Resilience is a recently built Mars rover equipped with a chemical laboratory, cameras, and a mechanical arm. Though programmed as a logic-based machine, he begins to develop human emotions by observing the scientists who build and test him. He prepares for his upcoming mission with a mixture of determination and uncertainty, heavily relying on the affection and guidance of his human creators. He views his tasks not just as scientific objectives, but as a way to make his team proud.

Sophie is a 12-year-old girl and the daughter of one of the lead scientists working on the Mars rover project. She writes letters to Resilience to process her feelings about her mother's long work hours and absence from home. Through these letters, she explores her conflicting emotions, eventually finding that writing to the machine helps her feel closer to her mother.

Rania is a lead scientist at NASA focused on preparing Resilience for space flight. She is strict, businesslike, and driven by the immense pressure to ensure the rover operates flawlessly. She struggles to balance her demanding career with her family life, deliberately keeping emotional distance from the robot to protect herself from the fear of his potential failure.

Xander is a scientist working alongside Rania to build and test the Mars rovers. Unlike his more reserved colleague, he is laid-back and treats the machines like friends, playing music for them and offering casual encouragement. He provides Resilience with a vital sense of camaraderie during the stressful testing phases.

Journey is a test rover built by the same scientific team as Resilience. She operates strictly on analytical logic and firmly believes that human emotions are a flaw that will lead to a mission failure on Mars. She frequently corrects Resilience and insists that machines should not experience wants or fears.

Fly is a drone helicopter designed to accompany and assist a rover on the Martian surface. Unlike Journey, he is entirely open to experiencing human-like emotions and quickly adopts Resilience's hopeful outlook. He provides crucial companionship, optimism, and aerial reconnaissance for the team.

Guardian is a satellite positioned in orbit around Mars, tasked with guiding rovers on the planet's surface. She is highly pragmatic and authoritative, viewing herself as superior to the smaller robots working below. She issues strict commands and initially dismisses any behavior she considers unprofessional.

Courage is a preceding Mars rover that went offline during a severe dust storm. Part of the new mission involves locating Courage's resting place and attempting to bring his systems back online to recover data. He represents the physical dangers of the harsh Martian environment to the newer machines.

Sophie's Grandmother provides daily care and support for Sophie while Rania works long hours at the NASA lab. She monitors the family's well-being and frequently voices her worry that Rania is sacrificing too much of her personal life for the rover project.