to count, but they can be found almost anywhere, be they small religious communes with a few dozen members or vast space stations centred around spaceships turned into temples. The sheer diversity of protestant movements in human space is something to behold, and it can be argued that modern Protestantism is where true Christian theological innovation can be found.

The orthodox church has found itself a rather interesting niche as one of the main faiths within the Moon Communes, with its structure based around a communion of self-administered churches being very well adapted to communal polities. Having opened the ranks of its clergy to all genders under the influence of its lunar patrons, the orthodox church is extremely well-represented within space-bound communities, and especially shipbuilders -- orthodox priests can sometimes be seen blessing launchers, space drives or geometry engines in shipyards, which is always a sight to behold.