Bell is an 11-year-old boy who has spent his entire life inside the United States settlement on Mars. As the youngest member of the colony, he relies heavily on the adults and older teenagers for guidance and companionship. He enthusiastically helps out at the algae farm and spends his free time watching digital reels of Earth. He holds a deep fascination for terrestrial animals, particularly lions, and views his small community as a pride.

Phinneus is the oldest resident of the American settlement and works as the colony's primary farmer and botanist. He tends to the underground algae farm that provides the group with food and necessary supplies. Unlike the base commander, Phinneus holds fond memories of the days when the international settlements collaborated and traded freely. He provides gentle wisdom and stability to the younger generation.

Sairam Dexter, universally called Sai, serves as the Commander of the US Mars Settlement. He operates the base with a strict adherence to protocol and enforces an absolute ban on contacting the French, Russian, Finnish, and Chinese settlements. He takes the physical safety of his ten-person crew very seriously, constantly running emergency drills and requesting advice from Earth Command. His rigid policies stem from past tragedies that occurred on the Martian surface.

Trey is a 14-year-old boy living in the American colony. Desperate to be seen as an adult, he recently requested to move out of the room he shared with Bell to bunk with the older teenagers. He resents performing basic chores and deeply desires to be chosen as Commander Sai's apprentice. His ambition causes friction with his friends, leading him to act dismissive toward those he considers childish.

Albie is a teenager in the American settlement who currently bunks with Bell. He has successfully secured the role of Commander Sai's apprentice, a position that requires him to learn the technical and administrative operations of the base. He goes about his duties diligently, inadvertently causing jealousy among his peers.

Meems functions as the medical doctor for the United States settlement. In the absence of biological parents, she has taken on a maternal role for the children of the colony. She carefully monitors the physical health of the crew while providing emotional support and comfort to the younger generation.

Vera is an older teenager living in the American base. She exhibits a rebellious streak and expresses frustration with the small, confined nature of their colony. She longs for new experiences and frequently instigates rule-breaking behavior to alleviate the boredom of her daily routine.

Flossy is a teenager residing in the US settlement. She handles her assigned chores without complaint and enjoys fashioning nice clothing out of the limited materials available on the base. She possesses strong administrative skills that prove invaluable during unexpected emergencies.

Darby serves as the general contractor and handyman for the Mars settlement. He operates in tandem with his wife to repair and maintain the vital life-support equipment necessary for survival on the red planet. He provides a boisterous, cheerful presence within the small community.

Eliana is the designated engineer for the American colony. She possesses the technical knowledge required to keep the air vents, generators, and solar panels functioning in the harsh Martian environment. She frequently corrects her husband's mistakes when they perform maintenance tasks together.

Salty Bill works as the sole cook for the American base. He spends his days attempting to create varied meals out of the settlement's endless supply of processed algae. He maintains a notoriously grumpy demeanor but cares deeply about providing comfort through his cooking.

Lissa was a member of the American settlement who died in a tragic rover accident several years before the start of the narrative. Her death deeply traumatized Commander Sai and directly caused the total isolation of the United States base from the rest of the Martian colonies.

Commander Sylvie Laurent leads the French settlement on Mars. She runs her base with a focus on joy, community, and hospitality, encouraging social gatherings and parties. She communicates openly with the Chinese, Finnish, and Russian settlements to share resources and maintain high morale.

Amélie is a young girl living in the French settlement. Growing up in a collaborative environment, she casually visits the other international bases and views the diverse population of Mars as one large, extended neighborhood.

Layla is a resident of the French base who interacts with the American teenagers when they cross the settlement borders. She quickly becomes the object of Albie's romantic affections.

Petyr is a Russian settler who resides on Mars. He was present on the surface during the tragic rover accident that claimed Lissa's life, an event that forever altered the political dynamics between the neighboring colonies.

Leo is an old domestic cat living in the American settlement. Unburdened by the political boundaries set by the humans, he frequently wanders the underground tunnels that connect the various international bases.

Muffin of Mars is a mouse that stows away on a supply ship from Earth. The children immediately claim the animal as a pet, ensuring it receives a family surname to signify its official membership in their colony.

Sasha was the Russian woman assigned to safely transport Commander Sai to Mars when he was an infant. As part of the Nanny program, she dropped him off at the American settlement before taking up residence in her own nation's colony.

Rose is the deceased wife of Phinneus Peck. Though she passed away prior to the events of the novel, her memory heavily influences Phinneus and provides the settlement with traditional Earth recipes.