Jet Propulsion is the namesake of the show and he is a humanoid alien. He has red hair and can stretch his body, like his parents can. He is excitable, energetic, and extremely goofy. He is tall for his age and he might be older than the other kids. He was instantly popular with the other children the moment he arrived on Earth. He sees the mundane world as a vast and exciting place, and even thinks that words are exciting, such as "surprise", claiming it to be a funny Earth word. He is named after the Jet Propulsion Laboratory. He is shown to be extremely kind, even to people who are mean to him, like Mitchell. He possibly likes Sydney, because he danced with her in How Come the Moon Changes Shape?
He was voiced by Ashleigh Ball, who also voiced Blythe Baxter from "Littlest Pet Shop"