What does the astronaut symbolize in everything everything?

In "Everything, Everything" by Nicola Yoon, the astronaut symbolizes the desire for exploration and the pursuit of freedom. He represents the longing to break free from constraints and experience life fully, contrasting with Maddy's sheltered existence due to her severe illness. The astronaut's journey into the vastness of space serves as a metaphor for Maddy's yearning to venture beyond her confined world and embrace the unknown, highlighting themes of love, risk, and the quest for identity.