Dinah is an inventive and independent engineer stationed on the International Space Station, informally known as Izzy. Specializing in robotics, she uses machines like Grabbs and Nats to mine metals from asteroids. She is emotionally grounded and resourceful, communicating with her father on Earth via Morse code to maintain a connection to her family.

Dubois, popularly known as Doob, is a prominent astrophysicist and public science communicator. He is the first to calculate the devastating consequences of the moon's destruction, predicting the impending Hard Rain. Tasked with explaining the crisis to the public, he works to balance scientific truth with the need to maintain morale.

Ivy is the capable commander of the International Space Station. She spends much of her time in the station's torus to counteract space sickness. Tasked with commanding a rapidly expanding station and a stressed crew, she faces immense pressure from Earthbound leaders.

Julia is the President of the United States. She is responsible for managing public panic and orchestrating the Cloud Ark initiative. A pragmatic politician, she carefully manages the balance between transparent scientific facts and necessary propaganda.

Aïda is a young civilian selected to join the Cloud Ark through the Casting of Lots. She approaches the challenges of space with an intense, controversial pragmatism. Often viewed with suspicion by others, she advocates for radical, unstructured survival methods.

Kath Two is a Moiran surveyor living five thousand years after the Hard Rain. Tasked with surveying the reseeded New Earth, she is highly adaptable due to her genetic heritage. She is observant and thoughtful, studying the deep cultural divisions present in the Habitat Ring.

Tyuratam is a pragmatic Dinan who works as a bartender and observant Indigen. He carries a scar from the Red-Blue War and assumes responsibility naturally, acting as the eyes and ears for the Owners of the Crow's Nest.

Moira is a dedicated life scientist working on the Cloud Ark. She is tasked with the monumental job of preserving Earth's nonhuman genetic diversity and digital knowledge. Her work involves complex gene synthesis technology requiring meticulous care.

Tekla is a Russian Scout tasked with the dangerous job of rapidly expanding the space station. Accustomed to extreme physical hardship and long hours in a space suit, she possesses incredible resilience and discipline.

Markus is a Swiss engineer who quickly rises to prominence on the expanding space station. He works closely with the command team to test new modules and maintain order as the population swells.

Sean is the driven leader of Arjuna Expeditions, an asteroid mining venture. He is intensely focused on securing ice for propellant, believing it is the key to long-term survival in space, and operates independently of Earth's political structures.

Rufus is a rugged miner based in Alaska. He maintains a close connection with his daughter aboard the International Space Station, sending her messages of encouragement using Morse code over a private frequency.

Cal is a submarine commander stationed on Earth. He is engaged to the station commander, but their relationship is heavily strained by the catastrophic events and their physical separation.

Amelia is a teacher who forms a deep connection with Dubois in the wake of the moon's destruction. She provides him with emotional support as he prepares for his inevitable departure into orbit.

Tavistock is a media anchor who helps shape public perception of the Hard Rain crisis. He focuses on the sensational or entertaining aspects of the catastrophe, serving as a conduit between the scientific community and the general public.

Beled is a Teklan traveler living in the far future. He accompanies Kath Two on her journey from New Earth to the Habitat Ring, possessing the distinct physical discipline characteristic of his lineage.

Ariane is a sharp quarantine investigator from the Julian lineage. She presses travelers for information and holds a complex, potentially adversarial role in the political structure of the Habitat Ring.

Luisa is a new arrival to the space station with a background in psychology and social work. She provides insight into the emotional and social challenges facing the rapidly growing orbital community.

Camila is a Dutch candidate, originally from Afghanistan, who secures a place on the Cloud Ark. She seeks to foster cooperation and avoid conflict within the tense, claustrophobic environment of the station.

Rhys is a tough engineer who struggles significantly with space sickness. Despite his physical discomfort, he contributes valuable insights on using asteroid materials for radiation shielding.

Henry is Dubois's son. He experiences the escalating chaos on Earth alongside his father, trying to find safety as bolide strikes begin to hit the planet's surface.

Pete serves as the science advisor to Julia Bliss Flaherty. He works behind the scenes to manage the political and scientific logistics of the Cloud Ark plan.

Zeke is a crew member with a military background. He becomes involved in the political maneuvering aboard the station as different factions vie for control.

Clarence invokes the idea of Noah's Ark to help the public process the impending disaster, asking communities to select young people for the space initiative.

Einstein is an Ivyn living five thousand years in the future. He claims to have knowledge of pre-Zero artifacts and guides the explorers through the rugged terrain of New Earth.

Sonar is a Cyc who has memorized entire volumes of preserved encyclopedias. She carries the historical and cultural knowledge of an underground society, seeking to establish contact with other survivors.

Rhys is a Dinan individual operating on New Earth. He interacts with Kath Two and Beled Tomov as they prepare to return to the Habitat Ring.