In the mid-21st century, the world was shaken by the discovery of a mysterious exocomet that was hurtling toward the Sun. Upon closer examination, it was found to be composed entirely of antimatter, a substance so rare and powerful that it had only ever been theorized before. The comet missed the Sun on its first pass but it was captured by its gravity. The calculations showed that it would return from the outer edges of the solar system in 99 years and collide directly with the Sun.
The news of the impending collision sent shockwaves through the entire planet. Some people dismissed it as just another doomsday prophecy, but most recognized the dire implications of the discovery. Panic set in as people began to realize that the end of the world was at hand. Governments and institutions across the globe collapsed under the weight of apocalyptic fears, and the world as it was known came to an end.
But for a select few, the discovery of the exocomet presented an opportunity to save humanity. They began to plan and construct underground cities that could withstand the destructive force of the collision. These cities were built deep beneath the Earth's surface, with reinforced structures and sophisticated life support systems designed to keep the inhabitants alive for decades or even centuries.
As the years passed, the people of the underground cities prepared for the inevitable. They worked tirelessly to perfect their technologies and build their societies. The day of reckoning finally arrived, and the exocomet returned to the solar system. Its collision with the Sun unleashed an incredible burst of matter and energy that was mainly directed perpendicular to the plane of the solar system. The sun was no more. Instead, the intense radiation and stellar winds from the dying star dispersed the surrounding gas and dust, causing a nebula to form, which then expanded and gradually dissipated.
The planets in the solar system were thrown off course by the sudden disappearance of the Sun's gravitational field. The disappearance of the Sun's gravitational well propagated at the speed of light. The closer planets, such as Mercury and Venus, felt the effect first, while the more distant planets, such as Jupiter and Saturn, were only affected after several hours. The trajectories of the planets were also affected by the principles of general relativity, causing them to move following a complex trajectory. In addition, the ejected solar coronary mass made the planets move in an unexpected way.
On Earth, the impact of the exocomet was catastrophic. The surface of the planet was bombarded with intense radiation and heat, destroying most of the flora and fauna that had existed there. The atmosphere underwent a radical transformation, with the composition of the air changing dramatically. Temperatures plummeted, and the condensation of gases caused a thick, impenetrable fog to envelop the planet, which later rained from the sky and formed lakes of liquid air.
In the aftermath of the collision, the underground cities were the only places where life could continue. Most of the settlements gave in to the harsh conditions within weeks or months, but one city managed to survive. Saint Thor, located 2000 meters below the surface in Eastern Europe, had a unique advantage: it relied on nuclear energy as its primary source of power.
The city's economy was centered around the production and distribution of nuclear power. Uranium mines were established in the surrounding areas, stretching far from the city's core and the nuclear fuel was used to power the city's civil infrastructure and industries. The people of Saint Thor also developed advanced underground farming techniques, using artificial light and hydroponics to grow crops in a controlled environment.