Augie is a 78-year-old astrophysicist who chooses to remain at the Barbeau Observatory in the Arctic during a sudden military evacuation. Having spent his entire life focused on the stars and actively avoiding personal attachments, he is emotionally guarded and comfortable in isolation. His solitary existence is interrupted when he discovers a young girl left behind, forcing him to adapt to an unexpected caretaking role while contending with his declining health.

Sully is a dedicated astronaut on the first manned mission to Jupiter aboard the Aether. She operates primarily in the communication pod, analyzing Jovian data. Driven by her career, she carries intense guilt over prioritizing her work over her family on Earth. When the planet abruptly ceases all communication, Sully struggles with mounting isolation and her lingering regrets about motherhood.

Iris is a quiet, mysterious young girl who gets left behind during the chaotic evacuation of the Arctic station. She rarely speaks, communicating mostly through a low, wind-like singing and her expressive reactions to the environment. She shadows Augie around the facility, becoming a catalyst for his reflections on companionship, love, and his past mistakes.

Harper is the steady captain of the Aether. He bears the heavy responsibility of maintaining order and morale when the crew loses contact with Mission Control. He tries to keep his subordinates distracted with routines and recreation while quietly harboring deeper romantic feelings for Sully.

Devi is a maintenance specialist aboard the Aether. When communication with Earth ceases, she spirals into a quiet, paralyzing despair, spending much of her time secluded in her bunk. Her deep anxiety about the silence from home occasionally impacts her focus on her critical technical duties.

Tal is a crew member on the Aether who relies heavily on routine and distraction to manage his stress. He turns to video games—the same games he once played to bond with his sons on Earth—to block out his growing anxiety over the communication blackout, sometimes reacting with frustration toward his peers.

Ivanov is an intense and dedicated specialist working in the ship's lab. As the days of silence stretch on, he becomes belligerent and deeply withdrawn, seeking refuge among the photographs of his family plastered across his bunk. He openly expresses anger as a coping mechanism for his profound worry.

Thebes is a steady, emotionally grounded astronaut who provides crucial stability for the rest of the crew. Having suffered the tragic loss of his family in a car accident before the mission, he possesses a calm demeanor in the face of crisis. He copes by staying fiercely rooted in the present moment, offering patient guidance and mechanical expertise to his struggling crewmates.

Jean is a brilliant scientist who eventually transitions away from her career to focus on her family. Her life choices regarding work and motherhood serve as a point of contrast for those around her, influencing how her family members view their own paths and obligations.

Lucy is Sully's young daughter living on Earth. Her memory is a powerful anchor for Sully, representing both deep maternal love and the intense guilt Sully carries over leaving her behind for a multi-year space flight. In Sully's absence, Lucy has grown closer to her stepmother.

Jack is Sully's ex-husband and Lucy's primary caregiver on Earth. He could never fully understand or support Sully's absolute dedication to her space exploration career, leading to their divorce. He has since built a new life, finding a partner who fulfills the traditional family roles Sully left behind.

A lone polar bear roaming the frozen Arctic expanse near the observatory and Lake Hazen. The bear catches Augie's attention during his walks, representing the harsh, instinctual survival of the natural world that Augie begins to closely observe and appreciate.

A wild wolf roaming the frozen grounds near the Barbeau Observatory. It approaches Iris softly and curiously, but becomes the victim of Augie's protective fear when he misinterprets the animal's intentions toward his ward.